1987 Rad Fan
Thread Starter
Racer
Joined: Sep 2014
Posts: 421
Likes: 34
From: Troy Michigan
1987 Rad Fan
Hello, My car runs pretty hot, as do what seems like all the l-98s. Well my rad boost fan will kick on when it gets too hot around 228 but my main fan, that runs with the ac, does not. I know the fan motor works because I jumped the ac pressure sensor switch and it came on... but it doesn't seem to run when the car needs to be cooled. I am guessing its the relay, but what else could cause this? and is there a temp sensor I can replace to get my main fan to come on at a lower than spec rating? I HATE that this car runs so hot, it stresses me out. Thanks guys always appreciate the help! Also is there a way to jumper that relay to test? thanks! I hate throwing money at the car without knowing what I need!
Melting Slicks
Joined: Jan 2014
Posts: 2,192
Likes: 381
From: Lunenburg MA
The main fan comes on at 225F. The aux fan (in front of the radiator) comes on at 245F and is controlled by a switch in the driver's side head. If you ground that switch, the fan should come on.
Race Director
Joined: Apr 2002
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From: Anaheim CA
The main fan behind the radiator is controlled by the ECM. It uses the CTS (Coolant Temperature Sensor) on the front of the intake manifold to determine when to turn on the fan. The turn on point is set in the programming and is usually 228°.
The ECM uses the coolant cycling switch on the high pressure HVAC line to tell the ECM that the AC compressor is running. If the fan runs when that switch is jumpered then the entire chain of fan control components is working.
On my car the auxiliary fan temperature switch closes at 238°. I believe that temperature is standard on all C4s and also applies to the later cars that have ECM controlled secondary fans.
The ECM uses the coolant cycling switch on the high pressure HVAC line to tell the ECM that the AC compressor is running. If the fan runs when that switch is jumpered then the entire chain of fan control components is working.
On my car the auxiliary fan temperature switch closes at 238°. I believe that temperature is standard on all C4s and also applies to the later cars that have ECM controlled secondary fans.
Le Mans Master
Joined: Jul 2004
Posts: 6,228
Likes: 698
From: Clifton Park, NY ............Clearwater, FL ... 85 Original Owner
Hello, My car runs pretty hot, as do what seems like all the l-98s. Well my rad boost fan will kick on when it gets too hot around 228 but my main fan, that runs with the ac, does not. I know the fan motor works because I jumped the ac pressure sensor switch and it came on... but it doesn't seem to run when the car needs to be cooled. I am guessing its the relay, but what else could cause this? and is there a temp sensor I can replace to get my main fan to come on at a lower than spec rating? I HATE that this car runs so hot, it stresses me out. Thanks guys always appreciate the help! Also is there a way to jumper that relay to test? thanks! I hate throwing money at the car without knowing what I need!
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
Thread Starter
Racer
Joined: Sep 2014
Posts: 421
Likes: 34
From: Troy Michigan
The main fan behind the radiator is controlled by the ECM. It uses the CTS (Coolant Temperature Sensor) on the front of the intake manifold to determine when to turn on the fan. The turn on point is set in the programming and is usually 228°.
The ECM uses the coolant cycling switch on the high pressure HVAC line to tell the ECM that the AC compressor is running. If the fan runs when that switch is jumpered then the entire chain of fan control components is working.
On my car the auxiliary fan temperature switch closes at 238°. I believe that temperature is standard on all C4s and also applies to the later cars that have ECM controlled secondary fans.
The ECM uses the coolant cycling switch on the high pressure HVAC line to tell the ECM that the AC compressor is running. If the fan runs when that switch is jumpered then the entire chain of fan control components is working.
On my car the auxiliary fan temperature switch closes at 238°. I believe that temperature is standard on all C4s and also applies to the later cars that have ECM controlled secondary fans.
