Cavitation
The Complete Guide

For Oilburners.net
By Eric Williams

    So, chances are, you've all heard of cavitation.  But you've heard so many rumors and clear as mud facts you don't exactly know what to believe.  If you drive a diesel engine, or any high compression engine, you NEED to read this article and understand it, it could save you thousands of dollars.  To create this article, it took years of drudging through stories, facts, experiences, and money.  So without further delay.

    If you don't already know how a reciprocating combustion engine operates I urge you to visit http://auto.howstuffworks.com/engine1.htm and understand that before you try to understand what's going on here.

• The following animation is a cross section of an engine, more specially an older indirect injection diesel engine, notice the pre-cup is where fuel is injected first, instead of fuel being directly injected into the cylinder as in newer diesels, this does not effect cavitation affects.
   

• In a diesel there are no spark plugs, heat from compression ignites the fuel instead of a spark.  Glow plugs are only used for starting a cold engine.  Therefore all diesel engines are high compression engines.
   

• Cavitation is a direct result of an engine having an extreme compression ratio.  Standard diesel engines compression ratios usually range from 16:1 to 22:1. A standard gas engine has a ratio of about 7:1 or 8:1, therefore they do not suffer from cavitation.  Some high performance gas engines range up to about 14:1, and seeing this is a relatively high ratio they do suffer from cavitation like diesels.
   

• Cavitation can be cured with a couple methods, the main cure is prevention.  Use SCAs religiously.  To find more out about cures and preventions check out the Questions/Answers Section at the bottom of this article.

Note: The direction of the arrow in the circle indicates direction of piston travel.

These diagrams are not necessarily to scale and are exaggerated for ease of visualization.
 

1. This frame is during the compression stroke of the engine, the air is cool, hence blue.

2. The piston is moving up compressing the air in the combustion chamber.  The air is warming up.

3. The piston has reached Top-Dead-Center and the air has reached a maximum compression and heat.

4. Diesel fuel is now injected via the injector at a pressure of about 1800PSI.

5. The fuel ignites "KABOOM!".  The area in which the explosion takes place is incredibly small, it is exaggerated in these diagrams.  Because the air is under such great compression, when the fuel ignites the resulting energy release is immense and extremely quick.  The pressure in the cylinder peaks out about now. If you ever wondered why a diesel engine was so loud this is why, the pressure jump is extreme and creates a ton of noise.

6. The pressure is so immense from the explosion of fuel and air that the cylinder walls actually expand.  This is all happening so fast that the piston has hardly had any time to accelerate and move downward. The quick release of energy has to go somewhere and some of it goes into expanding the cylinder walls, the rest goes into pushing the piston downward. Now luckily the expansion of the cylinder walls is not beyond the elastic limit of the iron and it will return to shape just fine after it's expanded. The dotted line is where the cylinder wall expanded from, which is where it is in he previous frame.  So notice when the wall expanded it had to push coolant with it. If the walls were thick enough, they'd be able to withstand the pressure jump and not expand.

7. Now the piston has finally started to move downward from the pressure, and is delivering power to the crankshaft.  The force on the cylinder walls has decreased enough that they have returned to shape.  If you notice though in the previous frame the walls expanded pushing the coolant with them and now once the walls have again contracted the coolant lags behind and a low pressure area is formed, basically a vacuum, which puts tension on the coolant.  The coolant lags behind because it can't keep up with this extreme speed of the wall contraction.  This is all occurring in a few thousandths of a second. The tension formed by the vacuum or low pressure area wants to pull the coolant into itself.

8. So finally the coolant has caught back up to the cylinder wall, but with vicious  speed and force.  Now this is basically what cavitation is, the coolant collapsing in on the vacuum and vacuum bubbles that form.  When the coolant implodes on this vacuum up against the cylinder wall, the cylinder wall experiences extreme mechanical stress and the metal is actually eaten away, slowly but surely.  Even if it's only a nanometer or so, after a couple million hits in the same spot, it'll add up and eventually eat anything away, even a metal wall. Obviously it won't occur as pretty as in these diagrams such as the walls at the microscopic level aren't perfectly smooth so vacuum bubbles will form more in some spots than others, but the basic principle occurring is as drawn. If you don't understand the bubbles that are forming, just don't think about them, just go directly off the diagrams I have drawn.  It is the same principle but less complex.   If you want to understand the bubbles think about this. A good real life example is when you are in the a swimming pool and push you hand through the water as fast as you can, you will see bubbles form, but these aren't air bubbles, they are vacuum bubbles.  When you slow down to a certain speed the bubbles cease to form.  An engine that doesn't cavitate doesn't form these bubbles.

