Engine 850: B5234T/2.3/20v/T5: engine wont start while fan is on

[amazondean]

That's great. Thanks, I will try it.

[Luxobarge]

I'm not convinced your fault has anything to do with the fan coming on or not. Earlier you said that sometimes (when it won't start) the temperature gauge shows cold even when the engine is hot. The temp gauge is driven from the same engine coolant temperature sensor as the one used for the engine management system (ECU) and therefore if the sensor is intermittently sending a cold engine signal to the ECU (and the temperature gauge) then I'm not surprised it won't start - it would be delivering a massively rich mixture into a hot engine, i.e. the ECU thinks it's starting a cold engine.

If it were me, I'd be concentrating my efforts around the engine coolant temp sensor, you can test whether it's working with a multimeter, I'm sure someone on here can give you typical resistance readings for both hot and cold, and if you're getting a "cold" reading when the engine is hot, that's your problem. If the readings are within the spec of the ECU, it won't throw a fault code, as the ECU simply thinks that the engine is a different temperature to what it actually is.

Just my thoughts, for what it's worth.

[amazondean]

Thanks for the responses so far

When the temperature needle is showing cold when it should be reading hot. (Middle) it will only do this once the car has reached its temperature and then the car is switched off, but only after the car has been switched off for a couple of minutes. If I switch the ignition off and then back on straight away the temperature needle moves to the middle, and the car will always start. If I wait about three minutes the needle will stay fixed to the bottom and will not start at all.

I have so far concluded that the only significance the fan has is that the engine has reached a temperature that then requires cooling. The fan will work as it should and come on and off with no problem while the engine is running, the temperature never falters. The car will always start again, as long as the fan hasn’t needed to come on.

The problem seems to be that once the fan is needed AND when I switch the car off and wait a couple of minutes, the needle then decides to drop to the bottom. It is as though the engines temperature is still climbing once the car is turned off and a safety mechanism is telling the car not to start as it is too hot. The temp needle is fixed to the bottom. If the needle moves to the middle it will always start.

. I feel that the temp sensor is doing its job, as the cars temperature is always correct while running and as long as the car isn’t getting over hot (the fan not being needed) will always start once the car has stopped.

A lot to take in, I hope I am explaining myself well enough for people to understand the problem.

Thanks.

[amazondean]

Just an update.

I found an earth just in front of the battery. I have removed, cleaned and reinstated. Since doing this, the car has always started, even when hot and the temp needle has always moved to the middle. I have not had it on the road yet but I have done my usual test several times and it has always started.

I am not convinced as yet that I have solved it as I can't believe it could be that simple. Thank you Laird Scooby for that suggestion. I am keeping my fingers crossed.

Today I have replaced the small gear in the instrument panel, my next job is to look at the PCV breather system and replace all that. Not straight forward by the sound of it. After that, the front top strut rubber bearings need replacing.