cooling system woes - with a glimmer of hope!

[fuzzydog]

Sorry this is kind of long but I want to include as much info as possible.
My truck is a 91 F250 7.3 IDI (no turbo, no mods) which I have owned for almost 4 years. It generally does the heavy work in my household and we have a daily driver car.
My expansion tank just started overflowing coolant. Ever since owning the truck I have occasionally smelled coolant but the only evidence of leakage I found was a small purplish coloration where the overflow hose goes into the overflow bottle (I use Turbo Power coolant w/SCA which is purple, but is same formulation as the good old green stuff, and it is diesel rated)

I just came back from a 1000km trip - half the trip pulling my empty 16' flatdeck, and the other half the trailer was loaded with a car. No problems on the trip - the truck just continued to pull like it has from day one.

Today, I warmed up the truck in the driveway about 5-10minutes (it was -5C) and made a couple stops on the way to work (total distance to work is only about 10kms). It occurred to me that the heater was not putting out the heat I would expect but didn't think much more of it.
When I got to work and out of the truck the coolant smell was very strong and was actually dripping out of the engine bay. I popped the hood and the coolant tank was full and overflowing. Great! I came on here and started searching - quickly came to the conclusion that I have blockworm (unlikely as I have always used coolant with additives), blown head gasket or cracked head. But maybe not.
At lunch time I went home and when I got there the coolant tank was once again full and slightly overflowing, and there was definite gurgling in the tank with bubbles coming up. Arggh! not looking good. But, the heater was still not putting out the heat I have come to expect.
After lunch I go back to work and on the way there, all of a sudden my legs are bathed in this hot air blowing out of the heater. Parked the truck pointing downhill and no gurgling, no overflowing. ???
I should note that my factory temp gauge is almost always way over to the left towards the cold end but it does work because when I work it hard the gauge will come up to about the middle, then I hear the roar of the fan kick in and it drops back down. I just figure I have a very effective cooling system.
So, I am wondering if my thermostat is flaky? But would that produce pressure in the overflow tank?
Also, when I popped the hood at lunch time I noticed that my rad cap has 7psi on it. If I am not mistaken it should be a 13psi cap, right? That might solve my whole problem there.
It is very curious that this situation cropped up now, which is pretty much the coldest day so far this year.
oh yeah - the coolant in the expansion tank is clear, light purple and clean. No oil mixed in with the coolant. The oil on the dipstick is black and does not appear to be mixed with coolant.
and no white smoke. At all. Sometimes a puff of black but am told this is 'normal' so I don't worry about it.
any ideas/insights?
I will get a thermostat and rad cap today

 

[towcat]

I run a 7lb. cap on my truck. yes, it does use the overflow tank more often than the 13lb cap does. I haven't had a radiator seam leakage problem either since 1993 in any of my trucks. do get a ford OEM thermostat though, it does make a huge difference in how well your cooling system works.

 

[FORDF250HDXLT]

I run a 7lb. cap on my truck. yes, it does use the overflow tank more often than the 13lb cap does. I haven't had a radiator seam leakage problem either since 1993 in any of my trucks. do get a ford OEM thermostat though, it does make a huge difference in how well your cooling system works.

your not worried about this statement? :

"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.."

http://www.oilburners.net/articles/cavitationartic.html

 

[icanfixall]

A stuck shut thermostat wont cause your coolant recovery tank to overflow. It will cause the motor to run cool or hot... Just depends on if its stuck open or closed. Try draining down the radiator till you can see the top core tube ends. If they have lots of mineral depsots around them the radiator is plugged up. This can and will happen no matter what coolant you choose to run. Using distilled water instead of tap or well water will stop the mineral dropout. Hope this helps and install only the factory thermostat made by ford or international. It opens at 194 degrees. Others will fit but they can't pass enough coolant to keep these motors cool...i

 

[towcat]

your not worried about this statement? :

"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.."

http://www.oilburners.net/articles/cavitationartic.html

so then why when you go the the IH parts counter and ask for a radiator cap for a 1988 S1600/4600 chassis you get a 7lb cap? Both types of castings come from the same mold. See all the trucks in my sig? they all have 7lb caps. I must have been lucky over the years, cooling system problems are the last of my problems. chucking belts V or serp is one thing my trucks are notorious for otoh......
one more thing....I do many things to my IDI's that aren't sanctioned gospel. All I can say is that it works for my fleet. My situation is very different, I have a supply of trucks waiting to be cannibalized to keep the good ones running.