Le Mans Master
Joined: Jul 2004
Posts: 6,228
Likes: 698
From: Clifton Park, NY ............Clearwater, FL ... 85 Original Owner
Thank you this is very helpful. So the fan and relay work which is great. Its strange tho, I sat down with the car yesterday and allowed it to warm up, The aux rad boost fan kicked in at about 218, so it came on according to this very early. The car got up around mid 220's it did hit 228 isn't overheating. But the primary A/C Fan didn't come on. Is it possible to have the fan come on at about 225? that's about as hot as it want it too get
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Race Director
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From: Overland Park Kansas
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If the computer isn't "seeing" the correct temperature, other issues could be occuring. Rich?
There's a reason the fan isn't coming on. I wouldn't want to go into next summer with that problem.
Team Owner
Joined: Sep 2003
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Thank you this is very helpful. So the fan and relay work which is great. Its strange tho, I sat down with the car yesterday and allowed it to warm up, The aux rad boost fan kicked in at about 218, so it came on according to this very early. The car got up around mid 220's it did hit 228 isn't overheating. But the primary A/C Fan didn't come on. Is it possible to have the fan come on at about 225? that's about as hot as it want it too get
The switch that controls the AUX could very well have been changed OR again you're using the TEMP GAUGE @ cluster to try and evaluate a component controlled by a different still device.
Your car has three TEMP SENDER/SWITCH/SENSOR components that aren't related.
CTS @ intake supplies ECM with values.
Sender in cylinder head supplies information to cluster.
Switch in other cylinder head turn on/off AUX fan.
If you're using a scanner and have mentioned the TEMPS seen by it then yes you have issues and I'm wrong in my assumptions.
You need to scan the car and compare the cluster temps displayed to those being seen by the ECM.
2nd Gear
Joined: Oct 2016
Posts: 2
Likes: 0
89 Main fan not running
I have the same problem. I checked the fan relay and the fan comes on when I ground the relay. So what would be the best way to check the sensor supplying the ECM. Do I just replace it with a new sensor? I know one thing. I need a total rewire, the last owner let water set in the rear and the back harness copper is all black from corrosion. And the engine compartment is suffering because the insulation on the exposed wires is getting very brittle.
You're trying to (it seems) to use the TEMP GAUGE @ the cluster to gauge the performance of your CTS/COOLING ETC> That doesn't work. The TEMP SENDER/SENSOR for the cluster isn't known to be anything more than an "approximation" of the coolant temp. The ECM uses the CTS for fan control. You could confirm the fan operation using a scanner to check CTS values seen by the ECM, if the ECM doesn't see the TEMP required from the CTS it isn't going to turn on. Could you have a bad CTS? Maybe You need to check the proper components to determine efficiency and "it seems" YOU'RE NOT!
The switch that controls the AUX could very well have been changed OR again you're using the TEMP GAUGE @ cluster to try and evaluate a component controlled by a different still device.
Your car has three TEMP SENDER/SWITCH/SENSOR components that aren't related.
CTS @ intake supplies ECM with values.
Sender in cylinder head supplies information to cluster.
Switch in other cylinder head turn on/off AUX fan.
If you're using a scanner and have mentioned the TEMPS seen by it then yes you have issues and I'm wrong in my assumptions.
You need to scan the car and compare the cluster temps displayed to those being seen by the ECM.
The switch that controls the AUX could very well have been changed OR again you're using the TEMP GAUGE @ cluster to try and evaluate a component controlled by a different still device.
Your car has three TEMP SENDER/SWITCH/SENSOR components that aren't related.
CTS @ intake supplies ECM with values.
Sender in cylinder head supplies information to cluster.
Switch in other cylinder head turn on/off AUX fan.
If you're using a scanner and have mentioned the TEMPS seen by it then yes you have issues and I'm wrong in my assumptions.
You need to scan the car and compare the cluster temps displayed to those being seen by the ECM.
Team Owner
Joined: Jul 2004
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From: Hartford WI
Team Owner
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http://pe-ltd.com/assets/coolant_temp.pdf
Here's values most commonly found and used for diagnostics in most random searches. If you've the correct FSM for your car the values are also there.
http://www.chevythunder.com/ecm_comp...onent_fun2.htm