    Unfortunately for me, I understood cavitation too late.  The engine in my truck has been replaced twice due to cavitation.  During the latest rebuild I wasn't sure what I was dealing with, whether it be a leaking head gasket or cavitation.  To make a long story short, I turned the engine on it's side, filled the cooling system with water and pressurized it with an air compressor to simulate operating conditions.  (under normal running conditions the cooling system is under 13PSI of pressure).  And the results are the following.

For finding out what the signs are for knowing if you've been affected by cavitation, keep reading.

Everything has been removed from the engine in these pictures, all this is, is an engine block and two cylinder heads bolted on.  And yes, it's a white engine.

VIDEO of the action.

    As you might guess, when systems in an engine mix when they're not supposed to, the results can be disastrous.  When you are struck by cavitation you get fuel/oil in your coolant, coolant in your oil, a hydro-locked piston, perhaps a bent rod, ruined bearings, ruined injector, and a lot of work needing to be done to fix it all.

To help answer all further questions about cavitation I have created the next section.  I believe this format makes it easier to follow thoughts because of it's organization.

Questions and Answers!:

A: Cavitation is not reversible.  Once it  has begun to eat metal away, it can be stopped though.  To keep the coolant from eating away the metal cylinder wall we must treat our engines with a simple chemical called an SCA (System Cooling Additive) or DCA (Diesel Cooling Additive).  What this chemical does is bond with all the metal walls in the engine.  Cavitation still occurs, but now it will eat this chemical off the wall instead of eating the metal off the wall. 

This article is directed toward older IDI engines manufactured by Navistar International.  Newer engines usually come with cavitation protection from the factory with the use of extended life coolants such as Ford's new Gold Coolant.

Here is some simple advice about how to treat your engine to prevent any harm.  If you have no clue what type of coolant you have or what's going on with your engine coolant, drain and flush your cooling system.  You need to find old style ethylene glycol antifreeze, it's the green stuff.  It also needs to be the low silicate formula, if you don't use low silicate formula, the silicates will mix with your SCAs and create a really nasty sludge in your radiator and it'll destroy your cavitation protection and probably your radiator. 

A perfect example of what is needed is FLEETRITE Antifreeze. FLEETRITE is sold at International parts dealers and probably other places.  You will need 4 gallons of FLEETRITE. (you can find better buys than fleetrite, just make sure it is green LOW SILICATE antifreeze, if it doesn't specifically say low silicate, then it isn't)  Next, go to Ford and buy 2 bottles of VC-8, previously known as FW-16, this is your SCAs.  Sometimes you may also to buy the SCAs you need at the International dealer, it'll be called DCA-4, they don't always have it in stock though.  You can also buy them from Fleetguard/Cummins and it will be called DCA-4 as well.  Then go to the grocery store and buy 4 gallons of distilled water.  It MUST be distilled water, this can't be stressed enough.  With other minerals and metals floating around in the coolant from tap water your SCAs won't function properly and may potentially not bond to walls and you'll be no better off than before. 

Finally fill your cooling system with a 50/50 mix of water and antifreeze and add two bottles of SCAs.  Two bottles is what it requires to reach the amount of concentration to be effective in preventing damage from cavitation.

You will need to get test strips to check your concentration of SCAs from time to time, these are purchased at a Cummins dealer or Fleetguard dealer.  Cummins owns Fleetguard.

Another factor that can't be overlooked is a cooling system that can hold the correct amount of pressure.  Ford's IDI engines need to hold 13 PSI of pressure in the cooling system.  If this isn't so, the cavitation will have a slightly greater effect.  The pressure in the system keep the vapor pressure point of the coolant high so fewer vacuum bubbles will be able to form and then implode against the cylinder wall. Read the Question: "Why is it called Cavitation?"

One more factor is Engine temperature.  If you drive your engine short distances and let it cool off cavitation will have a greater effect.  With no heat in the cooling system it won't build up the 13 PSI of pressure it needs..

A: The ratio of SCAs to coolant is one pint per 4 gallons of coolant.  SCAs come in one pint bottles.  As said before you must use green low silicate coolant in a 50/50 mix with distilled water for the SCAs to work.  As the SCAs are depleted, read "So how exactly do SCAs protect against cavitation?" for why they are depleted, you need to replenish them.  Two pint bottles in 8 gallons won't last forever therefore you need to check with test strips and add SCAs accordingly.

