merchauser

first off, I don't have any cooling issues and my fans work great. radiator,
thermostat, hoses, fans, and cooling system are all good.

after a drive, prior to shut down, my fans are on. shut the car down
and the fans go out. but, if I turn the key to the on position, (car not running)
the fans will come back on.

this suggests to me that a water temp sensor wants the fans to run until
water temp is lowered. seems to me that should also work with key off?

is this correct?

the sensor at the rear of the intake will also triggerthe fans to run after shut down,
but that is dependent on intake air temp. on very hot days the fans will run after shut
down getting their cue from this sensor.

is that intake sensor the only one that will make the fans run on after shut
down, or should the water temp sensors(s) perform the same way?

Bertrand Daoust

Two things come to mind.

- There's a temperature sensor related to the transmission. On auto. at least, not sure on 5 speed. If it's above a certain temperature, the fan will stay on until the temperature gets down. EDIT: Not applicable to 5 speed, auto. only. Edit 2: This (fans on) applies with the key to the "off" position or removed from the ignition switch. So not your case here.

- If your heating/cooling system is in the re-circulation mode, the fans will stay on above, if I remember well, 0 degree C. The system puts the AC on when in re-circulation.

545svk

Hi, watching with interest as my '87 auto does the same.

dr bob

The switch on the transmission is in the fitting for the cooler line, forward left on the transmission. The switch setting shows 110 C as the close point. Researching similar switches I see 10 degree dead and is common.

Keeps the fans running until convection moves heat forward and out of the gearbox.

There are some options for combo switch/gauge senders there too

merchauser

dr. bob, good information to note for auto cars, but my car is a 5 speed.

545svk reports the same issue as mine; its that the standard operating procedure??

dr bob

Your fans are working as designed.

Ad0911

To my limited knowledge the fan is switched on/off by thermoswitch in the radiator. The key switch is not in this circuit. So it has a mind of its own.

worf928

Remember that the fans are supposed to run if the A/C compressor is enganged. If the A/C button is pushed-in (and the A/C system is functioning properly) the fans will operate as soon as the key is turned.

merchauser

yes, the fans work properly with the AC

beginning to understand and system would be working as it should

but logic tells me, that if the thermo switch "tells" the fans that the temperature is at a certain threshold,
then the fans should stay on regardless of ignition switch just like the intake sensor, until that temp is lowered.

Alan

No - you are overthinking things. It seems every thing is working fine.

The fan after-running is not something you want to do routinely (it's a huge battery load) - so it is limited to times when the engine is very hot. In many climates it may never get this hot.

In Phoenix in summer time it can be a common event - But! usually only when you run at high speed for a while then relatively quickly come to a stop and shutdown. This high load situation then relatively quick loss of coolant circulation is the most common trigger I see - and of course it is best avoided when possible.

Note that it is only indirectly related to air temp - its not the ambient air that directly triggers the intake switch its the heat from the engine underneath it. But when the ambient temp is very high the residual heat from a hot engine has a much harder time dissipating as quickly.

That the coolant is hot enough to need the cooling fans running IF the engine were running - does not mean it also needs the fan running without the engine running - these are quite different cases.

Given that after shutdown the coolant isn't circulating (hardly at all) - the radiator cooling fans will cool the radiator quickly without that having much effect on the engine - it's likely the airflow around the engine/exhaust that provides the most engine cooling effect. All that is needed is to reduce the risk of the heads getting too hot, and possibly also to assist in cooling the cats down (for other reasons).

Alan

Ducman82

sounds like it is working fine.

merchauser

agreed! everything is as is should be.

You are correct Alan, and thank you for the logical explanation; it makes sense to me now. time to move on to another issue.