alright the car isnt overheating. but it gets very hot... right around 3/4 temp.. well maybe about 220? the thermostat is opening ive tried 2 different temp thermos... the car stays at about 200. if i drive it for about 20 min then park and let it idle the temp will start to go up. i know the thermo is opening because im taking the temp on both the upper and lower hoses and you can tell when it opens because the temp almost equals or within 5 to 10 degrees. is it that the stock fan isnt pulling enough air? if so is there a good replacment without going broke with a good electric fan set up. ive seen those get up around $500 with a coolant temp sensor and the works. im trying to keep the cost down but ill do what i have to. Right now im fearing traffic .

 

It sounds like your not moving enough air. There are some basic things to look at. Make sure the radiator seals are in place and in good shape, there are seals between the radiator and core support, core support and hood. The fan clutch my be worn, it should only turn abour 1/2 turn when you shut the motor off. The fan shroud should fit well against the radiator and the fan should be about 1/2 way into the shroud. Make sure the air dam is in place although it has nothing to do with it getting hot at idle.
The lower radiator hose might be collapsing, make sure the spring inside it is ok.

 

Running too warm at idle is usually an indication of a fan problem. Running warm along the road is usually a radiator problem. Of course there are other variables. I would first confirm that your gauge is accurate by using an IR gun. These car don't need these electric fans. They only mask the underlying problem. You may need a new clutch fan.

 

If original, the radiator probably has really high cholesterol.

Look inside it and if you see any build up, I would just replace it. I'm running a decent amount of HP and have no heat problems at all with a stock replacement.

 

Right now I'm running the Flex-a-lite #210 rated @2,500 cfm's and I have been borderline with my temps but they just came out with a 3,000 cfm dual 12" and I will be switching to that one soon.....After speaking with there tech. he said that extra 500 cfm will make a big differance n will do the job so we will see...............Jerrylee///

 

Make sure your timing is set correctly - set it up for 36 degrees total and make sure your vacuum advance control unit is operational and hooked up to manifold vacuum. Inadequate timing and/or inoperable vacuum avance will cause the symptoms you describe.

 

Hey I just got a 76 corvette and experiencing the same running hot symtoms. I was wondering if you could describe what the "vacuum advance control unit" is and where i could find it in the car.

thanks

 

the vacuum advance unit is attached to the distributor and is a silver cannister with a vacuum hose plugged into it.

Here is a pic of the distributor out of my '65 with the distributor cap removed and the vacuum advance unit is the silver unit on the left side of the photo.




The HEI distributor would look slightly different with the cap off but the vacuum advance cannister will look the same and you should be able to see it by looking on the passenger side of the motor where the distributor is sticking out of the distributor shielding pointing kinda towards the front of the motor which you can see here to the left of the breather tube coming out of the passenger side valve cover on my '78:

 

74vette454

changing the t-stat will not lower your operating temps, the t-stat only controls the MINIMUM operating temp your car will run at, not how high it wants to run.

At idle or low speed driving cooling issues are usually from airflow or timing problems.

1. airflow: check to make sure the fan clutch is operating correctly and all radiator seals are in place.
2. Timing: as Lar's already mentioned, make sure your timing is correct, that the vacuum advance unit is hooked up, connected to a full manifold vacuum source, and working correctly.

BTW, 200º-220º is NOT really running hot at all. The stock t-stat on your car from the factory was a 195º unit and with that the car would run in the temperature range you describe. My '78 is still all 100% fully stock with all the emission equipment still installed and the factory 195º t-stat. the car runs 200-210º regularly and with AC on on a very hot day can go to 220º.
That's perfectly normal and expected on these cars. With the emissions equipment the cars were designed to run in these operating temps as it helped lower emissions levels
If all the emissions equipment is removed from your car and you lower the t-stat to a 180º unit (leave the 195º unit if your car still has all the emissions equipment) than your car could run at a lower operating temp if the rest of the cooling system is capable of removing the heat but be aware that even if all the emissions equipment was removed from the car and you changed out to a lower 180º t-stat the operating temps will most likely stay the same unless you change the timing in the car as suggested by Lars because as stock from the factory the car had somewhat retarded timing levels (again for emission purposes and the goal was for higher operating temps) and your vacuum advance is probable connected to ported vacuum rather than full manifold vacuum.

 

Completely agree w/BarryK on this. It's my third summer to do the work commute (40 mis. round trip daily) and we've already been over 100 degrees air temp. a couple of times here this year. The hotter it gets outside, the higher the indicated engine temperature.

I've even seen a 10 degree change (width of a 0) on cloudless days between driving on unshaded and shaded pavement when it's really hot.

 

They're also adding alchohol to the pump gas these days......., which will lean you out a bit causing you to run a bit hotter. Newer computer controled cars will adjust timing and fuel mixture but the older ones won't.

 

Read Barrys reply for a excellent answer to your problem and the normal charactisics for later C 3`s. ...

 

best answer so far