A: Yes, it is possible to overdose your engine on SCAs.  You need to keep your SCAs in a ratio of one pint per 4 gallons.  When you check your SCA levels with test strips, there is a little area on the charts for the colors you want that will tell you where the idea range is.  Too low is bad, too high is bad.  When the levels get too high you can get other problems like sludge in your radiator, decreased cooling ability of the coolant, and it may destroy the water pump.

A: Most any SCAs will work as long as you follow the directions on their labels.  If you buy SCAs from Dodge/Cummins/Fleetguard then it won't be called VC-8, it will be called DCA-4.  VC-8 is what Ford sells.  It is the exact same stuff as VC-8 and they are compatible with each other. 

Not only does Cummins have their own SCAs but so does NAPA.  The only difference here is that NAPA SCAs are not compatible with Ford's or Fleetguard's.

Some SCAs are not compatible because they use different formulations of chemicals to achieve the protection from cavitation.  Ford and Fleetguard are compatible, and Wixkool and Napakool are compatible.

Napa's SCAs are called NAPAKOOL, this is also the same stuff as WIXCOOL.  Napakook, Wixcool, DCA-2 and Pencool are the old SCA formulations.  They are still useful in preventing cavitation but one would assume the newer SCAs are better in someway or else they wouldn't have updated them to DCA-4 and such.  Ford's SCAs have also gone through evolution, they started with FW-14, then FW-15, FW-16, then latest is VC-8. No clue why the change in prefixes from FW to VC though. 

A: SCAs should be checked every 10,000 miles at least.  A good rule of thumb though is to check them every other oil change. 

As they bond to metal walls and are eaten off by cavitation they lose their ability to re-bond to the walls therefore need to be replenished.

To check them you need to buy Fleetguard test strips, the part number is CC2602BDS, you can buy these online or at a Fleetguard/Cummins dealer.  Ford does not make test strips.  On Ford's SCA bottles they say to use Fleetguard test strips.  Basically they are little strips with little pads on them.  These pads have little chemical indicators on them and when you dip the strip into your coolant the pads will change color.  Depending on what color they change they tell you what your levels of SCAs are.  There is a little chart that comes with them to tell you what the different colors mean. 

A: Molybdate and Nitrites are the chemicals in SCAs that bond to the metal walls and provide cavitation protection.  Some SCAs from different companies may use other chemicals or one or the other.  Therefore once you start using a certain SCA brand you should keep using it instead of mixing various types.  The most recommended is Ford's VC-8 and/or Fleetguard's DCA-4 because they provide the same protection and are able to mix if need be.

A: SCAs are chemicals that bond to metal.  When they bond to the metal of the cylinder wall they build up a small barrier between the metal and the coolant.  The coolant still cavitates, but now when it cavitates it eats away this chemical barrier instead of the metal wall.  The chemicals that form the barrier bond with all the metal in the engine so that there decreases their levels somewhat.  Also, they can only bond to the metal walls once.  Once they are eaten off by cavitation they cannot re-bond back and therefore their levels are constantly slowly decreasing.  You need to check your system levels at least every other oil change with test strips and add SCAs accordingly.

A: You'll know something is awry when look inside your radiator and see a black film of oil floating on top of your coolant.

There are several other signs to hint you in on maybe you've run out of luck.

They include:
Fuel/oil in your coolant (could also result from oil cooler problem)
Coolant in your oil (could also result from oil cooler problem)
Hydrolocking engine ( coolant fills up the cylinder instead of air, and as you may know coolant isn't very compressible, so when you go to start the engine, it can't turn over)
White or sweet smelling exhaust clouds
Coolant dripping out your tail pipe
Starter breaking off engine (this is caused from the hydrolocking, nothing is moving and the starter is pushing, something is gonna break)
Bent Rod (another possible result of hydrolocking)

A: Don't get too worked up.  If you haven't had any problems with cavitation then you're in the clear, but you need to get your engine treated as soon as possible.  Cavitation damage cannot be reversed but it can be stopped.  Treat your engine as outlined above in the first question and you'll be just fine. 

If you have a newer engine chances are you're fine.  Cavitation is well known to manufactures nowadays and they have pretreated coolant they use with SCAs already in it.  For Example, newer Powerstrokes come with pretreated coolant. If your engine is older than a 96 or so, they didn't come from the factory with protection and you need to do something.

