Overheating, odds it's the thermostat, which to get?

Daryl4

Full Access Member
Joined
Sep 4, 2017
Posts
65
Reaction score
20
Location
Pacific NW
My NA 89 suddenly started overheating, was my daily then the other day on the way to work it cooked itself. Took 4 gallons to fill it back up. This rig has an aluminum radiator that is rather flimsy at the cap and the lips had bent up, so I chocked it up to that for the work day. Then it overheated again on the way home. This time it was holding pressure, cooked out some coolant, but was rather normal overheating I guess. FWIW the overflow bottle was full both times. Both times it got hot climbing.

So I'm hoping the thermostat has just given up as that is the easiest repair and seems likely. I haven't driven it since and right now it's outside idling to see what it does. So far it's warmed up enough to kick cold start, there's no pressure, upper hose is warm, lower hose is cold.

It's outside my apartment and I can't work on it here, I need to drive it about 20 miles to where I can work on it and leave it for a while if needed. If it's the thermostat I think I can handle that. This sucker takes forever to warm up and has a rear heater so it cools ok enough for slow level stuff I think even without much flowing through the rad.

What say you?
 

Daryl4

Full Access Member
Joined
Sep 4, 2017
Posts
65
Reaction score
20
Location
Pacific NW
I got no good read on the fan, I neglected to see how it felt when cold, now warm it's just a bit stiff and moving a reasonable amount of air. But the rad isn't hot, the upper hose is only hot close to the engine, and lower hose is cold. But I can confirm the pump is working, coolant level changes with RPM.
 

david85

Full Access Member
Joined
Feb 21, 2008
Posts
4,820
Reaction score
1,083
Location
Campbell River, B.C.
Ford/Motorcraft thermostat ONLY!!! Do not trust any generic jobber thermostat. Also make sure to check the external bypass next to the thermostat when you pull off the "goose neck" housing.

Hot upper and cold lower hose sounds normal, but idle isn't really putting any strain on the engine either.

How hot did it get?
How fast were you going?
How steep was the climb?

Any foam or bubbles coming out of the expansion tank when it was over flowing?
 

Daryl4

Full Access Member
Joined
Sep 4, 2017
Posts
65
Reaction score
20
Location
Pacific NW
So just went for a drive, about 20 miles, mostly highway all downhill or flat and about 40 deg outside. The temp gauge never even got past C and when I stopped at my destination the lower hose was still cold.

Ford/Motorcraft thermostat ONLY!!! Do not trust any generic jobber thermostat. Also make sure to check the external bypass next to the thermostat when you pull off the "goose neck" housing.

Hot upper and cold lower hose sounds normal, but idle isn't really putting any strain on the engine either.

How hot did it get?
How fast were you going?
How steep was the climb?

Any foam or bubbles coming out of the expansion tank when it was over flowing?

Can I bother ya for a part number on the thermostat, E5TZ8575C? And are there any temp options?

How hot when it overheated, IDK, really hot, pegged gauge.
First time I was on the hwy, 65ish, but it overheated, or at least I noticed it about a mile off the highway. Second time, 40ish climbing a hill. Not too steep, IDK a grade off the top of my head.

No foam, didn't notice much bubble wise, a little bit I think but coolant was boiling so can't say if from boiling or other.
 

david85

Full Access Member
Joined
Feb 21, 2008
Posts
4,820
Reaction score
1,083
Location
Campbell River, B.C.
Yup, that should be the right thermostat. EDIT: I'm not aware of any temperature options for the OEM setting. AFAIK, there is only the stock setting of 190-195 ish.

Even on Rockauto, it seems people prefer the motorcraft (bottom of the list):
http://www.rockauto.com/en/catalog/...diesel,1124299,cooling+system,thermostat,2200

Based on what you're describing, it sounds like your thermostat may be stuck mid-ways. Unless it was a downhill drive the whole way, 20 min on the highway should be enough to at least get up to temperature.

Next time you go for a drive like that, please double check the recovery tank after the engine has shut down and allowed to heat soak for 1-2 minutes. Make sure no bubbles are coming out of the expansion hose. If you do get a small, but steady stream, it usually means a head gasket.
 

