Overheating, Problem with Fans

[ally406]

I've noticed that on hot days in slow moving traffic the coolant temperature has sometimes reached the high 90's with no sign of the fans kicking in. When I had the car in at an air con place, their equipment displayed the temperature of the air con system and the fans clicked on and off exactly where they were meant to, so the fans work. I can hear them running when the air con is on. However, they don't seem to come on when when the coolant temperature is getting too high. One time in slow moving traffic I had to wind down the windows and stick the blower on full to keep the temperature down. I think just a faulty sensor or relay. Can anyone suggest where to start?

[jonsowman]

So I had a similar problem, which was compounded by the fact that I've got a slow coolant leak, and when coolant temp went over 90, the car would dump a lot of coolant! I changed the coolant and Bitron sensors but to no effect. I just came to the conclusion that the fan threshold temperature was marginally too high.

My solution (until I replace the rad and bottom hose, and maybe I'll even leave it there afterwards) was to wire a 10K potentiometer in series with the Bitron sensor in the engine bay. The potentiometer is mounted on a spare blanking plate in the centre console, and means I can now precisely set the fan threshold. I've got it set such that the moment the needle hits 90C, the fans come on.

The Bitron sensor is only for the fans, so my pot doesn't affect the temperature gauge or the ECU functions. It just affects the fans independently of everything else.

You could try this to see if it solves your problem. I hope that's of some help...

[poddack]

There are 3 coolant temperature sensors, one for the engine ECU, one for the dash and one for the fans/aircon.
So if the temperature is reading right one of the others may be dicky!

[ally406]

Thanks guys.

Would these sensors be located around the fuel filter housing? That area dos get very greasy, fingers crossed just cleaning up connectors with some WD40 will do the trick.

[jonsowman]

The fans/aircon one (Bitron) is on the fuel filter housing (brown connector), as is the one with the green connector (which I think is the ECU sensor). If that's right, I don't know where the dash temp sensor is located, sorry, maybe poddack can tell you

[ally406]

Thanks mate, there is a third one located behind the filter housing, which I therefor presume is the instrument panel readout. I'm confused about the aircon one. Why would the air con require a coolant sensor?

Anyways, I cleaned all the plugs and no difference. If I were to replace a sensor, I'm guessing the ECU one is my best bet? Reading around, I understand that the fan relays are located behind the bumper. I might try swapping them around to see if there's a faulty relay.

[jonsowman]

The Bitron (brown) sensor connects to the Bitron control unit, which is responsible for the cooling fans and the a/c system as I understand it. That's why that sensor is being called the "fans/aircon" sensor. So if that's faulty it could be the reason the cooling fans aren't coming on. Yep the one behind the fuel filter housing is probably the dash sensor then -- that'd make sense.

You're right, it could be the relay. If you just unplug the Bitron sensor (effectively making an infinite resistance) you should find the fans power up (give them a few seconds). If they don't, it's likely the relays or fans motors are suspect. If they do come on, then it's probably the sensor.

Let me know what happens

[ally406]

Thank you sir, weather depending, I will check that out over the week end

[poddack]

ditto

[Gary406]

i think another cause for fans not kicking in could be the relays .

3 green relays located on the front of the fan housing, (front grill needs to be removed to get to them)

£5 ish each from dealers.