I'm new to this forum, but I was hoping for some useful help. My friend and I have been working on a customers 74 Vette for some time and have been having issues with the engine staying cool. We have put in a new triple core radiator rated to 900hp, replaced all hoses, used water wetter with water for the cooling system and have the timing at 9 degrees, we put new plugs gapped at 45thousandths with new braided plug wires, plus a Mallory cap and rotor. Plus we have installed a pusher fan in front of the condenser to further cool the system. With the old radiator the car would idle over 200, and when we drove it I'm under 10 mins it would be almost to 260. We replaced the thermostat and radiator, now it stays very cool at idle when first started up, taking almost 15 mins to get up to temperature, but once we drive it the motor heats up gradually until it hits 260 after maybe 15 Mins of city driving. Our first thought was an air pocket but we bled the system with an open funnel for maybe 20 mins and turned the heater on. Unfortunately the engine is still getting hot. We checked plug wires to make sure they were On the correct plug and cylinder. I apologize for the long post but we are somewhat lost as to why it's still overheating. We saw on some posts online that at idle the timing should be at 18 degrees, but we are currently at 9. Could this be our problem and what is the recommended timing on the L82? Any input would be greatly appreciated!!

 

Was it over heating with the old radiator at all?

Fan clutch good, shroud sealed, air dam in place etc?
Hate to say stuck 'stat guessing youd know if it was

 

First make sure the fan clutch is working properly, with a hot engine, shut it off, the fan should stop quickly also. Make sure the foam seals are in place to stop air from going around the radiator and sealed so the fan has to pull air through the radiator and not gaps between the shroud and core. The other important item is the plastic spoiler under the front of the car. It interrupts air flow under the car and forces it up into the lower valance openings in front of the radiator.

 

Besides the suggestions mentioned above, IMO, could it be that the water pump is defective??? It almost seems like there is some obstruction blocking the flow of your coolant. The only other item as mentioned before would be the thermostat, which you replaced already. What temp stat did you install? Even when your moving in city driving the temp should be coming down, and it seems to take quite long for it to warm up. The only other thing I can think of is, even though it is a brand new radiator, could be also be defective in that the coolant is not flowing through properly.
It just seems odd about such a high temp in a C3, the ones that I have had in the past, never ran above 210 degrees in stop and go driving, (with the AC on) and when they did, I thought that was high.

Another thought, do a pressure test on the system, when I took delivery of my 75 L82, after a few thousands miles it was really running hot, and loosing coolant, couldn't figure out the problem, did the pressure test and turned out to be a pin hole size split in a radiator seam and that from the factory, brand new!!!

 

All good suggestions. Sounds like an obstruction somewhere as well. 3 core radiator rated to 900HP? Corvettes came with a 4 core brass radiator. Water pump, maybe? I have a 78 L-82 with a Dewitts Aluminum radiator with a Stewart Stage 2 aluminum water pump (180 Thermostat) and yesterday in 95 degree high humidity heat the car never went over 175-180-either idling or at speed on the highway.

 

Cracked head or leaking head gasket? I'd check the pump first. Impeller may be bad. Are you sure the sending unit is good?

 

First thing you need to do is get an IR gun and measure actual temps, particularly at the thermostat housing. I have my doubts that your 260 readings are accurate.

 

Cehck to make sure rad seals to core support with foam seals. Must have no leaks. Make sure fan shroud is fully sealed to rad with foam seals. Make sure core support is sealed to hood with foam seals. This fixed the problem on my 80 L82 with stock rad.

I now run a dewitts aluminum rad and their own spal fan kit and shroud to save weight and did away with pump mounted fan

C3 vettes must have no leaks around radiator or fan will pull a lot of air past not through rad and it only takes small leaks.

Check items others mentioned and timing.

 

The only thing I haven't seen covered here is the radiator cap. Make sure it is holding pressure in the system.

 

missing air dam or crack head/head gasket

 

Please keep us updated on you findings

 

Disregard.

Bottom of thread reply woes.

 

This build has maybe 200 miles on it. I built the engine myself. I’m not losing coolant that I can tell at least everything coolant wise is sealed I’m not smelling it in the exhaust or seeing any signs of it in the oil. Also had the heads pressure tested when they were getting resurfaced and getting shaved down to take up to a 600lift

I don’t see where it says anything on the radiator description about hp rating. Just 3 row all aluminum

 

Dcott -
You're posting in a 7-year-old dead thread. Start a new topic...

 

This is happening every week. Somebody revives the dead.

I would like to see any post more than 3yrs old automatically deleted.

 

I don't know about deleting...I bought my C3 two years ago and have learned so much even from the old threads. I would rather see a flashing indicator of some kind to notify us when the post is over so many years without any reply.

 

Agreed, I learn a lot when searching threw old threads

 

Agree too...im new less than a year...
with that said if the moderators could set the default to not scroll into old threads that would go a long way to help..
also for whatever reason i get much better guidance from google to corvette forum than searching the forum itself..

 

it was an honest mistake I was attempting to reply in my new topic but well read right on through mine into this one

 

Go to USER CP and EDIT then change the Related Thread option, and this will not happen when you are signed in.