Joseph Davis

Full Access Member
Joined
Nov 23, 2017
Posts
170
Reaction score
25
Location
Lompoc, CA
I use a Mac radiator pressure tester and see if the water pressure builds up fast in cooling system because the water will boil in block and push it out, so I set it for 16PSI just a little more than cap pressure and it will take 20mins to reach boiling point. just to confirm bad thermostat. If you have bad head gasket the pressure rises very quickly and will start bleeding coolant out in less than a couple of minutes. Then I would do carbon test to confirm bad head gasket. I hope it is just a bad thermostat. Good Luck
 

Daryl4

Full Access Member
Joined
Sep 4, 2017
Posts
65
Reaction score
20
Location
Pacific NW
Next time you go for a drive like that, please double check the recovery tank after the engine has shut down and allowed to heat soak for 1-2 minutes. Make sure no bubbles are coming out of the expansion hose. If you do get a small, but steady stream, it usually means a head gasket.

I use a Mac radiator pressure tester and see if the water pressure builds up fast in cooling system because the water will boil in block and push it out, so I set it for 16PSI just a little more than cap pressure and it will take 20mins to reach boiling point. just to confirm bad thermostat. If you have bad head gasket the pressure rises very quickly and will start bleeding coolant out in less than a couple of minutes. Then I would do carbon test to confirm bad head gasket. I hope it is just a bad thermostat. Good Luck

When I stopped at my destination only about a mile off the highway and checked things out I could still easily squeeze the radiator hose, it was only ever so slightly more pressurized then cold. I also pulled over half way and checked things out, it was weirding me out that the temp was reading so cold, I was worried the sensor wasn't in the coolant. But nope, all was well it was just cold and still there was no pressure. Made me worry the cap wasn't holding but it has held in the past, looks good and is on tight.

Now on things like blown head gaskets, correct me if I'm wrong but a diesel will act a little different then a spark engine. On spark engines it not unusual to have an engine suddenly overheat under high throttle cause the increase in pressure overcomes the head gasket. But in a diesel the compression pressures are more constant so if somethings blown you'll get symptoms right away. And of course FWIW there's no fluids mixing, no coolant in oil, oil in coolant, etc.
 

Joseph Davis

Full Access Member
Joined
Nov 23, 2017
Posts
170
Reaction score
25
Location
Lompoc, CA
Pressure build right away in Diesel engines because 21/1 compression ratio so if it is leaking into coolant passage, you will know. It can mix coolant with oil just depends where on the gasket it leaked from. The thermostat can work sometime and then stay closed another time, it takes longer for the bad thermostat to boil water at idle, but it will empty a radiator in minutes if the thermostat is bad. When a notice an over heat condition I stop immediately. The only times I have seen a cooked motor, is because the person thought they could make it to the next exit? the reason I use the radiator pressure tester is because I can control when the vehicle leaks water. I tested my IDI to 22psi just to make sure no bad freeze plugs and to check radiator for leaks and replaced thermostat. I also solder my radiator too, because it leaked.
 

david85

Full Access Member
Joined
Feb 21, 2008
Posts
4,820
Reaction score
1,083
Location
Campbell River, B.C.
Now on things like blown head gaskets, correct me if I'm wrong but a diesel will act a little different then a spark engine. On spark engines it not unusual to have an engine suddenly overheat under high throttle cause the increase in pressure overcomes the head gasket. But in a diesel the compression pressures are more constant so if somethings blown you'll get symptoms right away. And of course FWIW there's no fluids mixing, no coolant in oil, oil in coolant, etc.

I've had several engines with head gasket problems over the years and none of them had oil and coolant mixing.

Failure can be gradual or sudden.

Even my 6.9 had issues I didn't know about when I tore it down for a rebuild. It didn't lose coolant or overheat, but one of the fire rings was compromised. This allowed combustion pressures to enter between the mating surfaces of the head and block, eroding both.

My Dad's 6.5 had a more pronounced failure, where coolant would fill up the recovery tank until overflowing. It was not dramatic, but bad enough that the engine could no longer pull coolant back in after it cooled off. After about 100 miles on the highway, you'd have to stop, let it cool and manually pump the coolant back into the rad. Similar erosion of the gasket surfaces was observed here too.

My sister's diesel ranger suffered near catastrophic failure. Overheating started shortly after accelerating on the freeway. Pulled over and saw coolant being lost through the recovery tank. Lots of bubbling, but I managed to limp it home by stopping to let it cool every 5-10 miles. Since this was a failure that matured over the course of less than one hour, no erosion of the surfaces occurred. Even the aluminum head was fine.

