I have a 1986 Corvette and I’m dealing with overheating issues. If I idle for too long or I’m sitting in traffic for too long it overheats. But as long as I’m driving at a decent speed, it is fine even with the AC on max.
It has a single fan (wired to stay on all the time but that’s another issue) 165° thermostat. New radiator cap new fan motor. debris is cleared from the radiator. I used a headgasket leak detector and it showed there to be no combustion gasses in the system. I really don’t believe it is air in the system because i have bled it many times.

I did notice that the center air dam is missing however I would think that that would only affect it at speed.however it works good at speed so i don’t believe that to be the culprit.

I don’t believe it would be a coolant flow issue because i would think that would have issues more so at speed than at idle. Would this be a bad assumption?

 

What coolant temperatures are you seeing

 

Ok debris free under the bumper, what about between the AC and radiator I have seen the fins be Furry and Tons of junk in between. You can get a glimpse through the passenger side where the AC lines go in.

You can also clean the fins with an AC cleaner you find at Lowe's or Home Depot

 

yes that is what i meant by its clear. I took the radiator out and cleared everything a couple times now.

 

When you say overheating what temperature are you getting up to? Is it actually boiling over ?

 

If it cools down that well when moving your cooling system isn't the problem, it would be an airflow issue. You say the fan is wired to stay on the whole time so I "assume" you've confirmed that it is running but how much airflow are you getting. I know you don't have a meter for that but is it pulling a lot of air?

I'm with the other people in wondering what temps you are actually seeing. For instance, you have a 165 degree stat in the car (which IMHO is too cold) but your not going to see that while sitting still unless you have some serious fan air movement or it's super cold outside. These cars run warm. For instance, 220 isn't over heating, that would be a normal temp to see in a stock car that is stilling still until the fans would normally come on but a lot of people will post that their car is overheating at that temp. Not saying the case, but why we are asking as it may just be an expectations thing. So, if you are chasing 160, 180, 200, etc while sitting still, you will be chasing your tail, especially with only one fan that is wired to be on all the time.

 

My thoughts exactly.

It seems to me like it has good airflow but without a meter there really is no way of telling. I replaced the motor with a new one as well.
Perhaps though, when the person who wired the fan to stay on always did that they made it so it doesn’t get enough power somehow? I will have to measure the voltage it is getting there.

I agree, I also have a 185 degree thermostat I plan to put in once I get this problem sorted out but when I put it in right now it just makes all my temps go up faster so I cant sit in traffic as long.

I understand that these cars usually run hot between 220-230 stock if my car never went above 230 I would be happy. However if i let it the temps will rise and stuff starts breaking. With the way my car is currently (super cold thermostat and fan wired to stay on all the time) you would think it wouldn’t easily be able to even get up to 220.

Also It isn’t ONLY one fan this car came with one large fan instead of the two smaller ones. lots of people seem to think they all have 2 fans and that is the problem when that just isn’t true. — just to clarify.

 

How did you clean your radiator? You really have to have it out to clean.

 

What is the car getting to now that you are determining to be overheating?

What you've stated is actually a really common misconception, if I'm understanding what you are trying to say correctly. A colder thermostat does nothing with the max temperature of a cooling system or prevent a car from overheating or running hot if it was running hot before. There is zero difference in max thermal cooling between a 160, 180 if the natural temperature of the system is above 180 degrees. The thermostat just controls when the cooling system will open and start cooling the system off and what the minimum running temperature can be.

I'm not sure about your comment about the fan though. All 1986 Corvettes came with a large fan on the back side of the radiator. Some cars came with a small pusher fan that goes in front of the radiator but that only came on HD cooling package cars like the Z51. Not trying to be argumentative but I'm trying to understand what was done to the car. If the PO said it had 2 smaller fans and they put one larger fan on it, then someone has been doing more mods to the car than I expected. If that is the case, is the fan shroud still stock and the fan bolted to it? If not, what does the shroud look like (can you post a picture)? If it's a fan just attached directly to the back of the radiator with the shroud removed (what I'm now envisioning), then I think we just found your problem. That would kill the efficiency of the fan and the radiator but is a common "mod" people do to think they are reducing restrictions and increasing air flow but it actually reduces the ability of the fan to cool the fluid while at rest.

Also, for the fan. If it isn't stock can you grab the part number or advise on the fan specs? It's possible it has a low and hi speed wiring system as well as it's possible it just has a lower CFM rating.

Hard to diagnosis these things on modded cars without seeing them thus all the questions and sometimes "assumptions" I'm making :-(

 

yes i took it out completely and made sure it is completely cleared and i can see daylight clearly through the fins.
I haven’t done the same with the ac condenser yet because I don’t have the equipment to evac/fill the system. I just ran a hose through it while it was still in the car

This is the front side of the ac condenser. Ive done my best to clean it while in the car but not sure that is enough

 

If i let it will get past 140 but I usually let it get to 225 then turn the heater on and if it then climbs much above 230 i will shut it off. Is this the info you were asking for not sure if I answered your question very well.

I understand this. What i was saying mainly has to do with the fact the fan is wired on always; meaning that it should keep the max temperature down.
from what I understand the thermostat controls the minimum operating temp and the fan should control the max.

Sorry for the confusion. It is still the stock single fan. I was just clarifying that because in the past i have had people telling me it is supposed to have the 2 small fans instead when that is simply false.


It should be noted that this is not a z51 car and therefore does not have the pusher fan

 

Thanks for the clarification as that does help. Looks like a stock fan and I would agree it's running hot if it's getting to 230 with the fan on full time, especially in Utah. I know it can get warm there too but I'm guessing you aren't seeing 100+ degree days like I get often.

If you took the radiator out completely and cleaned it, you would have diffidently caught the main concern others have had. These cars tend to be vacuum cleaners and suck up all kinds of junk that gets stuck between the radiator and condenser. Sounds like you are covered there.

Diffidently starting to run out of thoughts though. But just going through the things in my mind that I would if it was my car and I was trying to diagnose things.

When you cleaned the radiator, did a bunch of scale come out of it? Did you look inside and notice corrosion? I still think it's an airflow issue since you say it cools down when moving and only gets hot while sitting at idle, but it could be a low flow issue due to restrictions in the system or a bad pump (old belt). If some of the cooling vanes in the radiator are corroded then it wont be cooling as efficiently, but the added RPM of the pump (more pressure/flow) and added air movement could be why it's cooling while driving. I fought that with my Viper which was the case that my radiator had dead sections due to being blocked. Apparently a common issue on early Vipers :-( New stock radiator and I no longer had overheating issues while at idle or driving.

Your overflow is at the properly level, correct? Just asking to make sure it hasn't gone dry and there may be some air in the system.

Age of your waterpump? I honestly don't know how to test for flow on them.

Really just drawing at straws with most of the above. I still wonder about the fan speed since it's direct wired but I would assume it's pulling enough air if getting full voltage.

 

Have you done a pressure test of the cooling system? A few years back mine was running warm even with a new aluminum radiator. Ended up being the heater coolant valve was leaking when it was above idle rpm. Put in a new one and it held pressure again and ran at 184, would hit 192ish at stop lights.

That condenser is pretty banged up blocking air flow