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1998 Cavalier Radiator Fan Problem

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Apr 12, 2005, 1:24 PM

Post #1 of 4 (12697 views)
1998 Cavalier Radiator Fan Problem Sign In

I have a 1998 Chevy Cavalier and the radiator fan does not turn on when the engine heats up. The fan comes on when I turn on the A/C or defroster, but not when the engine heats up. The motor is fine and the relays seem to be functioning ok. I checked a coolant temp sensor on the line coming out of the coolant resevoir and it seems fine. When I disconnected the sensor, the gauge inside the car bottomed out and the engine idled fast trying to warm itself up. When I reconnected the sensor, the engine immediately adjusted the idle, but the fan did not come on. Is there another sensor to turn on the fan and if so, where is it located? Also, if anyone has any other ideas, I'd appreciate any and all information. It's starting to warm up and I want to get this taken care of ASAP. Thanks.

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DanD profile image

Apr 12, 2005, 5:49 PM

Post #2 of 4 (12683 views)
Re: 1998 Cavalier Radiator Fan Problem [In reply to] Sign In

I just went through the operating description for the cooling fan and checked a wiring diagram for the system.
The PCM has full control of the fan whether there is a request from the AC being turned on or if the coolant temp sensor reaches its threshold for the PCM to ground the relay to turn on the fan.
So if the PCM can turn on the fan when there is an AC request, we know that the one and only relay and the wiring from the computer must be ok.
You say that the temp sensor when disconnected makes the engine change RPM and that the gauge drops so it’s likely ok as well. Can’t be sure of that unless you scan the PCM's data list to see what the sensor is telling the PCM. There is only one sensor for coolant temps the one in the reservoir is a low coolant sensor.
Are you sure that you are waiting long enough for the engine too warm up to turn on the fan, because the PCM will not authorize the fan until the engine gets to 223 degrees, you know a watched pot never boils.
The next thing to think about is there a mechanical reason for this to happen, if the cooling system is low for whatever reason or if air is being introduced into the system and the sensor is not completely submerged in coolant it will not read properly. Air will no transfer the heat the same way as the liquid would.
Just a few thoughts on what maybe going on, lets keep talking and we’ll figure this out, just be careful not to overheat the engine until we do.

Canadian "EH"

New User

Apr 12, 2005, 8:37 PM

Post #3 of 4 (12678 views)
Re: 1998 Cavalier Radiator Fan Problem [In reply to] Sign In

I know the sensor at the bottom of the resevoir is the low coolant sensor. The sensor I checked is on the line coming from the resevoir. This is the sensor that made the RPM increase when it was disconnected. I see two sensors on the back of the engine block next to the oil filter. I thought one was for oil temp or pressure and the other may be another coolant temp sensor. Is this a possibility, or is there only one sensor on the 98 cavalier? The reason I think the fan isn't turning on now is that before I noticed the temp increasing, it never rose above 180 degrees unless the A/C was on and I was stopped in traffic. We definitely need to keep talking. Thanks.

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DanD profile image

Apr 13, 2005, 7:37 AM

Post #4 of 4 (12666 views)
Re: 1998 Cavalier Radiator Fan Problem [In reply to] Sign In

There is only the one coolant sensor on this car, the two you see at the back by the oil filter are the oil pressure switch and possibly the crank sensor or knock sensor.
It’s nothing to see the temp gauge go as high as ¾ before the fan will cycle.
What you could try is let the car run with the hood open and a garden hose ready. Keep a close watch on the gauge and if the fan doesn’t come on before it hits the red line hose down the rad with cold water, you wont hurt anything as long as you don’t allow it to overheat.
Best would be to have a scanner connected to watch data and see if the sensor is sending the proper information, or that the PCM is capable of interpreting it.

Canadian "EH"

1998 Cavalier Radiator Fan Problem

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