I posted this in DR as well as I need an answer very very soon..

Guys, I need to post this here as it will affect my drag racing for this week or even the season. As some of you know I've been having an issue with overheating. I thought is was a bad thermo so I replaced it. I still had the problem. I won't bore you with the details, but you guys are my only hope at this point. Here is my 79 vette is doing.

The temp will just keep going up all the way to 280 if I don't pull over and sit for a few minutes. The 160 degree thermo is open at this point, BUT when this happens my heat does not work. It seems that the 5/8 in hose to the intake is hot and the 3/4 to the water pump is not. These two issues seem to go hand and hand. Now over the weekend, after Dennis K came over and we thought we removed any potential air pockets she seemed to run fine and not overheat. In fact, even the next day I went for a small cruise and she work perfectly as did the heat. I have a new water pump so that is not the issue. I also have a thermo with that bypass thingy in case there is air in the system. This first started this past winter. Perhaps, I cracked the block or busted a head gasket. If I did one of these season ending things would the car still perform as it did before the problem? Can a bad block or basd head gasket cause intermitten overheating? Guys please give me some advise or tips here. Ralph, Chris, Eric, Anybody, I only have a couple of days left.......Tony Abbruzze

 

I know .. .back when i had my old 302 ford .. (no comments ) I had a bad head gasket... and I mistaked it for cooling problems for months .. was fine on short trips .. but long one forget about it.. It was letting steam into the water passages and stopping the flow with an air pocket.. no sure if this is your case... but it caused me a tone of head aches... Try a leak down test in all the cylinders.. thats how i found mine

 

I am leaning towards a bad head gasket or cracked block. I guess the air pocket would screw with my heater core as well. Funny thing is no smoke out the exhaust or oil in the water or evan any loss of performance. The other this is that the heads and head gaskets are only a year old. The gaskets seemed like quality gaskets. We torqued everything down and such....Any cheap way to do a quick leak down test?

 

go to a harbor frieght or a local part store ....they sale the tester for somewhat cheap ... and hopefully u already have a compressor.... all it does is pump air into the cylinder and show how much it leaks....if u just find a way to thread the hose from the compressor into the spark plug holes .. you can pump air into each cylinder .. and see if u get bubbles in the radiator... just some ways i can think of... Good luck

 

Would this test be for a bad block as well or just a head gasket?

 

if it is a cracked block, it would have to be a small crack into the water jacket, that would just pump steam into the water for a short time, eventually it would fail more seriously. A Head Gasket could do the same thing and I would think it more likely. If you got allthe air out of the system and it was fine for a day or two, its getting air in there somewhere. You answered the question, one heater hose not getting hot, thats a no flow condition period. So you have a bypass? on the thermostat? What is it?
Try the leak down test, if you think one cyl is failing pull the head and carefully look over the gasket and cyl walls, take pics

 

The thermo came with a tiny little valve like thing that pops up to release any air. Does it work that well- who knows. I should have drilled an 1/8in hole in the thermo.

 

run it without the thermo and see if it still builds air .....if it stops .. replace with one that has a whole drilled... if it still has the problem ... I would leakdown test .....

 

If you had a head issue or block issue your water level would drop. You running water or coolant?More detail is needed on when it is happening. If the car sits and idles does the temp rise? Is it only when you are driving? Is it city or highway. Does it rise to 160 pause and continue??? Does the 79 have an electric fan as well??

Things to check. Do you have a front spoiler...the factory one??? Its not just for looks...it directs the air up to the rad. You will over heat on the highway with out it and yes you will have to stop to bring the temp down.

Just out of storage you say??? Nest between the rad and A/C condensor???

Fan not working???

Bad rad cap???

Bad stat??? I know you replaced it but there are defective stats.

Hope this helps.

Jim