The relay I have hanging there shoul be the one for the fan if I’m not a total dingus…my track record isn’t so great at the moment.
Ok so this random red wire? You guys have a clue what this is for?
The coolant temperature sensor with the yellow and black wires is monitored by the ECM under the right side of the dash. The ECM grounds the dark green/white wire to the fan relay to switch on the fan based on coolant temperature and A/C operation.
The coolant temperature switch with the dark green/white wire will ground to switch on thew fan relay, that is a redundant coolant switch to prevent over heating.
That was very helpful thank you…now I just have to find where the fault is which is causing the fan to not turn on.
One test you could try is to connect the A and B terminals of the ALDL the same way as retrieving diagnostic codes. Then, when you turn the ignition switch to ON, the system will begin flashing out the diagnostics codes and at the same time, enable the fans to run…
Worth a shot. If the fans don’t come on, we know there’s either a wiring problem or the new fan motor is poo.
I had the '77 Z28 350 and it was fast as light, Holley carbs, glass packs, I could take it to 140+ mph, scratch even beefy new tires from a stop, glass moon roof, I could take most any car that
pulled up to me…easily. Old Days!
How is this going? First, I didn’t read the most recent posts but did you replace the thermostat? Next, don’t worry about overheating if you are only getting into the low 220-230 range, my V8 was regularly around that, older car your water pump will be questionable (it can be working without working “well” understand) Your ECM is probably either behind a kick panel by the passengers feet or pressed against the firewall under the hood on the drivers side. Spend the $35 and top off your freon, you have a leak, but not worth the $400 to replace your ac compressor, pay attention to George San Jose, that guy has pulled my car back on the street with his advice several times, Mustangman too. I’m no expert, but I’ve had every cooling system problem known to man, bad stats, bad sensors, water pump[ clogged radiator fins, cracked rad hoses, damaged air dam, (yours is missing? deal with this part when you can at a Pick Ur Part, no more than $30)
Sorry I’ve been busy wtih about 30000 other projects over the past week. Here’s where we’re at. I got an air dam but haven’t installed it yet. I drove about 2-3 miles from the dealership to my apartment and it went beyond max on the gauge. so like 270 or so. However, the radiator was cold, the top radiator hose was hot. the fan did turn on during earlier tests but idk if it ran during my drive home.the drive home was maybe 5-7 minutes. that seems awful kick to have temp spikes. that high. I haven’t looked into getting R12 because i thought it was illegal now. I’m not sure if my temp gauge isn’t reading right due to some problem or if there’s a problem with the radiator not pumping properly. idk how to test this without significant risk to the engine.
That part about radiator cold but engine getting hot sounds an awful lot like a thermostat stuck closed. I would recommend making sure the coolant level is good, and I’d probably go ahead and change the thermostat. You can test them, but once I pull one out, I just replace it with a new one.
The e fans went out in my 2005 Sierra a while back. Long story, but as long as the truck was in motion over 30 mph or so, it didn’t overheat. The only way it would overheat is if I would put it in park and let it idle.
Don’t worry at all about the AC / r12 for a bit.
If the coolant level is good, you replace the thermostat, and it still seems to overheat - verify the engine temp with a handheld infrared thermometer (cheap and handy anyway).
Yeah i wasn’t worried about the AC at all. i know I’m putting another engine in eventually. I know around the last time i posted when the engine overheated and there was steam coming from the engine bay I made 2 mistakes. one, the fan was unplugged (extreme derp on my part), 2 the radiator cap was slightly losse (needed turned 90 degrees to seal). The last time I checked the coolant in the radiator was full and bright green. The oil looked clean as well. The reservoir tank doesn’t look as nice. It almost looks a tad orange and super dirty. I’m not sure why but I can take the reservoir tank ouit and clean it. I’ll definitely look into the thermostat though. They’re not super pricey and I know they’re supposed to be easy to replace.
You may have a faulty engine coolant temperature sensor, the one used by the computer. That would explain why, when you totally disconnect it, the fan turns on. But not when the coolant overheats. If that part has lost its calibration the ECM may think the coolant temp is 170 when it is really 240. That part has no moving parts so is an uncommon failure item, but they do still fail occasionally. The way to tell is to disconnect it from the harness and measure its resistance. If it is working correctly it will measure the correct resistance for that temperature. You’ll have to do some Google research to find the calibration chart, or a Chevy dealership shop will have that info. On my Corolla the factory service manual doesn’t have that calibration chart, but the Chilton’s repair manual does. Go figure. Typically those gadgets measure in the 1-10K ohm range at ambient temperatures.
Sorry I haven’t actually confirmed if the fans come on when disconnecting the coolant switch. I had run the one test by sending the car into diagnostic mode and that did kick the fan on but havent had a chance to test if disconnecting the coolant sensor turned them on. Doesn’t the coolant temp sensor send the temperature info to the dash gauge? If it does then I would say it’s fine because again, the temp on the gauge definitely shot up after a few minutes of driving.
Something I just thought of, if the top radiator hose was hot, wouldn’t that mean the thermostat is opening to allow hot coolant to go to the radiator?
I’m not sure. I imagine it would depend on the direction of the coolant flow from rad to engine and back. If thermostat is stuck, one hose would be hot and one hose would be cool, I’d think. But I’m not entirely sure which hose would be hot and which would be cool. Others here may know. Thermostats are like ten bucks and can be replaced by removing 2 or 3 bolts, usually. I’d probably replace it to rule it out.
I think on those years GM, there was a seperate temp sensor for the gauge and temp sensor for the computer. One tells the gauge the temp, the other tells the computer (which turns on the fans) the temp. Not 100% certain on that, but seem to recall that being the case on the GM trucks.
I’m not familiar with this 1991 Camaro . . .
But today I worked on a 1990s era GM big block truck . . . and it had 2 separate coolant temperature sensors
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After changing the thermostat, the Coolant Temp Sensor was my 2nd hypothesis as well, and I have had them fail on me. Put as simply as possible, you’re running hot because your ECTS is literally telling your ECM it’s running too hot, your car will do what the ECM tells it to do
That’s what I thought I recalled from the 350’s of that time period (tbi). I don’t know for certain, but would think the V6 would be the same.
Have to respectfully disagree. If the ect sensor was telling the computer the engine temp was high, the computer would turn on the fans and the engine would run cooler - not overheat.
If the engine temp sender (to the gauge) was giving a false hot reading, the only issue you’d have is the gauge pointing to hot. But no real overheating.
I’m going to say if it overheats in 2 or 3 miles, either the thermostat is failed shut, or there’s not enough coolant (or an air pocket in the cooling system). If it were a gauge problem, it would probably read hot immediately when the key was turned on.
If the top rad hose is hot, but the radiator is cold - it’s just about got to be a stuck closed thermostat.