Lectric cooling fans....

mommucked

mommucked

Endeavoring to persevere
Joined
Sep 26, 2011
Location
Rural Apex n.c.
The 2 on the 03 3.4 v6 Toyota Highlander run fine when the engine and AC are on........can't seem to see or hear them running at all when motor idles and the AC is turned off even after driving 30+ mins. on a 90's afternoon....turn off the AC and both fans stop . The temp gauge seems to wonder up and down a bit from normal this summer, though it never gets near the red zone. Could the temp sensor need replacing ?
 
The fans are supposed to be running with the AC on at idle; that behavior is triggered by the ECU. The fans won't both kick on when the AC is off unless the engine is way too hot. Often the two fans are controlled independently, and sometimes have two speeds, so you may not hear a single fan cycle on and off at idle but will obviously hear them both at full blast. The fan behavior sounds fine.

If the temp gauge is wandering around when you're driving, I wouldn't suspect the fans because they generally don't run when there's enough airflow, etc.. The temp sender (for the gauge) may be the suspect, not the temp sensor for the ECU (and fan control) unless the engine temp climbs too high at idle or in traffic and wants to overheat. I'm assuming your engine has both sensors because it's old enough to make that still very common.

You may also have a thermostat that is starting to stick or not fully actuate. Does it have an OEM or an aftermarket thermostat in it?
 
I had a Saturn that behaved like this. One fan, but it had two control circuits and relays. In normal driving, the fan would never kick on and Temps could get scary in slow traffic. Turn on the AC and all was well. I chased the temp sensor, replaced the ecm, did everything I could. Then I started playing with the relay. I could grab and twist the relay and the fan would kick on. The socket on the power side of the relay was weak. I bent a curve into the relay leg, reinstalled it, and never saw the problem again.
 
Fabrik8 said:
The fans are supposed to be running with the AC on at idle; that behavior is triggered by the ECU. The fans won't both kick on when the AC is off unless the engine is way too hot. Often the two fans are controlled independently, and sometimes have two speeds, so you may not hear a single fan cycle on and off at idle but will obviously hear them both at full blast. The fan behavior sounds fine.

If the temp gauge is wandering around when you're driving, I wouldn't suspect the fans because they generally don't run when there's enough airflow, etc.. The temp sender (for the gauge) may be the suspect, not the temp sensor for the ECU (and fan control) unless the engine temp climbs too high at idle or in traffic and wants to overheat. I'm assuming your engine has both sensors because it's old enough to make that still very common.

You may also have a thermostat that is starting to stick or not fully actuate. Does it have an OEM or an aftermarket thermostat in it?
Click to expand...

The dealership replaced the timing belt at the schd. time, almost 30k ago and I assume the wp and thermostat etc. were too ? the car runs well but it does seem to lose a bit of power when it's hot, regardless of the AC being on or off.
 
mommucked said:
The dealership replaced the timing belt at the schd. time, almost 30k ago and I assume the wp and thermostat etc. were too ? the car runs well but it does seem to lose a bit of power when it's hot, regardless of the AC being on or off.
Click to expand...

Thermostat replacement may be a bad assumption, and new thermostats do go bad as well. I've seen enough that I always test new ones before installing. (and I'm not even a pro mechanic who changes a lot of thermostats).

If you're losing more power than you normally do when hot, that could be a sign of a faulty temp sensor though, as that is directly connected to fuel and spark compensation from the ECU. And if that's the same sensor that the ECU uses for fan control, then........

You can test that sensor with a multimeter and see what that tells you. They just change resistance with temperature, so they're generally easy to remove and test in a pot of water with a thermometer and a multimeter if you can find out what the resistance should be at a few discrete points.
 
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