 

[high psi]

When I used to mess around w/VW idi's this would usually signify a head gasket issue with compression getting into the coolant...... Dunno if the Ford idi's do that or not.

 

[fuzzydog]

It is not good. I put on the 13 psi cap today and ran the truck in the driveway for a few minutes - it wasn't even really hot and the coolant was bubbling and gushing out the overflow tank. The upper rad hose and the rad itself were still cool to the touch (it is -1 C here) so it wasn't even heat pressure. Temp gauge was still waaaaaay over to the left.

It HAS to be a blown head gasket with combustion pressure getting into the coolant system. I can't imagine it being anything else.

But it runs so well?!?!? It has been sitting about 48 hours and got down to about -4C in that time. was not plugged in and when I started it up it cranked once, fired and ran smoothly at high idle. No shuddering, choking, sputtering, smoking or anything - just like always. I just can't see it running that well with a blown head gasket! Wouldn't coolant get into the combustion chamber after it cools down and cause problems on start up?
I checked the oil just before starting and it was a uniform oily beautiful black. not even a hint of any coolant in there so I guess that points away from coolant leak in the cylinder walls, doesn't it?
damn - I was putting the sled deck on to go for the first day of sledding tomm. Not happening now

So, I am browsing the forum for info on head gasket replacement but if anyone can point me to a particular thread with details, it would be much appreciated.

 

[FORDF250HDXLT]

your thermostat is stuck closed would be my guess.
replace it with a motorcraft E5TZ-8575-C.

 

[fuzzydog]

your thermostat is stuck closed would be my guess.
replace it with a motorcraft E5TZ-8575-C.

I suspected that initially but as I understand it there is a bypass in the engine itself and besides the truck runs with the thermostat closed during warm up anyway and coolant doesn't come gushing out the overflow?
I was hoping that was what it is but after today's incident (the worst yet) I think I have to accept it is a head gasket.

 

[87crewdually]

It's sounding like headgasket to me.
The pic below is a headgasket that had the same symptoms as you describe until it finally blew out total from between the head and block. Look closely and you'll see the carbon track under the fire ring to the water jacket. The engine never burned any coolant and ran fine, but built alot of pressure in the coolant system.

You must be registered for see images attach

 

[fuzzydog]

thanks for that pic. I'll be digging into this tomm instead of sledding. I'm now just uber paranoid about starting it - worried that it might have coolant sitting in the combustion chamber and will hydro lock. I have to start it to move it to in front of the shop for working on it.

 

[OLDBULL8]

It's a little work. Take the glow plugs out, remove the rad cap, disconnect the fuel solenoid wire on the IP, put the gear in neutral, block the truck so it can't roll. A 1/8" pipe thread will fit in the GP holes, just don't tighten to tight, use compressed air 120 lbs. or as much as you have in each cyl., that will check out the head gaskets and/or cavitation. Best to warm up the engine before doing this. Now if you get air to the rad on any cyl. bring that piston to TDC, air it again, if you get air to the rad it's the gasket, no air, it's prolly cavitation. I've used a 1/8" NPT quick connect where ever you can in the GP holes. It's possible the engine will turn with that much air pressure if the piston is going down.

You can crank the engine with the GP's out, see if coolant comes out of any one.

The engine rotates in a clockwise direction as seen from the front of the truck, and for every 1/4 turn of the engine(crank) each next piston will arrive at TDC. So, When the line on the vibration damper is at the 2 oclock position, cylinders 2 and 5 will be at TDC. When the mark is at the 5 oclock position, cylinders 7 and 6 will be at TDC, 8 oclock has cylinders 3 and 8 at TDC, and back to 11oclock, 1 and 4 will be at TDC.