My F150's 302 also had failure years back. Drove it with a foaming coolant problem for a few weeks before I was 100% sure it was indeed a head gasket (I was still learning engines back then). No erosion in that case, since the gasser had much lower compression.
 
Last edited:

Daryl4

Full Access Member
Joined
Sep 4, 2017
Posts
65
Reaction score
20
Location
Pacific NW
The first time it overheated I didn't really notice anything till I was sitting at a light about a mile off the highway and it all went haywire. There was a weird knocking, like the engine was kicking, suddenly steam everywhere, the power steering wasn't working, look at the dash and the engine light was on and the temp gauge was pegged. My first thought was that I'd broken a belt and it had taken out a hose, or worse. Get off the road, shut it off and pop the hood, belts and hoses intact, radiator cap lifted a bit but mostly just boiling all the coolant out.

The cap lifted like I said cause the radiator is flimsy the lip that holds the cap down had bent up loosening the pressure holding ability of the cap. I got 4 gallons of water at a near by gas station, tapped down the lips on the radiator and all appeared ok for the rest of the drive to work.

Thinking back the part there that most concerned me was the weird knocking, it felt like a giant was kicking my engine, very weird. It happened a little bit more the second time it overheated. Any idea what that was? If it was a spark engine I'd say it was crossfire, something I've witnessed many times. A cylinder firing too early from the spark jumping wires and suddenly slowing the engine causing it to kick. But I don't see how that's possible on an IDI.
 

david85

Full Access Member
Joined
Feb 21, 2008
Posts
4,820
Reaction score
1,083
Location
Campbell River, B.C.
I'm reluctant to speculate on this part, but I'll try.

If it was a head gasket, then usually it will get worse and worse until the vehicle is no longer usable. If combustion pressure entered the cooling system, blew out the cap, killed compression to one of the cylinders and caused an engine knock...then that should be the end of that. No more running from that point on. At least, certainly not anything resembling healthy running.

Then again, things can expand in strange ways sometimes. In all of this time since the problem first started, did you complete a successful drive where the engine actually reached operating temperature?
 

Daryl4

Full Access Member
Joined
Sep 4, 2017
Posts
65
Reaction score
20
Location
Pacific NW
In all of this time since the problem first started, did you complete a successful drive where the engine actually reached operating temperature?
Uhm, no, only the trip home where it overheated, so I guess for a bit it was at operating temp, and the trip last night where it never warmed up. The thermostat being stuck half open makes perfect sense, not a failure mode I'm familiar with though.

I see no reason to think I have any serous engine damage, it drove great last night, just didn't move the temp gauge much and the heater was only warm.
 

david85

Full Access Member
Joined
Feb 21, 2008
Posts
4,820
Reaction score
1,083
Location
Campbell River, B.C.
Uhm, no, only the trip home where it overheated, so I guess for a bit it was at operating temp, and the trip last night where it never warmed up. The thermostat being stuck half open makes perfect sense, not a failure mode I'm familiar with though.

I see no reason to think I have any serous engine damage, it drove great last night, just didn't move the temp gauge much and the heater was only warm.

I haven't heart of them failing half open either, but it seems to fit the symptoms. Hopefully it will be easy to spot when you pull the thermostat.
 

Joseph Davis

Full Access Member
Joined
Nov 23, 2017
Posts
170
Reaction score
25
Location
Lompoc, CA
Most likely Thermostat, sometime the thermostat will open and other times it wont? And knocking usually happens when the head gasket burns between two cylinder, because when one cylinder ignites fuel it fires the one next to it, stopping the piston for a millisecond causing knock. But in diesel it is rare because IP fires cylinder so usually no fuel in the cylinder next to it until IP fires that cylinder. usually no knocking. I have seen cracked head leaking water overnight and locking the cylinder up because water does not compress very well.
 

metroscout

Registered User
Joined
Mar 30, 2011
Posts
1
Reaction score
0
Location
Las Vegas, NV
There is some info that would be helpful here:
How many miles on the truck?
Is the engine stock (verify size and if turbo charged), stick or auto?
Has it been modified in any way?
How hot was it outside when it over heated?
Have you verified there are no leaks?

...so, back to basics. Have you checked the engine oil to verify level and condition? A blown head gasket can leak one or more of several ways. As to these fundamentals, it does not matter if we are working on a gas or Diesel engine:
When running;
Compression to water.
Compression to atmosphere (you will hear a rapid popping sound).
Compression to oil.
Compression to crankcase.
When engine is off;
Water to crankcase.
Water to cylinder.
Any time;
Water to atmosphere.
Water to crankcase.
Oil back to crankcase (causes low oil pressure).

