Fan running after shutdown

It's normal. The fan is driven by a thermostat and runs to cool the engine down to the stat setting - even after the engine is switched off.

Most likely to do it if you stop fairly suddenly immediately after working the engine quite hard - or even after idling for a while with the car stationary.

Ok, thanks.

Does it mean anything that my car just recently started doing this? It happens every time I drive it, really, and never did before. Does this mean the engine isn't handling the work as well as it once did for some reason and therefore heating up more?

Ok, thanks.

Does it mean anything that my car just recently started doing this? It happens every time I drive it, really, and never did before. Does this mean the engine isn't handling the work as well as it once did for some reason and therefore heating up more?

Or that perhaps the thermostat system is a bit out of whack?

Could well be the thermostat.

Is there any evidence that the engine *is* running hotter? For example, is the temperature gauge nearer the red than usual? If not, it's probably nothing to worry about.

Try a thorough flush of the coolant system and replacing the coolant (50% antifreeze) and while you are at it check the thermostat for correct operation.

Cheers, Peter.

It definitely means something. Something has changed, and my vote says it's the thermostat. Mine did the exact same thing. ('96 850T) I took it to the dealer for this one. It was only like $90 repair apprently thermostats are cheap. At any rate it is worth noting that while I did notice the fan running first, my temp gauge was a little north of usual. But never into the extreme range.... just a little hotter than normal.

FYI

Has the weather gotten warmer where you are?

Gary

Ah, you might be onto something there, Gary. You're thinking out of the box. It has been warming up, and that could well be contributing.

In terms of checking the thermostat to be sure it's operating correctly... how exactly would you recommend doing that? And, um, where is it!?

-Larry

Well, I wasn't sure if you were north or south of the equator; if north, the fan activity is probably normal, if south, it's likely indicating a problem.

There should be a hose about 2.5" in diameter running from the top of the radiator at one corner to the top of the engine at the front. There'll be a small housing that the hose attaches to; the housing is usually mounted to the engine with two bolts. This little housing contains the thermostat.

A simple way to test is with the engine cold; make sure the coolant is topped up, then start the engine. Every 20-30 seconds, feel the radiator hose. It'll stay at ambient temperature for a few minutes, then suddenly get a lot warmer if the thermostat is working right.

If it never gets significantly warmer, the thermostat is stuck closed.

If it gets warmer gradually over the first few minutes and doesn't have the sudden increase, the thermostat is stuck open.

There are specified temperatures at which a thermostat should open or close, but generally, they either work right or not at all.

Gary

There are two entirely separate thermostats which may have an influence.

First, there is the engine thermostat. This is a purely mechanical device in which a disc - operated by a wax capsule - covers a hole and stops the engine water from flowing through the radiator. At a certain temperature, the wax expands and moves the disc out of the hole - allowing water to flow through the radiator. If this fails, or loses some of its wax, it will not open fully - or at all - and the engine will get hotter than normal - maybe dangerously so.

Then there's the fan thermostat - which is electrical or electronic. This is driven by a sensor which measures engine temperature, and the 'stat' switches the fan on above a certain temperature. [It's distinctly possible that the logic for this operation is implemented in one of the on-board computers these days - rather than being a thermostat per se].

So if the fan runs more often than usual, it could be because the engine

*is* hotter - possibly as the result of a problem with the engine thermostat - or it could simply mean that the fan stat (however that is implemented) *thinks* that the engine is hotter - possibly as the result of a faulty sensor.

Expanding on this... On the later Bosch injected 940s (of which this is one), all 960s, 850s and later, the ECU does determine when the fan comes on based on temperature from the coolant temperature sensor. The computer always assumes the thermostat is working correctly and that there is a problem with the coolant temperature sensor if the engine doesn't come up to the proper temperature at the proper speed. So it runs the fan all the time, assuming potential overheating. 99% of the time a new thermostat will fix this problem.