Bought my second Corvette about two months ago. It's a '79. It has the Edelbrock performer intake and aluminum heads and mild crane cam. I changed out the Q-jet for a Holley 650 and the car runs great, lot's of power. My question or problem is that around town or at idle the car's temp stays on the first hash mark on the factory gauge. When I get up to highway speeds the temp gradually climbs up to the 220 mark on the gauge. That's where it stays as long as your up to speed. When you slow down the temp drops back down to the first hash mark. I got the car up to 220 on the gauge then pulled over and shot the top of the thermostat housing with a laser device and the warmest spot was 212. Shot the radiator and it was around 140 at the bottom and 190 at the top hose. The intake read around 160. Water pump was 210. Here is my question. Do these seem to be normal temps? The outside temp on that day was 98 degrees. Is 212 too hot? Is it strange that the car would run hotter at highway speeds than at idle?? Is this too hot for aluminum heads???

I read almost every post on overheating on this site. One was recent and simular to my problem. My spoiler is intact, the rubber seals along the radiator are there. According to the receipts I got with the car the radiator was changed out 6 years ago. So far I have changed the thermostat (160 degrees), changed the fan clutch, and installed a new sending unit. None of this made much difference. I read about the timing issues. I do have a timing light that I bought in 1972 that I will try to find, but I read the total timing post about trying to get 36 degrees total and I don't really understand that concept. Anyway, do I have a problem or am I just paranoid?

Thanks,

Capt. Ron

 

Seems Normal as my 81 does the same thing . This was in Arizona in the summer time but I have since moved to WV and it does run a bit cooler here .
Maybe my 81 is Abnormal............

 

Nope, your ok, that is normal behaviour. I think the deal is that the head gaskets may not have the passage holes just right to cool the heads fast enough. Thats just a guess since I have done NO research on this. I had a book I can't find that had the water flow diagrams in it for SBC. Will keep looking

 

On the timing issue. If your not acheiving the proper total advance at highway speed, your timing is actually retarded. This could cause it to overheat because the combustion is occuring later (when the piston is on its way back down) than required and the walls of the cylinder are exposed to the burn longer than normal.
This may not be your exact problem, but I hope it helps you to understand the process.
Good luck

 

Since your car has a non original radiator, the cooling capacity of the radiator might not be equal to the original design. Different number of fins per inch and things like that. That happened to me. I ended up putting a 4 core unit in. Works fine.

 

Mine also runs warmer on the interstate, just like yours it creeps up towards 220, but settles right back down on secondary roads. To me, as long as it stays on the lower side of 220, I'm OK with that, if it goes over, then I'll start to get worried.

 

It is probobly O.K. but I like mine cooler. The 160 thermostat is not helping you, you really don't want it to go below 180. I test mine in a pot of water with a meat thermometer. I like my temp at 200, I figure that gives me a factor of safty. There are several ways to help this, I'm going to try installing an oil cooler (mine is operating at 210). Then there are new aluminum raditors, ect. Dewitt's are the experts in this area, $$$ but fair.

 

220ºF is OK especially when the outside temp is 98ºF. It's when it gets past 235ºF that you need to worry.

If you are wondering about the difference between idle and highway then consider the fact that the thermostat is restricting the flow of coolant. Thus, as you increase the RPM of the engine it will create more heat, but there is some point at which the thermostat is restricting the flow to the extent that you can't pump enough coolant through the system to cool it down.

You could always do a test and remove the thermostat and see if it cools it down.

 

I do recall somewhere in the archives that people discussed drilling holes in the thermostat to increase coolant flow. May take the stat out and give it a try, would be a "cheap" fix!

Thanks for the post so far.

 

My 1980 does the same thing, though only with the AC on. On the highway with AC on the temp goes right up to 220 turn the AC off and it goes back down, slow down it goes back down. I'm not sure where the issue is. Is it an air flow problem at high speed when the Fan does not work or is just that the cooling is not enough for the extra heat at high speeds. ???

 

drilling the tstat is done to help get the air out of the system, not increase coolant flow