A: There are two IDI's that are used in Ford Trucks.  The 6.9L IDI and the 7.3L IDI.  The engines are identical in almost every aspect except one, the thickness of their cylinder walls, and it just so happens 6.9Ls have the thicker walls and suffer from cavitation far less often.  Back in 80's and 90's when diesel engines became more available in more consumer trucks, people began to use them more.  Basically the public became the genie pig for Ford and other companies when it came to diesel engines.  To get a little more power and a little better emissions out of their 6.9L engine, International, the people who build diesel engines for Ford, decided to bore out the 6.9L to a 7.3L.  Everything seemed great until people started getting 100-200 thousand miles on their engines and started getting odd leaks in the combustion chambers through the cylinder walls.  The problem was ignored for a little while but eventually Ford caught on that they should do something and began telling everyone about SCAs. 

So, essentially the design of a diesel engine can effect how cavitation effects it.  The main factor seems to be the thickness of the cylinder walls.  The thicker they are, the less the cylinder walls can flex and spring back due to the pressure spike during the ignition of fuel and therefore they don't push and pull coolant into themselves, hence no cavitation.

It's like the example of your hand through water up at the last diagram caption.  If you move your hand slow enough through the pool water no cavitation bubbles form. A non cavitating engine's cylinder walls don't spring back and forth fast enough to develop these vacuum bubbles in the coolant.

Another factor that some seem to believe causes cavitation in the 7.3L IDI is the placement of the CDR (Crankcase depression regulator).  The CDR allows any blow by past the cylinders to be put back into the intake of the engine and be burned avoiding any buildup of dangerous gases in the crankcase.  The placement of the CDR directs most, if not all, of the blow by to the rear two cylinders, number 7 and 8.  This blow by has oil and combustible gases in it and makes the combustion temperatures higher than normal in these two cylinders.  It just so happens that number 7 and 8 cylinders are the most common ones to cavitate too. Overall if there is more heat in the cooling system which would result in higher pressure cavitation will be reduced, but if there is only a higher localized heat, that area may be more susceptible to damage.

Another explanation for number 7 and 8 cylinders cavitating more is that they are around a bend in the cooling system in the block.  The coolant has to speed up as it flows around the cylinders therefore giving it less pressure and therefore allowing it to be pushed away from the cylinder wall more easily and allowing vacuum bubbles to be more easily formed..

So more heat and less pressure is a very bad combination for our engines, it's a very good one if you are cavitation and wanting to kill an engine.

Also, for some unknown reason cylinder 4 is a likely candidate for cavitation, perhaps some of the previous explanations occurs here as well, such as thinner walls than the rest and some sort of coolant flow.

The real life pictures up above are of cylinder number 4.

A: A RDT is a Road Draft Tube.  This takes the place of a CDR, crankcase depression regulator.  As said above the CDR directs blow by into the intake of the engine, but sometimes it directs it in such a way that most of the gases from the CDR are directed to the rear two cylinders causing excess heat to build up in those two.  What a RDT does is vent those crankcase blow by gases into the air instead of into the engine.  This may help with cavitation but if you treat with SCAs you should as usual be good to go.  If you have extreme blow by anyways you may be looking at more problems with your engine than having to worry about cavitation.  Your rings may be on their way out and you may require an overhaul.  But I won't really get into that here.  If you have questions about this please direct them to the forum at www.oilburners.net.

A: If your engine has progressed to the point it looks like the engine in the picture up above then you are going to have to do some serious work.  First off, you need to consider your options.  One option is to remove your engine and get it re-sleeved, if you do the work, that option is about 2000 dollars in total for all the gaskets you'll need and all the work you'll need done at the machine shop to get it re=sleeved.  The next option is to buy a short or long block and just put it in your truck and go, that option will cost about 2000 dollars for a short block, and maybe 3-4,000 dollars for a long block, but then at least you have a new engine hopefully rebuilt by professionals and maybe a good warranty.

Either way you'll be working on your truck for a few days.  Pulling the engine is a chore, and if you have a Econoline Van, then give yourself at least a month or two to do the work. 

When you get your engine re-sleeved it's like the opposite of having it bored out.  They actually take metal sleeves and pretty much jam them in the engine replacing the cylinder walls.  If you ever get your engine re-sleeved make sure to get every single cylinder sleeved.  If cavitation has eaten through one cylinder it can't be far behind eating through for the rest.

