Radiator fan on when not needed.

[TXracefan1320]

I searched the forum but my problem seems a little different. After driving about 20 miles at highway speed without the A/C having been on once and the coolant temperature normal, the radiator fans come on and stay on. The coolant temp will go down to about 1/3 (normal is exactly 1/2 way up) but the fans stay on.
With the ignition off, they stop and stay off after restarting.

I have replaced the relay and swapped in my spare PCM but it still happens. Any ideas?

[RIP]

With the A/C is off the Engine Coolant Temp (ECT) sensor determines when the fans turn on and off. I would look in that direction. Test it and closely inspect the wiring and connections. BTW - You are one lucky man to have a spare PCM to try.

Which model year and engine?

[TXracefan1320]

I have a lot of spare parts for this POS but like others have said, when they are not messed up they are great vehicles.

What has me stumped is that after the fan has been on a while the coolant temp drops. The needle is below normal and the radiator hose is not as hot and not under as much pressure. So I think the temp sensor is working.

It's a 97 Grand Caravan with the 3.8 no AWD

[RIP]

Ok now I'm stumped. Easy to test the ECT though. If you like you can check operating temperatures using these figures. I would imagine some scanners are capable of monitoring engine temp.

"The fan operates based on temperature and A/C pressure.
On at 220deg F 30% speed, 230 Deg speed ramps up to 100%. Fan ramps back down from 100% to 31% and shuts off at 214Deg.

When AC is on, 30% speed at 250psi, ramps up with pressure to 99%, 300 PSI
ramps back down with pressure and turns off at 248 psi."

[TXracefan1320]

Any idea what the sensor resistance is at these temps? The service manual is pretty vague, it says "around 200F approx 700 to 1000 ohms." If I had more precise specs I could tell if the sensor was out of whack. I measured it at normal temp and got around 850.

Strange thing is, I can drive around town all day and if it's not too hot the fan will never come on. But if I hit the highway, after 20-30 mins, the fan is on even though the temp gauge is still normal.

[RIP]

Is this effecting anything besides you hearing the fans come on and staring at the temp gauge? Is it driving normally meaning no hesitation or stumbling, normal acceleration, shifting etc. Normal warm up and idle? Has it overheated? Has your mileage taken a hit? If the answer to these is no, then why are you concerned?

On my 96 the only time I can tell if the fans are coming on or not is at idle at a stop, otherwise, I have no idea. Even then it's not easy. Are you hearing the fans at speed on the highway? Another thing is these are variable speed fans. They aren't either on or off. The speed depends on the temp.

I've seen the resistance readings somewhere. I'll have to poke around the net.

[TXracefan1320]

It does not affect anything else on the vehicle.

The reason I am concerned is that this will cause the fans to wear out sooner. (I've replaced everything else, what's it matter?)