MX-5 OC Forum

Once up to normal running temperature my cooling fan cuts in but then seems to run most of the time. I put a new radiator/cap/thermostat in a while ago to cure a slight running hot problem and all is fine. Now the temp gauge reads normal ie just below mid way.

Now is this normal for the fan to run most of the time or do I need to replace the fan sensor.

Can anyone confirm, but I think the cooling fan sensor is the one in the top of the thermostat housing. I can only assume it is getting a bit slow to react to when the fan has cooled things down. Also does this sensor control the temp gauge, as that is reading normal or is there a seperate one for that.

Hi Ya

 The fan should not run most of the time, mine runs only if sitting in traffic for 20 mins or so

 you're right that the sensor is on top of the Thermostat housing.

 On your R ltd you have 2 fans , The one one the left (as you look at the engine bay) is for the A/C the right one is the cooling fan

 I would also check the coolant level and for a blocked radiator , and insure a OE rad cap is fitted

 Hope this helps

Fergy

Martin,

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Fergyuk:

Martin,

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 Try now.

The gauge sensor is different to the fan switch. The gauge sensor is hidden on the back of the cylinder head below the crank angle sensor with a single spade terminal on it.

As Fergyuk said, the cause of the long running fan may be restricted coolant flow in the rad but something to bare in mind is it may also be caused by restricted airflow through the radiator.

I've known NB's to have this issue & I've yet find the cause. The fan just runs & runs once the engine is up to temperaure and just hold the engine temp stable, it doesn't increase or decrease. I find that if I just lift the revs up to a fast idle of around 1500rpm, this seems to circulate the coolant that little bit more and the engine temp drops and the fan stops. I think NB's just have a very low flowing cooling system.

Ok guys, thanks for the replies, so it could be a bit normal. I know the rad is fine as it is new , as is the genuine cap and thermostat. I may try a new sensor to see if it changes anything. As I say the temp runs normal so it is not a big issue. Maybe on cars fitted with air con the air con rad restricts a bit of air flow to the cooling rad.

Phil H:

Ok guys, thanks for the replies, so it could be a bit normal.

Be aware I have only ever come across this phenomenon on an NB & never on an NA.

 Hmm on my mk1 the fan hardly ever comes on, only when sitting in very heavy traffic. I've started the car at home many times when doing things and never actually seen it turn on when just ticking over from cold!

 It'd be nice it if came on more often, just to reassure me it's still working!

 Mine is also a cruddy old rad too, you can't really see through it anymore from the front, but inside is still nice and clean!