I have a 79 that is having cooling issues.

What was usually happening is from a cold start, it would heat up and the gage would get to about 280. As soon as it hit this maximum, it would then start cooling and move back to about 220. When running, the gage would stay at 220 and if idling at a light it would creep up to about 230 or so. If I would run at highway speeds, (3k rpm for 20 minutes or so) the gage would stay at 220, but when I got off and it idled at a light, the gage would read 240 and start running warmer at 230.

This was the pattern until the last time I went out. Now from a cold start it heats up to 280 and does not recover. When I hit a light and it idled, then it would cool down to 230. When running it heats back up again. Needless to say, that was a short trip.

There is no water in the oil.

I have taken it in twice to my local Corvette shop for this issue. Here is the work that has been performed:

• Clean, flush and convert A/C
• Replace heater core
• Replace all belts
• Replace thermostat (I have had both a 180 and 195. The 180 ran cooler, but the symptoms were the same)
• Replace sensor
• Replace radiator
• Replace manifold gaskets

I was told by the mechanic that performed this that when the engine was checked using a IR sensor, the temperature was about 5 degrees less than what the gage was showing.

When running at temperature the fan engages and runs normally.

At this point I am at a loss. The only thing left is the water pump, which when I brought it in the first time I thought was the issue. I am not sure if what to think of my mechanic, although popular opinion with the wife is not favorable.

I am looking for the end game in this. While I think it is likely the water pump at this point since there is nothing left, is there anything else it can be? Is my mechanic competent and taking reasonable troubleshooting steps or did I just get a learning experience?

Thanks for your assistance.

 

first the stock gauges are known to not be accurate, I am sure someone will chime in about how to test it and install the resistor to correct the issue. Contact Lars here on the board to get his carb and timing papers to ensure it is correct. Another thing is to make sure the coolant is full, alot of times a leak or incorrect procedure filling will cause issues.

 

At idle the fan engages and runs normally. Electric fan? From what? How well shrouded and sealed to radiator? You sure it isn't blowing the wrong way? Rule of thumb is if it heats up at idle it is a coolant problem. If heats up at speed it is an airflow problem.

 

If the fan is a clutch fan it should be verified by your mechanic that it is working properly.

Do do you know where the t8ming is set? If the initial timing is too retarded it will always run much hotter. By design the timing was retarded in the 70s to make the engine run hotter.

it sounds like despite the thermostat being changed that the new one may be faulty or have pretty restrictive flow. Look into getting a parallel flow thermostat. Google it and see what the advantages of running one are.
https://www.jegs.com/i/Mr.+Gasket/72...yABEgKuH_D_BwE

 

Were the hoses replaced when the radiator was replaced? A collapsing hose will cause overheating issues.
OC Cali can be a hot area of the country so the cooling system needs to be in good working order to keep that engine alive.
Ensure the clutch fan is working properly. If the clutch never engages once the temp is up at idle the car does not pull in enough air. Also, moving at speed will help keep the car a little cooler when the fan isn't doing its job at idle speeds. If it can still somewhat cool while running around for the most part I think the pump may be okay. But that is just a guess without a flow check.
Ensure the rad has the proper sealing around the entire area to ensure air gets pulled through the rad and not around it. This is vital with cars with A/C.

 

Starting with the basics....

C3's are 'mouth breathers'. Air is scooped up under the front end and then goes through the radiator.. For air to be 'scooped' a lower spoiler needs to be in place. From there it needs to go through the radiator. If the radiator isn't sealed to the radiator support all the air will go around the radiator versus through it. At low driving speeds the fan pulls air through the radiator. A shroud ensures the fan pulls air through, with out it the fan will pull air from the engine compartment.

1. Does your car have the lower spoiler?
2. Is the radiator sealed to the support. This can be visually seen or do it with a flashlight in a closed garge.
3. is there a fan shroud? Is it sealed to the radiator. Again check it with a flashlight.
4. Is the fan properly spaced? I don't remember the exact dimension but roughly 1/3? 1/2" of the blades width should be inside the shroud.

Everyone else has posted very sound advice. Thermostats can be checked with a cooking thermometer and pot of hot water. 'High flow' thermostats allow for more more flow.

 

Bad head and/or head gasket. Have your mechanic gas check the cooling system.

 

I this were the case it should be puking water out of the radiator into the expansion tank, to the point that the tank overflows.

 

All of this plus the mentioned lower hose check. I like a high flow pump on these because they need it....Flow Cooler, Weiand and Edelbrock all make good high flow pumps.
Always drop your stat in a pan of boiling water, this saves buying a new one if it is good and saves the fact that a new stat can be bad! If it opens....its good! the wife has watched me boil many a stat, and because I am a good cook, she says nothing

Jebby

 

Not really if it is making steam pockets in the heads and block.

 

Thanks,

The fan, and fan clutch are original. The shroud is in tact and in place. Had to check to make sure it is not blowing the wrong way and it is blowing the correct direction.

 

I will take a look, thanks.

 

I will check the hoses, but most if not all have been replaced as part of the process.

 

1) Yes.
2). Exactly what would I be looking for here? Checking would be easy.
3) Yes. I believe it is but may not know exactly what I am looking for.
4) Looks like only 1/3" of the fan is outside the shroud.

 

I hope not. When I take it in again I will be sure to mention this. Thanks,

 

2. The forward side of the radiator should have a thick foam seal that closes up the gap between the forward side of the radiator and the radiator support.
3. In post #11 you confirm it has a shroud. The outside perimeter of the shroud should be sealed with foam against the radiator4.
4. 1/3-ish sounds right.

In the pic below (I'll upload it later) the red shows the gap across the top between radiator and support. Green is one of the side seals. There should 1 bottom, 2 side and 1 top seal. Blue line is air flow path without seals. Air will take the path of least resistance, going over the top of radiator versus through it. In addition there should be support to hood seal.

 

It did do this once when I first got the car. Nothing since.

I do get a few drips from the system. Mostly from the right front. It takes a day or two to show up after I run it. I have taken to parking in distant dry spaces to check for fluid leaks. Nothing is there when I leave.

The coolant level is full.

 

While I was checking all of the items, I noticed that the A/C compressor looks like it is leaking. The hoses underneath have coolant on them as well.

I have not run the A/C since the conversion, mostly because of the cooling problem.

Is this relevant?

 

Nice corvettecentral article showing the seals: https://tech.corvettecentral.com/201...-installation/

 

Thanks for this. All the bolts are there.