Basically, the head gasket separates several things from each other. Which ever two have experienced a breach will succumb to that which has the higher pressure. This changes depending on the engine being on or off. For example, oil will leak into water when running but water back into oil when a hot engine is turned off. The most common failure on both gas and diesels is compression leaking into water as these areas of the gasket share the most stress in the form of heat and pressure and they are very close to one another.

Check the fluids before startup and verify levels and condition. If there is coolant in the oil, bad head gasket (it will look like a foamy milkshake). Running it runs the risk of bearing damage. If no milkshake continue on.

Remember that very low oil can cause overheating. The biggest culprits for low oil are 1. A leak. 2. A bad turbo 3. Valve guides and/or seals, and 4. Piston rings, in that order.

A thermostat stuck open will cause the engine to take forever to heat up, longer if moving. Stuck closed and the radiator will be cold (no hot water flowing through it) but the heater will blow hot within a few minutes of startup. If the upper radiator hose is cold then either the thermostat hasn't opened yet or the coolant level is low. If it feels warm it was open briefly or the coolant is low. If the hose is hot the thermostat is open AND the coolant level is full.

Leave the coolant pressure cap off and start it. Let it idle until it reaches operating temperature. Verify gauge operation when cold and hot.

If coolant starts puking out the surge tank for a couple minutes then calms down this could be the thermostats cycling. What happens is the coolant in the engine isn't moving. It gets hot so the thermostats opens. This coolant 'trades places' with the cold coolant in the radiator. That cold coolant hits the thermostat and causes it to slam shut. When this happens the surge tank will burp (therein lies the name. If there is no surge tank then the radiator tank with the cap doubles as a surge tank). Top it off with water only until you get to the bottom of the problem (saves $$).

After a minute or three the thermostat opens again and the coolant level drops a bit. Depending on the ambient temperature this cycling can happen 2 or 3 times. If it stabilizes add enough to get the level to the 'HOT' line. Let it continue to run with the pressure cap off. If it keeps puking again and again and again, there is either a thermostat stuck shut, a dirty radiator, or there is compression entering the coolant system-bad head gasket.

Replace the thermostat with a new one from Ford. DO NOT experiment with any temperature than factory spec. Ford spent tens of thousands of man hours and tons of $$ engineering the right temp. Don't try to 2nd guess them on this.

You may need to drive it to the end of the block a few times to get it hot enough. Just leave the cap off. If it settles down and quits puking but the temp stays up, dirty radiator. If it's aluminum, don't waste time and money on cleaners, flush, or any other gimmicky crap. Buy a new one. If it's old school find a reputable radiator shop. Pull it, take it in and have it rodded out. No flushes, cleaners or crap off the parts store shelf will get the calcium and scale out of any radiator. Servicing the aluminum ones is to be considered a temporary repair and rarely lasts more than a year. If they are dirty I recommend a new one.

You can test it out of the truck. Lean it against the wall and plug the lower outlet with your hand. Use a hose and fill it with water. Remove the hose then your hand and count how long it takes to drain. If it's clean it will be completely empty in 4 seconds. 5 seconds kinda dirty but livable. 6 or more and she's full of crap. The water should rush out hard until it is empty. If it sorta dribbles out the tubes are clogged. It doesn't matter what size radiator out of what size car or light truck when you do this-it's all relative. Number of tubes vs. size of the hose bib...

A radiator will flow however much coolant the water pump forces through it. The dirtier the tubes are the faster the water needs to move. This means the water has less time to dissipate heat causing the engine to get hotter. The more heat the more preasure on well, everything.

If the head gasket turns out bad you need to find out why. Sometimes they just go bad. More often the engine got to hot because of a dirty radiator. The thermostat, head bolts (on torque-to-yield engines), and radiator will need to be replaced as a part of the repair.

Now....I live in the desert. Every car I own gets a radiator replaced or rodded every 100,000 miles. It's cheap insurance. My wife's Tahoe has 225K on it. My F350 440K. My Scout 300K. I've never had to change an head gasket or a tranny in any of them. I do however pick up some nice side $$ putting head gaskets and radiators in. If you do any amount of towing consider adding coolers for trans and engine oil. Those Fords have tons of space between the grill and condenser.

I hope this helps.
 
Top