Mx5 Mk1 97 1.8 - Fan not kicking in! Pretty urgent!

Hi All,

My fan doesn’t seem to want to start. The engine is getting very hot! 


I fitted a new alloy rad in Jan

I have bypassed the fan it in the diagnostic port and it does work when I do that. 

I bought a new green temp sensor and replaced that under the coil pack. 

I have checked the loom and that seems ok

I have replaced the relay in the fuse box

I have swapped round the 30amp fuses to see if one of those was faulty.


The car is going to sit in traffic next week and I urgently need to get to the bottom of the issue. 

Anyone got any ideas what could be stopping it working? would appreciate any further pointers.










The sensor for the fan is on top of the thermostat at the front of the engine. If you have physically tested the fan and relay, this will likely be the problem.

The temperature sensor at the back of the engine does not turn the fan on with the 1.6 NA.


Hi the engine is a 1.8L





Yes I noticed that. I have a feeling you may not have got all the air out the system but that is a long shot.

Start engine from cold with some coolant in a large jug.

Heater at hot but not sure that makes a difference.

Stand there for say 15 minutes until the thermostat opens. Keep an eye on the radiator coolant level as it can drop very fast.

Can you confirm the thermostat is opening by feeling the radiator and top hose getting hot when the thermostat opens.

Take up the carpet in the passenger side and make sure water has not got to the ECU terminals and rust is giving a bad connection.

Wrong sensor you should have fitted the grey sensor. No idea what the differance is but that is a 1.6 sensor.


Get the carpet lifted to check for water damage.

Checked under carpet, dry there no ingress whilst I’ve had the car. The sensor is the correct one bought from MX5 heaven and correct part for the year just checked order and package.


OK, this sounds like is a non Mazda original replacement part. It would be the wrong part if it was a genuine Mazda replacement part.

Therefore apart from bleeding the system again, you could wire in a switch until you find the problem.

Thanks! I re-bled the system tnite and there was an airlock!!! Raised it up on the ramps, heater full blast and squeezed the rad pipe until no more bubbles. I thought I had done it properly the first time but I hadn’t. Thanks all!!!

Even though i didn’t contribute to this thread, it is really appreciated when somebody reports back and says ‘thanks’!

Hi Mooks

Sorry I replied quickly and misread the engine size,

Someone came round at 5.00pm to pick up an ECU kit and just been chatting for five hours solid.

Very pleased to hear you have sorted this out.  

Great you got it sorted!