Even when buying a short or long block ensure that all cylinders have been sleeved.  Some remanufactures only sleeve if there is a leak.  So it may be possible that you install your new engine and 10 miles down the road have a pinhole from cavitation.  So please, save yourself and make sure they sleeve all cylinders.

A: I really have no evidence of this and to tell you the truth I really don't see how it's possible.  Some people have claimed it cured their cavitation pinhole but I'm not too sure about that.  I suppose if you know your engine is cavitated through and you can't work on it, and need your truck, you have nothing to lose by putting in some Bar Stop leak, if it fixes it, good, if it doesn't, you're back to where you were.  In all honesty, even if it does work, it can't work for long.  Only use this as a last resort if you can't afford a new engine or can't afford the time.

A: One thing big engine manufactures do is they make their engine use wetsleeves.  What this means is that when cavitation eats a hole in the cylinder wall, the wall can just be pulled out and a new one put in without heavy machining work needing to be done.  Obviously the engine has to be all taken apart but it's alot easier to do than resleeving a normal engine.

There is also a new type of coolant that can be used.  It's called Evans coolant.  This is a totally different type of coolant and it has different properties from water.  Water's molecular cohesion is what causes cavitation to happen, Evans coolant does not have this type of molecular cohesion. When the cylinder wall pushes out and pulls back the Evans coolant can keep up, no vacuum forms.  The only draw back to this option is Evans coolant is extremely expensive, and your cooling system must be totally absent of water.  It also requires a new radiator top to run at zero pressure.  If you use normal green coolant with SCAs there is no real reason to switch to Evans unless you have some sort of specific reason.

Here is a quote from a user of Oilburners.net about some advantages to running Evan's coolant.

"In case you were wondering if Evans coolant has any other benefits, the biggest is having a 375 deg non pressurized boiling point. It's darn near impossible to damage an engine from overheat or blowing a hose/heater core/radiator etc. unless you never bother to look at the temp gauge because it's going to be pegged to the right for a long , long time before damage can occur.
I put that stuff in all my cars after blowing a head gasket from a quick overheat from a stuck thermostat on one of my Volvo diesels.
6 months later I had a serious temp rise from a stuck air box flap thermostat on one of my gas burner cars while pulling a heavy trailer in west Texas, Pegged the gauge, didn't loose a drop of coolant( non pressurized, big hole in the cap and no damage to the engine, aside from a bunch of melted sensors and wire clips from the high under hood temp. Try that with the green stuff.
Definitely worth the extra money, cheap insurance. My truck will be getting it when I get a new radiator in for it."
-Robert (user: RLDSL)

A: There is a little debate over what ELCs can do to an engine.  If you run a newer engine such as a Powerstroke, ELCs that have chemicals in them to protect against cavitation are perfectly fine.  However, if you run an older engine such as an IDI there may be problems.  The older rubbers and materials in the cooling system of the IDI may be susceptible to failure when in the presence of ELCs.  It is a take at your own risk kind of thing.  From what is gathered though, they do protect against cavitation, as long as it says on the labeling, but just because you don't get any damage from cavitation doesn't mean you won't have problems in other areas of your cooling system.  There are many that run ELCs in IDIs and claim to have no problems.  The advantage is you need to change your coolant far less often.  But for me, why risk it?  I'll just change my coolant every 30,000 miles or so and be happy with my engine.

A: I can't speak for all engines types, but if you drive a 7.3L IDI and run untreated it's almost exactly at 150,000 miles is when you'll get a pinhole in your cylinder wall.  It has happened to me twice and both times right at about 150,000 miles on the motor. 

A: For alot of heavy use engines, manufactures put on coolant filters to keep the coolant clean.  An added advantage to this is you can get filters that have solid bits of SCAs already in them.  As they filter your coolant they also release SCAs, therefore your SCAs will always be in check until the SCAs run out in the filter.  When you use these you still want to check your SCA concentrations as usual, every 5 - 10,000 miles at least.  If nothing else at least your coolant is being filtered.  Most that run these discover after they change the filter out, the old filter has sand and all sorts of gunk in it.  Less gunk and sand keeps your water pump happy!

The filters with SCAs in them come in different sizes and different amounts of SCAs inside them.  For a typical 8 gallon cooling system such as on Ford IDI you usually want a 4 unit pre-charged filter.  You may be able to get away with an 8 unit but a 4 unit should keep your levels pretty good for a while. When you use a filter that is pre-charged you will need still put in SCAs from a bottle to get the levels up.  Once the levels are up, the filter will help keep them there.

