It’s been a classic British summer so far in 2016 – Fairly mild with the odd sunny day thrown in. This week however, it has been HOT! The perfect time to get the Roadster out of the garage and use it as my commuting car.
Ever since I’ve owned the car I’ve been confident in it’s reliability but I’ve never been driving in such hot weather as on Tuesday. During the 20 minute drive home the temperature gauge was higher than normal – Sitting at the 12 o’clock position and as I pulled on to the drive way it was well past. After opening the bonnet, the reason was clear, the cooling fan wasn’t on.
This weekend I set about trying to workout what the problem was. After a bit of research on the MX-5 owners club forum and MX5NUTZ it was clear there were three possible points of failure. The fan motor, the fan relay or the thermostat. Checking each of these components was really simple and any DIYer can do it.
How to check the cooling fan motor
Open the diagnostics box on the near side of the engine bay (Its a little black box).
Take a paper clip that you’ve straightened out and push one end in to the terminal marked as GND and TFA.
Turn on the car’s ignition and if the fan motor is working it should turn on.
How to test the relay
From the fuse box inside the engine bay on the offside, remove the smaller black relay marked LA10.
After setting my new multimeter up to check for continuity I attached the probes to the larger two of the four terminals.
In this state the multimeter should show OL or Open Loop, indicating there isn’t a circuit.
At this point I realised I needed a power source to trip the relay so headed off to Maplin for a 9v battery and connector. Once, connected touching the two wires from the battery to the other two terminals in the relay I heard a click and the multimeter beeped letting me know the relay was functioning fine.
Replace the relay back in the fuse box.
Testing the thermoswitch
To double check the relay I found a suggestion on how to test the thermoswitch, This is the connector that attaches to the thermostat on the front of the engine right in front of the rocker cover. Remove the connector from the thermostat gently and push the same paper clip as before in to it.
With the engine running touch the paper clip on to bare metal – I found the intake manifold and the rocker cover both worked. If the fan runs that you know that this switch and the relay are working fine.
Temperature sensor
With the thermoswitch, relay and fan motor all confirmed to be functioning the next item to test would be the temperature sensor. It’s possible to remove this item partially immerse the sensor in water and test for continuity at 91c. However I decided that this was most likely the part to have failed so ordered http://www.autolinkmx5.com/temperature-sensor-mazda-mx-5-16-mk1-fan-switch-front-of-engine-376-p.asp as a replacement.
Mk1 MX5 Eunos 