Overheat After Head Gasket Change

razorcat · April 3, 2011

Hello,

I have a 89 GMC 5.7L with 68,000 miles. My Dad bought it new and just didn't drive a lot. It recently blew a head gasket and I did a swap of both gaskets and had a valve job done. Now got an issue. When first starting and driving, the temp gauge will go right up to the red before the thermostat opens and lets it cool off. Once that happens, the temp stays around 190-200 if idling, or around 210 on interstate. It will stay at those temps with no problems until it is shut down and cools off, then it's back to hitting the red mark again before the thermostat opens up. I put in a new thermostat when doing the heads, and have replaced that one again to see if the new one was bad. I'm wondering if the head gaskets could be on backwards. The gaskets had no markings on them at all saying which side was up/down or right/left. I repeatedly looked for any markings on the gaskets and found nothing. I used the Felpro set. Is it possible to put these on wrong side up, and does that sound like the problem? I really didn't want to pull those heads again... Thanks for any advice.

alvocado · April 3, 2011

Are you sure you don't have air in your coolant system? It sounds like a coolant flow issue provided your thermostat is operating correctly.

rogerf · April 3, 2011

Are you sure you don't have air in your coolant system? It sounds like a coolant flow issue provided your thermostat is operating correctly.

Thinking along the same lines...but what caused the head gasket blow in the first place? Running hot on the expressway points toward a corroded rad core or other coolant circulation issue.

razorcat · April 3, 2011

Yes, I've also been thinking there's a coolant blockage issue. That's why I was wondering if my head gaskets could be on the wrong way, and I blocked a water port. Or, since those gaskets were not marked, do they have a "correct" side up? Will either side up work?

It only runs hot the first time its started after it has cooled down, irregardless of being on the interstate or in town. The temp gauge will climb right up to the red, hold there a few seconds, and then it appears that the thermostat opens and the gauge drops real fast back to the center. It will stay there until it is shut off, cooled down, and restarted. I tried to purge air from the system by cracking open the temp sending unit to let air seep out. I only have anti freeze coming out around the threads now when I do that. Any other tricks for purging air?

Something else....when idling with the rad cap off and it warm, I never see a real ciruclation of the radiator. The level will raise and drop a bit, but it never really circulates. AGain, I was wondering if I had put that head gasket upside down and blocked a water port which would cause it to not circulate good. Or, could my radiator had gotten clogged up at the same time the head gasket blew?

Thanks for the help.

Doug_Scott · April 3, 2011

Have you tried starting the engine, and letting it idle until the gauge starts to show it is overheating (or real hot) and feeling the rad hoses? Were they real hot or just warm? Are the heater hoses both real hot?

If the head gaskets were upside down, they would still be upside down after it got hot, so I doubt that is the case. I would imagine that if you noticed they did not have markings to say which side was which, you would have placed the gasket on and looked at the openings to see that they lined up.

Could you possibly have the thermostat in upside down? I know you should not be able to do that, but, stranger things have been done before. Is it possible you have the wrong thermostat in there? I know you have changed it already, but, if you got it from the same place/guy both times it is possible you got the same wrong one both times.

Generally if the temp goes to a very high temp, then drops, it means a stuck thermostat. If the temp is normal at slow speeds, but gets hot on the highway, that generally means a plugged rad or the fins are rotted off the rad. If you have an air lock, it will normally overheat once, and that forces the air out. After that, it would be normal again, even on a cold start.

GPSilverado · April 3, 2011

Could you possibly have the thermostat in upside down? I know you should not be able to do that, but, stranger things have been done before.

This would be my first guess as well. The side with the spring goes down into the intake. Having it backwards would take forever to open it, but once open, the hot water flowing over the spring would allow it to remain open, probably working almost normally until the coolant cools off when sitting.

razorcat · April 3, 2011

I was considering just removing the thermostat to take it out of the equation and see what happens. I'm 99.999% sure I did not put the thermostat in upside down. When I pulled the other new thermostat out, it was in the correct way. Replacing the thermostat did not change any of the symptoms. I bought the two thermostats at different stores: first at Advance, second at Napa.

There's got to be a coolant blockage somewhere. I was just concerned that I had the gaskets backwards and that is causing the blockage. Maybe my radiator is clogged up? I guess the only way to check that is to take it to a radiator shop? If the radiator was clogged up and was causing some higher than normal operating temps, would that cause the head gasket to fail?

Thanks again.