I have a 1979

 

Try this
c3 corvette overheating corvette forum

 

Yeah, the year definitely is needed to help diagnose but we could use more info!

• First post a couple pics from each side of the engine compartment without the air cleaner – make sure to include radiator to distributor.
• To what degree is the overheating & what symptoms tell you it's overheating?
• Is it during idling & stoplight traffic, highway driving, all the time?

 

You're just going to have to dig-in & go through a de-bugging procedure and rule out things item by item. Highly unlikely anyone online tossing out scatter-gun ideas from the hip is going to be able to solve the problem. Could be one of many things, or a combo of several, added up. Probably a combo of several. The top items would be Thermostat/Radiator/Blockage/Poor fan draw (missing seals, no shroud, fan sticking too far in/out, etc). Go through the following list. Check the items off one at a time in a methodical way:

1) Thermostat: Is it working...installed backwards, etc. Put in a pan of water you heat up and observe what happens at a certain temp.

2) Heat Transfer: Is your radiator plugged up internally or externally? Look carefully with a strong flashlight. Sometimes you can't tell if there's 40 years worth of dry bug and moth parts...and tiny stones trapped between the condenser & radiator. You might pull the radiator out and clean between ...and make sure the condenser is clean of debris too. And put some rid-lime or another product inside the radiator if it's mineralized inside (Only use distilled or de-mineralized water upon refill).

3) Is the fan clutch (if it has one) working fine?

4) Belt: Is the belt too loose or glazed ...and slipping?

5) Seals: Are the radiator seals (very important) missing? Or ill-fitting? Lot of guys throw these away and the fan will pull air from around the shroud and only a partial amount *Through* the radiator. Those seals need to be in place. Companies sell kits for them. It's common guys through them away...and don't understand their importance.

6) Is there a spring in the lower radiator hose to prevent it from collapsing as you drive (sucking in on itself...choking off coolant flow)??? Squeeze it and make sure it's firm.

7) Are there bubbles or combustion smells in the coolant reservoir? This could indicate a leaky head gasket. They can eventually rot from age and cause leakage which can lead to overheating.

8) Is the engine running fine and the temperature sensor is just flaky? Ohm it out and compare to a coolant/resistance chart for your car. Maybe it's not actually overheating but the sensor says it is.??

9) Water Pump: Sometimes these flake-out too. The impellers can spin on the shaft. It's the least likely thing...but if all else fails, consider replacing it and make sure the new one spins in the right direction (not reverse).

10) Misc... Other items could include: A crappy flex-fan, plugged other hose, kinked hoses..too low on coolant, Off-timing, fan not positioned in the shroud the proper amount, etc. Hopefully you already ruled some of these 'basics' out. But don't overlook them!

Well, those are the main things. Make sure all the basics are good...you could have 3 issues coumpounding the problem. You most likely don't need an Aluminum radiator (bad idea anyway), or electric fans (no free lunch on heat rejection). Those would be just making larger issues. Avoid interweb "miracle cures", save your $$ and go through the list item by item and get the stock system, EACH component clean & working like they should be ...if your car is mostly stock. Get busy and you should get it ironed out soon enough. Good luck.

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So I had an issue with overheating on 02 vet, I pulled over and the coolant was bubbling. Parked it at a friends for the night and went back to check it later. Noticed the coolant was low. So at this point it was running extremely hot at idle. I drained the coolant and recharged the coolant which I did not need to do. I topped up the coolant and ordered a thermostat, water pump, rad cap, and relay for the fans. I should mention that when I started the car again only the one fan behind the rad would turn on (radiator fan) not ac fan. I went right to the fuse box and checked my fan relay switch and the Maxi fuse associated with the fans. Which the maxi fuse was Broken. I got a new 30 amp maxi fuse and put it in. Solved everything. So all it was that was causing the over heating was when I was at idle and my engine was getting to the point where the fans should turn on and keep the coolant cool in the rad, they weren’t turning on which was causing it to overheat. Simple 5$ fix so deffinitely check fuses and relays first would be my suggestion before diving deep. I hope this helps somebody!!!

 

Based on all the information you provided, I am guessing it is the mufflers.

 

as the above poster is identified as a Pro.
Clearly, he must know!
Or,
Maybe,
We back up a bit at the other numerous suggestions.
Basically, C3 Corvette's are notorious for overheating.
numerous things can be at play. From improper ignition timing, (one of the most common issues), to a missing spring in the lower rad hose.
To the OP. if you choose to actually research this. You will find this to be a ongoing issue for many.
Everything must be right on a C3. They are far more fussy than a standard car.