You can install your own filter pretty easily.  You'll basically just have to install it in series with your heater core, usually people mount the filter down on the frame rails or under the hood where they can find space and run all the coolant lines to it.  Usually, if you go to an International dealer and tell them you want a coolant filter head they'll know what you're looking for, then tell them you want a 4 unit pre-charged coolant filter.

If you get the filter head from Napa the part number is 4019.

Here are some sample pictures of what a coolant filter install looks like.  These are from pafixitman.

A: No, there is no way to tell how close an engine is to cavitating through.  There is no test that can be performed, at least non that I am presently aware of.  If you are buying a used truck and don't know it's history, the only thing you can do is buy some Fleetguard test strips and test the coolant. If it has SCAs in it you know the previous owner was aware of cavitation and treated appropriately, if there are no traces of SCAs then you must be weary.  If there are less than 150,000 original miles on the engine though, you should be able to treat it and be okay.  As said, cavitation damage can be stopped, just not reversed.

A: From what I have heard the first people to realize cavitation was happening inside an engine was CAT.  Supposedly in the 80's they started a study about cavitation.  They were the ones who came up with SCAs and ways to protect high compression engines from damage.  They discovered more heat and pressure in the cooling system actually slowed cavitation.  On their engines that were run with smaller loads failed sooner than the more heavily worked engines.  Also, if the engines were allowed to cool down more often they failed more quickly.  Ford apparently didn't know about cavitation until the late 90's.  My truck is a 92 and not in one place in the owners manual does it mention cavitation or any special coolant to use.  A few years after having to replace the engine due to cavitation they sent us a letter in the mail alerting us to put SCAs in our coolant to avoid damage.  Infact, I still have this letter and it is dated January 1998.

A: In theory, yes you are.  More pressure in the combustion chamber will make the walls flex more than they do normally.  This area hasn't really been studied but as long as you run SCAs properly you should be fine.

A: Well there are many methods to do this, there is no one set in stone way.  If you can think it through in your head you can probably come up with a way yourself, but some have done research and I'll provide you with that here, again, if there are any questions contact www.oilburners.net with your questions.

From Joe "pafixitman"
"Most likely the easiest test is a a combination of two. The first being a coolant system pressure test. This is very simple as instead of applying pressure to each cylinder, it is applied to the entire cooling system. This test is usually done to about 25-30 psi and will show a leakdown of any coolant joint, or a through hole in a cylinder. Test kits are available from any auto parts store. One thing to keep in mind though, a leakdown will not necessarily mean a back block, it may be a bad pump, hose joint, etc. The second test is to measure the pH of the coolant. As exhaust gases are passed into the coolant, it will become acidic. This will also indicate early head gasket failure (although in diesels, there is a permissible blowby which is acceptable due to the high compression ratio).


Another check is at initial start up. Usually this is done in conjunction with test #1 (pressurize the cooling system). As on cold start up, with a pressurized cooling system, cylinder leakage should show up as vapor or excessive water from the tailpipe, this is due to no catalyst function on a cold start. Also check the oil for signs of any water/coolant present. As on shutdown, a cylinder hole will continue to flow into the cylinder, past the rings, and into the crankcase.
To accurately pinpoint the cylinder leaking the full steps are as follows:
1. Warm up the engine
2. Remove all glow plugs
3. Remove valve covers, rocker arms, and pushrods
4. Using an adapter that threads into the glow plug hole, attach compressed air (100-175psi)
5. Wait 3 mins for each cyl being tested.
6. A failed cylinder will make the Coolant level slowly rise and then overflow from top of radiator. It won't blow out of the radiator, but it will be obvious.
NOTES:
o Valve train should be removed to allow the piston, in the cylinder to be tested, to drop to BDC when shop air pressure is applied. This insures the valves will be closed and the entire cylinder surface can be tested under pressure.
o You can purchase an air pressure adapter at most tool shops (they normally are sold to adapt a compression tester to the glow plug hole)
o The cylinders that are most prone to cavitation are listed in order. #8, #7, and #4. Be sure to test all cylinders as I have seen some of the other cylinders occasionally deviate from this norm.
o Most coolant leaks into the cylinder will show as the glow plug tip will be wet on the bad cylinder."

