Engine Fan self turning

I have a 1991 Honda Accord with 250, 000 miles on the odometer.

It has happened a couple times in the past 2 months when the engine fan turns itself on after the ignition has been turned off. The latest incident was a couple days ago when the fan repeatedly turned itself on and off. I discovered by turning on the ignition to the first click would stop this. Engine temperature gauge shows engine operating temperature to be well within normal limits.

Question: why is this happening?

There is a temperature sensor in the radiator that triggers the fan relay at a preset temperature. Maybe the sensor or the relay is acting up.

This could be “normal” for this car. When you turn off the motor for a few minutes the motor gets hotter because the coolant isn’t circulating. Some cars were wired to allow the electric cooling fans to run even with the key out of the car to cool motor. Since this freaked some owners out - cars now cut the power to the fans when the ignition is off.

I agree with UncleTurbo here. I shared a carport with a neighbor in Arizona with a 90’s Honda and the cooling fan cycled on and off during warm weather. I was curious and looked it up and discovered that vehicles will “percolate” after they are shut off. That means that the temperature of the engine will increase after it’s no longer running.

This is normal for that vintage Accord. My '88 Accord did it too.
The temperature threshold to turn on the fan is lower with the ignition key off than when on.
It’s done to lower the overall temps under the hood, not just the coolant.
These cars had very low hoods for aerodynamics and tight packaging in the engine compartment,
leaving little space for natural convection.

Right from page 25 of the Owners Manual:

“If the engine has been running, some engine components
may be hot enough to burn you.
Keep hands away from the radiator fan. The fan may start
automatically without warning and run for up to 15 minutes,
even after the engine is turned off.”

Don’t have the manual, get one here free:

Ok, but why is the fan doing it now? It has never done this before! Could it be because of its age? And, should I do something about it or leave it be? It has done this twice in two months.

If you are certain this just started, it’s probably the temp sensor which controls the radiator fan. Those go bad, and can fail either way, the fan runs when it isn’t supposed to, or it doesn’t run when it is supposed to. I’ve had to replace that part in my Corolla twice now.

The way I confirmed the diagnosis, I removed it and put it in a pot of water and heated it up on the stove with a thermometer and a ohm meter. It wasn’t turning on and off at the temperatures it was supposed to. And it was was intermittent, would work one cycle, but not the next. This is a fairly simple experiment to do if you are the mad-scientist type.

In the meantime, be aware that your fan switch is suspect which will cause you engine to overheat, esp when driving around town or idling. On the freeway the radiator fan usually doesn’t come on as there is sufficient airflow already. So keep an eye on the engine coolant temp gauge on the dashboard, esp when in a situation of long idles, like waiting at a drive through window, etc. You don’t want a small problem to become a big, expensive problem.

So the best thing to do is watch the engine coolant temperature gauge which registers normal engine operating temperature and have the radiator fan temp control sensor/fan switch changed. Are the fan temp control sensor and fan switch the same or not? Any idea as to the cost?

And, I find these screens to not be user friendly. :frowning:

I don’t think you have a problem. The weather is warmer so the vehicle is responding to it. If the fan keeps running and kills your battery…I would check into it further. Otherwise…the car is acting normal.

@Hondi - how long have you owned this car? I can’t really say why it is doing it now, but if the car is a recent acquisition it may just be something you get used to. The only real issue is when servicing the car with the hood up you must be aware the fan could come on and keep your hands, and tools clear of it. The fan might cycle on an off one or two times and then stay off. This should not be a problem and the battery won’t rundown if the fan only runs for 5 min. or so each cycle. In the '80’s and '90’s I remember walking in mall parking lots on a hot day and I’d hear several fans running on different cars as I walked along so it was very common back then. Now I don’t hear it anymore so car makers adjusted to customer preference.

“It has never done this before!”

Sometimes the fan on my '88 Accord would come on several minutes after shutting the engine off.
There’s a warning label about this somewhere under the hood.
Maybe you’ve just been walking away from the car after parking and not caught it “in the act”.
As long as it runs a couple of minutes and shuts off it’s OK.

I think Ive seen the type of fan running you are talking about on Hondas SPECIFICALLY… That is if you are describing the engine fan running at ANY TIME day or nite with the vehicle COLD. If this is your predicament let me know. If you had been recently running this Honda ANYTIME during the past say 4-5 hrs? Any Honda Fan play would STILL be fair game… Is it possible you have just become witness to the fan by accident and it has been doing this all its life… I know HOndas pretty well and they have a pretty BIG window in which they can run their cooling fans… Its only when you know the engine is COLD…and the fan is still cycling that you have a problem.

I’m talking about a Cold Honda with the fan cycling…if this describes you…let me know.

If you had been driving the vehicle within the past 4 hrs or so…Fan running is still fair game


OP writes …

Are the fan temp control sensor and fan switch the same or not?

Every car design is different. You’d have to look up how this function on yours works on your car in the factory service manual, assuming that nobody here knows already.

A little background info. On my Corolla the “radiator fan temperature switch” is an easily removable device, inexpensive, screwed into the coolant jacket, and is a simple single pole, single throw switch. It is on (low resistance) whenever the coolant is below 195 degrees, and off when the coolant goes over 195 degrees. That switch controls a relay, and the relay powers the radiator fan. One way I test this function, I disconnect the wiring harness at the switch with the engine coolant cold, and the radiator fan comes on. I think it is done that way as a fail-safe, if that connector were to fall off the fan would run all the time, which is better than it never running. On my Corolla – this is apparently different than your car – the radiator fan cannot come on unless the ignition key is in the “on” position. The radiator fan stops once I remove the key from the ignition no matter how hot the coolant is. I’m not sure that’s a good feature, it seems like it would better for the engine to keep the fan running awhile until the coolant reaches a lower temperature, but the hot coolant at engine shut-off situation doesn’t seem to have done any damage.

Edit: Just curious, what is it about the format of these forum pages that you don’t like?