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2001 Nissan Altima Cooling Fan not cycling off

Hi Everyone
I have a 2001 Nissan Altima. I seem to be having a fan problem. I started noticing that about 2 seconds after I turned the car off, the fans would come back on and run for ~25-30 seconds. I brought it in and my mechanic was thinking maybe a defective thermostat, so we replaced that. It still keeps happening, but now I’ve realized that the fans come back on anytime the car is turned off when the fans are running. If the fans are not running, they won’t come back on. I’ve been trying to pay more attention to what is going on and when I first turn on the car, no fans are on (at least not the high fan, not sure if there are more than 1) After driving around town, the fans will turn on. Normally, I believe the fan should then turn off once the coolant temp gets below a certain level. I let the car sit idling in the driveway for 15 min and the fans never turned off. I took it back to mechanic and repeated the idling for 15 min, fans never turned off. He checked the coolant temp with some sort of sensor and the temps were reading between 166-170 depending on where he aimed his device, so he said the fans should be turning off and it doesn’t seem like the car is overheating.
If he unplugged the temperature sensor, the gauge would go all the way to cold, but nothing changed for the fans, so he didn’t think that was the problem.
He took the fan relays along the edge of the car and swapped them around and nothing changed, so didn’t think it was a relay problem
He removed some sensor on the passenger side on the back part of the engine and the fans got really loud and really fast. When he replace that, the fans would go back to normal until the engine temp got hot enough to turn them on and then they wouldn’t go off again. He’s thinking that sensor might be the problem, but isn’t 100% sure. I think he said this was the cooling fan sensor or switch.

On a side note that may or may not be related. About 5 years ago the water pump broke. It started having the fans on all the time (even from a cold start), that turned out to be a faulty knock sensor. There was a knock sensor code and he replaced the knock sensor and then the fans went back to normal cycling. I didn’t have any problems until early last fall, when I started noticing my current problems. I didn’t worry about it until now, because as it got colder outside, it wasn’t an issue. So outside temperature definitely effects it.

There are no codes this time.

Thanks
Jennifer

I don’t think you have a problem with your cooling fans. Cooling fans will turn on even if the engine is off in most vehicles. This is due to engine percolation. That means that your engine will actually heat up when the engine is off. As long as the fan(s) go off after a little while and you have no overheating problems then I think you are okay.

The car never did this in the many years that I’ve owned it until recently-with the exception of the knock sensor problem
Also, shouldn’t the fans cycle on and off when sitting? I seemed to recall sitting at drive thru windows (somewhere with a wall close) and hearing the fans kick on and off every few minutes.

Have you ever flushed the cooling system and replaced it with fresh coolant? The radiator may not be keeping the engine cool enough to cycle the cooling fans on and off. That’s the only scenario that I can come up with since it looks like your mechanic has pretty well covered all the bases.

No, we haven’t done the cooling system lately. Wouldn’t that have shown up when he took the various temperature readings. He took it from a bunch of different hoses. He seemed to think the temperature readings were low enough to have the fans be off. Definitely didn’t think it was an overheating problem

Is it possible it is the cooling fan sensor/switch (not the temp sensor but one for the fan?) like he is thinking or doesn’t that make sense?

The cooling fan sensor is a possibility but remember that the sensor is working normally in some aspects. I just don’t think that the proper parameters are being met (engine not cooled down enough) to turn off the cooling fans. As a vehicle ages many components like the radiator simply don’t work a well as when they were newer.

Thanks for all of your help. I don’t mean to question you, it’s just that this came on all of a sudden. One day it didn’t do it, the next it started doing it predictably. Even now, under 30’ it just doesn’t do it, because the fans don’t come on. Also, running defrost with high heat doesn’t help-which I’d always been taught to do with a overheating car. I guess I would have thought that if it is just the car getting older I would have noticed it more gradually. But, live and learn I guess.
So, is there anything I can do? If its doing this when it’s only 50’ outside I’m concerned about when it gets to 95!
I checked my records and had cooling system flushed at 95k, I’m now at 115k. Most if my driving is highway miles, very little stop and go. Interestingly; if I come from a cold engine down a big hill at 55mph, it won’t do it at the bottom, unless I’d been driving around at the top of the hill and the fans came on up there. The hill I’m talking about is about 7 miles long with a speed limit of 55. I live in the mountains. Shouldn’t the fans turn off at highway speeds?
Basically, is there anything I can do or am I looking at a car most likely overheating this summer?

I would check the price of the cooling fan sensor and if it’s not too expensive I would replace it for your piece of mind. I don’t usually replace parts on a whim but in this case I think it’s a good idea. Good luck.

thanks
if it is just the car is getting older and not cooling as well as it used to, is there anything I can to? Will this most likely lead to overheating in the summertime, or is it not really an issue?

You might want to have the cooling system flushed and new antifreeze (coolant) installed. Another thing you can do at no cost is to take a garden hose with a hose nozzle and from the inside of the radiator out through the front of the car. If you have access to an air hose, this works even better. I have done this with cars that have been running a little hotter than normal, and have flushed out all kinds of dead bugs and debris from the honeycomb of the radiator.