1991 Chevy Camaro 3.1 V6 Cooling problem

Hey Guys I just pulled my 91 Camaro RS out of hibernation for the winter and driving it for a couple days, everything was fine. Except I noticed I no longer had AC in it. I did before winter. I should preface that the coolant gauge generally never went above about 160. I was dailying it to work for a few days (about 25 miles) and I noticed when I’d start city travel (about 3 miles through town, 20 miles on the highway and another 2 miles stop and go traffic) It would start to get hotter. The central gauge reads 220 and it would start pushing a bit above that. Never got to red or anywhere close but it would go a bit more past half. If i had to guess it was reaching 230 or so. The more I’d travel the cooler it would get. I noticed the radiator fan wasn’t running. The next part is dumb I know but I ended up replacing the relay, fan motor and the fan switch. I hate throwing parts at it, but in a rush I did. I also noticed my AC compressor clicking on and off in about 3-5 second intervals. Now the ac compressor doesn’t seem to click on at all. Now I’ve been reading that the cooling fan doesn’t come on until 238 which the car probably has never reached. That seems very hot to kick on the fan but I’m not an expert on older vehicles (I’m no expert at all if I’m being honest.) I’m not sure If I let the car heat up that much if the fan would kick on but I’m a little anxious about letting it get that hot. I suppose it’s possible it was staying much cooler because when the AC was running, it would automatically turn on the radiator fan but again i could have my understanding of the information wrong. I did check the 20A fuse under the dash and it was fine. I’m not 100% sure if the two problems are related or not. The only other thing to note is I see a cable with a red wire towards the rear of the driver side engine bay, real close to the 3 relays. It’s not connected to anything. I’m not really sure where to go from here in diagnostics. I’m not sure if I’m just looking at a bad AC compressor and the fan will work once it reaches proper temp, or if there are other problems with the fan.

I believe if you unplug the coolant temp sensor, the fans will default to on. This would be a way to test that the fans are at least operational when commanded to come on by the computer. I’m not sure where the sensor is on your car. On most GM’s, it is near the thermostat and has one black and one yellow wire leading to it.

Definitely worth a look. Thanks! I’ll give it a try

I can’t attach pictures but this was a link I found that i think shows the sensor. https://www.google.com/search?q=91+camaro+v6+coolant+temp+sensor+location&tbm=isch&source=iu&ictx=1&fir=mPdCyOVY5PfakM%3A%2CDiGEVFokJf70rM%2C_&vet=1&usg=AI4_-kQ3Pg4lEG3WeQHWvAN4YOdno5P0CQ&sa=X&ved=2ahUKEwjqyr2fjNDhAhXmYN8KHeifATsQ9QEwAHoECAgQBA#imgrc=mPdCyOVY5PfakM:

Well, I definitely pulled the right sensor because the temp gauge went to max. the downside was the engine wouldn’t start with the sensor unplugged. The fan wouldn’t run when the car was in the on position. Not sure if it was supposed to or not.

Ok further update. Probably not a super smart move but I connected the fan and pulled the sensor while the engine was running. it of course stalled out but not before the fan kicked on ;). So my theory is that the fan is fine…probably was. But the temps were remaining cooler because the fan kicked on more when the AC compressor was running or trying to run and now that the compressor is dead, the fan doesn’t kick on as much. My only concern/ question is if it does wait til 238 or so kick the fan on. am I in danger of overheating or is this just normal? I feel like that’s really hot to let the engine get to.

The coolant temp sensor is the one sensor up near the thermostat with one black wire and one yellow wire. Usually when you unplug it, the idle will go up and the fans will come on. I think your compressor is a seperate issue. You said previously the compressor was short cycling, so it was probably low on freon. I imagine now it may be too low on freon to come on. I’ve read about the GM cooling fan strategy before, but I can’t remember everything about it. I remember one fan is commanded on at a certain temp, then both fans are commanded on at a higher temp. And both fans are commanded on when AC is on.

I just looked it up, low speed fan (or single fan) commanded on at 208 degrees. High speed fan (or dual fans) commanded on at 216 degrees. This is for a 2005, though. I imagine, but am not certain, that the fan strategy is similar for all GM’s equipped with electric fans with the 3 fan relays.

I read your original post again and you mentioned replacing a single relay and a fan switch. I think the older system must be different than what I’m used to and describing. At some point they went to a 3 relay system and the computer acts as the switch by providing a ground to the relays.

From what I can tell for vin T, F, and 8 engines, the primarily control for the radiator fan the ECM, which turns it on at 220 deg or when the AC head pressure is over 230 psi and the vehicle speed is less than 40 mph. There’s a backup to this – if the ECM doesn’t or can’t turn the fan on – on the V6 a redundant cooling switch turns the fan on instead.

On vin E engines, the ECM is’t involved and there’s only a coolant fan switch, which turns on at 240 deg and off at 215 deg. The AC can turn the fan on also. Note that the dash gauge may not read the coolant temp in the same place as the ECM or fan switch does, so there could be a discrepancy due to that.

Freon might’ve leaked or suffered from the winter months. The temp gauge shot u p to max when i unplugged that sensor it does have a black and yellow wire so idk if there’s different sensor or not.


So based on this it’s the former. The fan should turn on at 220 which ion my gauge is dead center. So if I understand properly, even if the problem was my computer, the fan switch which is brand new should kick the fan on. Maybe there is an issue with the gauge considering unplugging that sensor did kick the fans on. then again maybe my coolant sensor is bad.

Yes, appears to be a T engine. 8th position of the vin is the engine code for chevy of that era based on this link.


Check the connector for the coolant temp sensor used by the computer, maybe it isn’t making a good connection. Where the sensor screws into the cooling jacket. Also with the connector disconnected, measure the resistance of the sensor. Should be in the range of a few thousand ohms. Is it?

Poo, I was going to say oh i’ll just recharge the AC system until I remembered that this is a near 30 year old car and R12 isn’t as easy or cheap to get -.-. Maybe a project to wait until after I swap in a 350 SBC. That’s what T-Tops are for lol.

I’ll investigate that further. I’ll need to find where the ECU is. Hopefully somewhere relatively easily accessible.

I used to have one of these, same vintage. If I recall correctly, there are separate devices for coolant sensing; a switch to activate the fans and a sensor to drive the gauge. My memory may be wrong so best to check for sure. Just wanted to point that out in case it is relevant. Do you still have the air dam on the front? These get knocked off a lot since they hang so low and scrape on steep entrances and the car will tend to overheat if that air deflector is not in place.

I’ll have to look.

You should edit out your VIN . It is not needed and may not be a problem but why put that kind of info on an open web site .

Didn’t really think about it. Thanks for the headsup.

I believe you may be correct that there are two seperate sensors, an engine coolant temp sensor (the one I’m discussing) and a seperate sensor for the gauge. I seem to recall it was that way on the 350 of the same era, at least. The one we’d be concerned with is in one of the photos, right by the thermostat - one black wire, one yellow wire leading to it. If unplugged, fans will come on (on a 2005). The older 350’s didn’t have electric fans (on the trucks, at least), so I can’t say for certain that fans would come on in a 1991 GM with e fans if you unplug it.

I do not have my air dam as it turns out. I will look into one of those. At this point In terms of everything else. It’s hard to say if the car is acting normally or not. I haven’t gotten it hot enough to see if the fan would eventually turn on or not. Obviously it kicked on for a moment when unplugging the coolant sensor. I know it’s never gotten so hot that you can hear coolant boiling.