weird overheating problem


Senior Member
I just replaced two head gaskets on my Chevy and now every time I start it up and let it warm up the temp guage just keeps going up and up. I usually shut it off b4 it gets much over 220. To cure the problem I shut the engine off, open the radiator cap, and then start it up again. The top hose is totally cold before I do this by the way. Anyway, the thermostat seems to open because the temp gauge goes to its normal operating temperature and stays there no matter how much it runs. Any ideas? I have only ran the truck twice before putting the head gaskets on and both times it has done this with the exact same symptoms.


i dont know much about these kind of things but did you check the radiator cap? it has caused me some problems before. i tried to fix everything else and i finally replaced the cap and that did the trick.


Junior Member
Don't know if this applies, but my first attempt at a header gasket, I put it on 'upside down' and actually blocked some of the flow........

75 Addict
I'm a little :confused: here: You have only run the truck twice BEFORE putting the head gaskets on & both times it's done this with the exact same symptoms? Does that mean the problem started before or after the head gasket swap?

I'm wondering if the thermostat is acting up on you - perhaps try replacing it first since it's a relatively simple and inexpensive job.
I'm also confused. Your thermostat is NOT opening if the engine water temperature is 220, but the upper (return) radiator hose is cold! This, in fact, indicates the exact opposite -- with the thermostat sticking in the closed position (which is the normal position it will stick in unless you are using a "no-fail" type of thermostat), all of the coolant will remain in the engine and continue to heat up.

The thermostat should have been changed when you replaced the head gaskets. What temperature of thermostat are you using? Is the engine actually getting this warm, or is the gauge reading incorrectly?

Has most of the air been purged from the cooling system since you replaced the gaskets?

Why did you replace the head gaskets in the first place? It is possible to install them incorrectly, thereby blocking coolant passages. Which engine is this? The 400 small block is especially sensitive to incorrect head gasket usage.

If you can't find your problem, try answering some of the questions everyone has presented to you, and don't worry about providing too many details of the symptoms -- it's impossible to give us too much information!

Hope this helps!


Senior Member
here is some more info

First, no this problem did not happen before I replaced the head gasket.

The engine is a 350

Low compression and water in the oil is why I replaced the head gaskets. The compression is now averaging around 130.

The engine is started. The thermostat is 190 by the way. The temp guage shows overheating past 190 as the engine runs. I shut the truck off. I check the hoses. The bottom hose is warm, the top is cold. I restart the truck and I know the thermostat opens because the temp guage dramatically drops from 220 + to 190 and atays there. The top radiator hose is now warm indicating flow. Maybe there is air in the system since I didn't do anything when I re-installed the heads and intake manifold. I am sure I got the gaskets on correctly as they had references to top and bottom and all holes were lined up.

I am pretty sure the guage reads correctly as it is consistent and normally shows the truck operating around 190(before the h gaskets were replaced).
i know this is going to sound really stupid but make sure that the radiator is full as well as the resevor. after the motor is heated up turn on the heater and check for hot air comming out if there is no hot air then the coolant is not getting to the heat exchange. then you know something is really wrong.


Senior Member

That probably is not the problem bummerkit because the thermostat eventually opens up and the engine does return to normal operating temperature. I don't see it being the cap because it worked perfectly before.

thelawnguy Addict
Central CT
There is air trapped in the cooling system. Let the truck warm up with the radiator cap at the first stop (so any overflow goes into the bottle not the ground). Run it at idle 15 min or so then tighten the cap all the way and you should be good to go.

My Dodge has a bleeder on the t-stat housing (similar to those on a wheel cylinder) to make this job simpler.

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