Hello all (It was suggested I post here for more replies),

I just bought my first corvette in April a 91 coupe. It has been a lot of fun and great joy to drive. I have always wanted a Vette and I finally got one. But now that it is summer here in the mid-west, I am having a problem with my temp gauge.

Back in early June, I was sitting in traffic that was backed up because of a train crossing. I happen to look at the gauge and noticed that it was close to the max temp line. I was really concerned but there wasn't anything I could do as I was trapped in line. However, when I was able to start moving again the gauge went back to the mid way point, so I didn't think much about it. At no time did steam come from under the hood.

Not long after that, the low coolant light would come on when I started it up but then go out. I thought this was odd as I had just had the oil changed in May and I know they filled the fluids. But I thought maybe I needed anti-freeze so I bought some but didn't put any in.

I didn't have the problem any more so in the middle of June, I took a road trip with it and everything was fine. During the weekend, I was on a hot road again sitting in traffic because of an accident and you guessed it, the temp gauge started rising again to the max line. As soon as I could, I got out of the line and started driving and like the last time then gauge went back to the mid point where it always is (again no steam).

When I got back to the place I was staying at I checked the coolant level and it was full. So I didn't know what was going on. Last week I took it in to have my wheel bearing fixed and had them look at the temp problem. The problem stumped them. They replaced the sensor first, then the T-stat, checked the internal temp of the engine and found it was within specs. But the gauge still rises up to the max line when it sits for a long time without moving.

The shop manager said they called some people in CA that have the same series Vette and they told him that it is normal with that year of car. Because engine sucks the air up from the ground, it is getting all that heat from the road. Well that kind of makes sense but I am not a mechanic so I don't know if this is really the problem.

I was checking this board last night for someone with a similar problem and found one. In that some of you thought, it might be a relay problem. So I don't know. What do you all think? Oh, BTW, the fans come on just fine.

Keith

 

Not sure on 91 but on my 96 turning the a/c on forces both cooling fans on & lowers the coolant temp a lot. YMMV.

If yours has the digital temp gauge use that, the analog is only a rough estimate.

 

DISREGARD ANALOG GUAGES ALL TO GETHER ,NONE OF MINE ARE ACCURATE, ALL MY DIGITAL ONES ARE DEAD ON!!!

 

Turn the heater on full blast when you are in this type of situation. It will bleed some additional heat off and lower your coolant temp. That will keep it from overheating until you can get moving again. It sounds to me like your gauge is working. You could have some blockage in your radiator that is affecting its cooling capacity, but I doubt it. It's probably just what you've already figured out, additional heat from the pavement, less air movement so hot air is trapped under the hood, etc. It shouldn't hurt to go up over the boiling point on occasion. I've had cars do this many times over the years. Sometimes there is a problem, sometimes not. Keep an eye out for coolant leaks just in case.

 

Given the age of the car, the radiator is probably full of leaves and other garbage and needs to be cleaned. From the passenger side of the radiator, you can use a flashlight to peer into the shroud and look to see if it has a lot of junk build-up. Also look at the front of the a/c condensor to make sure the face of it is clean as well.

 

Look at the digital guage as stated above. Mine needle would touch the red zone in traffic / summerheat / no AC on. If you turn the AC on the temp should drop. The digital guage shouldn't go over 232 ish before the 2nd fan kicks on (no AC on).

 

You may not actually need to, but on a 91 you can buy a sensor/switch and wiring harness that will turn one or both of your fans on at a lower temperature. That way you won't have to turn the air conditioner or heater on when stuck in traffic.

 

What he means is, the space between the radiator may have all kinds of junk in front of it betw. it and the condensor. For all you know, some of the fins of the radiator itself may be just slightly turned so that they aren't allowing max air flow and thus, cooling as efficiently as possible. Do the first thing tho, and look for junk in between.

 

All of the above, plus: Your radiator is a heat exchanger. The heat energy transfers from the water to the aluminum radiator core and from the core to the air. If there is little or no fresh air passing through the radiator core, the heat transfer from the radiator will be severely inhibited. That is why cars have fans. Just as you enjoy a nice fresh breeze on a hot summer day, so does your car. You may wish to check that your fan(s) come on as they are supposed to at the proper temps. Higher temps at lower and no speed are normal and more a matter of air flow than the heat of the pavement. It will run warmer if you let it idle sitting on the nice cool lawn, too. Other than checking for problems, maintenance is the key, with C4 cooling systems. Check the fan operation, clean out in front of the radiator, and flush and change your coolant on schedule and you will have carefree cooling. Without a report of specific and alarming temps, I am not convinced there is a problem, here.

RACE ON!!!

 

As everyone said, that's normal (but un-nerving). If everything is clean, reprogram or buy a manual switch to turn your fans on earlier. I'm in a really hot climate, so I went with a larger aftermarket radiator (Ron Davis). Today it was 115* outside, but my coolant temps stayed around 205*. Yesterday, I got stuck in traffic and I saw 220* for a few minutes. With my stock radiator, I wouldn't drive the car if it was over 106* outside, because I would run around 230 - 240*.

 

Thank you all for the advise.

The radiator was cleaned out while it was in the garage. But that didn't fiix the problem. The manager said the same as you all that is the way it is. However, an instructor for our local Jr college that teaches Heating and A/C, overheard me talking about the problem and said that it shouldn't be doing that. He thinks the radiator needs to be cleaned out as in taken to a radiator shop and boiled and the cooling system flushed. I can't tell you when the last time the cooling system was flushed. I guess I should ask the other owner, he works close to me.

The instructor also said that he thought that the intake manifold is clogged.

Any ideas on this? I am at a loss. The other day I got stuck in traffic on the highway (moving to one lane) and there was nowhere to turn off. So I was just praying I would make it out of there. It was really hot that day so I had the a/c on and it didn't reach the max point. Now I wasn't sitting still a lot kind of just rolling along. So some air was moving.

Well again thank you all for the advise.

P.S. (A new water pump was installed Apr 04, it has a low restrictive air induction coupler (what is that), and a K & N air filter) The other owner did tell me that he put on an after market air filter over the radiator to increase the amount of air coming in, guess this only works when the car is moving.

Keith

 

First, glad to hear you're enjoying the car, less the temp issue.

Adding to what has been said, at idle, turn the A/C on. Get a flashlight and check your primary fan(left side fan) and secondary fan(right side), both fans should be turning. I've experienced the same problem as yours and the primary fan had failed, leading to higher temps at idle with zero movement. The single fan is not sufficient to cool the engine under these conditions.

CFI-EFI gave a good primer on thermal transfer. The C4 cooling system, at maximum efficiency is, ahhhh, adequate. With the slightest problem, you will get a rising analog temp. If you elect to get a scanner, you can check the computers look at the temp sensor and compare with the analog gauge.

As a note, I'd sell some furniture and buy the factory service manual. The sections on trouble shooting are quite helpful. These cars have lots of gadgets. When I first started driving my 90, I thought my hearing got better past 3000 RPM. Then, I read the owners manual, Speed Volume Control. Darn.

Let us know.

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