I have an F350 super duty with an overheating problem. I receiveda call from my wife as she was driving the truck saying that it was blowingcold air when the heater was on and the temp was rising. I had her pull off theroad and turn off the truck, pop the hood and see if the coolant tank had anti-freezein it and she said no. I went to meet her with coolant and I filled it back up,and had her run the engine. I didn’t see any leaks from the upper and lowerhoses, radiator, or the water pump. She went on her way and a little over 30mins later she called me about the same issue. I went and bought a newthermostat and coolant. I installed it and it worked for a day and the sameissue came back again (no coolant in the tank and overheating) I figured badthermostat out of the box so I returned it a got another one from a differentstore. The new one did the same thing as well. I noticed as the truck wasgetting hot the upper hose would be soft and the coolant would flow fine andthen the hose started to harden up and I noticed the fill tank started to fillhigher and higher till it was backing out the top fill cap. My thought is theproblem has to be coming from the thermostat area since it may not be openingwhen the temp gets too high. a few mechanics we spoke to about this are hintingtowards a head gasket, now are they saying this to drum up business I meanthere is no added smoke coming out the tailpipe and it is not back firing andthere is no water in the oil or trans fluid. Any ideas would be very helpfulThanks

 

It is possible for cylinder compression to be getting past a head gasket that is not sealing. One of the places that compression pressure can go to is the cooling system.
The leak may be only small enough to leak under high pressure, but can become worse and when the engine cools down pull the coolant into the cylinder area where the pressure is lower when the engine is not running.

 

Hey thanks for your response. Now what about the issue when the upper hose builds up pressure and the fluid ejects out the fill cap??? You didn't respond on that though. that wouldn't have anything to do with the head gasket seal breaking right

 

Mark, when any kind of pressure gets into the cooling system , one of the first places you can notice it is at the upper radiator hose. Generally the radiator cap will hold pressure up to approx 15 lbs. After that the pressure is released into a recovery section of the cooling system reservoir. When addl pressure forces more coolant into that recovery section it has to go someplace and that place is out the overflow.
There are a few tests that can be done to confirm what may be taking place.
One is to pressurize the cooling system with a radiator pressure tester and observe the drop in pressure if that takes place.
Another test is done at the radiator fill opening with a combustion gas detector. If the gas is present then compression is getting into the cooling system.
Another test would apply pressure to each cylinder and see which cyl allows the air to get into the cooling system.
If all the simple and easy tests clear and pass, a head gasket is one of the next things to suspect.
Keep in mind the hot gasses from combustion also add heat to the coolant, and they can and do contribute to an overheating condition.