Also from "obinella"
"Fill cooling system full of liquid to point of overflow, leave cap off. Piston down-valves closed, pressurize cylinder. Observe coolant at radiator. Neck for a period of time. (patience) If it gradually overflows, bleed pressure and move piston to TDC (top dead center). Valves closed, restrain the crank to prevent rotation, re-pressurize. Does the coolant still gradually overflow?
Results,
1. overflow piston down = cavitation or head cracked or head gasket leak
2.overflow piston up= head crack or bad head gasket
3.no over flow but coolant in crankcase=cooler problem"

A: The erosion process is called cavitation after the term cavitation as when a boat propeller cavitates through water. It is the same principle.  Cavitation basically implies the formation and collapse of cavities within the fluid we are studying.  The dictionary states "The sudden formation and collapse of low-pressure bubbles in liquids by means of mechanical forces, such as those resulting from rotation of a marine propeller."

The difference here is ours is resulting from mechanical forces of a cylinder wall expanding and contracting, not a marine propeller spinning.

Here is a good excerpt from http://www.mcnallyinstitute.com/09-html/9-10.html

"Cavitation implies cavities or holes in the fluid we are pumping. These holes can also be described as bubbles, so cavitation is really about the formation of bubbles and their collapse. Bubbles form when ever liquid boils. Be careful not to associate boiling with hot to the touch. Liquid oxygen will boil and no one would ever call that hot.

Fluids boil when the temperature of the fluid gets too hot or the pressure on the fluid gets too low. At an ambient sea level pressure of 14.7 psia (one bar) water will boil at 212�F. (100�C) If you lower the pressure on the water it will boil at a much lower temperature and conversely if you raise the pressure the water will not boil until it gets to a higher temperature. There are charts available to give you the exact vapor pressure for any temperature of water. If you fall below this vapor pressure the water will boil. As an example:

A: There is probably no way to know for sure if electrolysis has any factor in all of this.  From what is observed the answer is no, but we may never be 100% sure about it. Even if electrolysis does have any effect in all this use of SCAs does stop damage. 

If your engine is grounded to the frame properly there shouldn't be any problem anyways with electrolysis. 

    Hopefully you now know what cavitation is and why we need to protect against it's effects.  Our best defense to any problem is knowledge and now you hopefully have knowledge.  It has taken me probably 5 years to collect all this knowledge together.  Countless hours of talking to people more educated than I about the subject, countless hours of them talking to me about their experiences and observations, and then countless hours of me and my personal experiences.  I plan on keeping my truck for a very long time and the less work I HAVE to do on it the better.  It's not that I won't keep working on my truck, but I want it to be because I want to work on it, not because I have to.

Helping yourself is a simple thing to do, in most cases just get a couple bottles of SCAs from Ford and Fleetguard and pour it in your radiator.  A small 10 dollar bottle can save thousands of dollars.   

Finally I'll leave you with this thought.  After many years of working on a van in which spaces are so tight I can't see what I'm working on, only my hands can fit, I have to learn to see with my hands.  With enough experience I can do anything without even seeing it.  When it comes to cavitation the spaces are so small and so closed in, my hands can't even reach.  Therefore I must use my mind to see what is happening through observations and studies.  So, as someone far wiser than I once said, "You don't need eyes to see, You need vision." 

If there are any questions regarding anything in this article please visit www.oilburners.net, register, and ask away.  Everyone is willing to help out.

Glossary :

Cavitation: The formation of bubbles, vacuum bubbles really, in fluid under tension which occurs in the cooling system of a high compression engine which results in failures between barriers of the cooling system and combustion system in the engine, such as the cylinder walls, when these vacuum bubbles collapse.  The implosion of these bubbles against the cylinder wall exert a lot of mechanical stress on them, pinholes form then allow coolant to enter the combustion chamber and wreak havoc.

SCA: System Cooling Additive

DCA: Diesel Cooling Additive (aka. System Cooling Additive)

Diesel Engine: Engine developed by Rudolph Diesel, compression ignition not spark ignition.

FLEETRITE: Standard low silicate Ethylene Glycol Coolant available through International dealers.

Molybdate: A chemical used in SCAs to prevent cavitation erosion.

Nitrites: Chemicals used in SCAs to prevent cavitation erosion.

Glow Plug: A metal plug that heats upon current flow.  Used in aiding start ups for diesel engines.

ELC: Extended Life Coolant

IDI: Indirect Injection