I’m currently diagnosing a cooling issue with my 5. The fan doesn’t come on and the car is overheating. I’ve checked the fan’s motor and that’s fine, the LA10 relay seems OK too. I’ve also changed the coolant and thermostat.
The last thing is the thermoswitch which I read could be the issue. On every photo I’ve seen the thermoswitch is on top of the thermostat, however on mine it isn’t. Any ideas where it might be?
Look at the rear of the engine by the water elbow. There is one for the ECU and one for the dash display. I don’t know about your car because my MK1 engined car uses the aftermarket ECU to control the fan, but most cars have a sender in the bottom of the radiator that switches the cooling fan.
Have you tried ‘burping’ the coolant system?
Try parking the car nose up hill (or small ramps) leave the rad cap off and internal heater set to full, then run the engine with the heater blower at full blast for a good ten minuets or so.
It might just be an air lock in the system.
It’s worth a try.
Thanks for the advice!
When I’m driving, I’ll have to turn the heaters on full blast and the temp needle will go straight back to normal. Do you think this is something to do with air being in the system?
Thanks! I’ll have a look
Have you checked the engine rad is getting hot? The stat could be stuck shut.
There is a small hose from the top of the water pump to the thermostat housing for self bleeding (visible in your photo), that should get most of the air out. You have to be sure the jiggle pin in the stat is at 12 o’clock too, it’s purpose is to allow a very restricted volume flow thru the stat so that some water flow is always active, without this flow the stat would be in static water from cold so would never see the water temperature and thus be unable to open. This would cause overheating too.
I’m not aware of any problems with this engine in regards to air locks, you ‘can’ alter the flow path for more even cooling but on a standard car it’s very much overkill. As for air locks, I’ve never had one with stock cooling. I just drop the coolant and refill, fire her up for a minute, top up and stick the rad cap on. Job done.
Thanks for the advice, the rad cap is extremely hot and the coolant overflow is boiling over, with excess coolant/water dripping out when hot.
As for the thermostat, I recently changed it but didn’t check which way the jiggle pin was so it could be that (I didn’t think it would be an issue).
P.s The engine is completely stock and it was running find for the first 2 years of ownership, just recently its been happening
Jiggle pin not at top can cause an air lock yes.
Based on that description, I’d suspect a blocked radiator.
The cooling fan on your car is controlled by the engine ECU. There is a terminal in the diagnostic socket under the bonnet called TFA, Test Fan, if you ground that with the ignition on does the fan run?
Ah yes I’ve heard about this. I tried it with a paperclip and the fan was running fine, maybe a new radiator is in order?
Does your rad leak or have all of its fins missing then? If it is in good condition I’d be reluctant to change it. Remove it and check it over. See that it’s not full of crud but if it is so is your engine, that’s another problem.
First thing I’d do is check your fan runs. Then remove the stat and check it opens in a boiling pan of water, it should open before boiling actually, if you have a thermometer check when it opens. If that’s ok refit with jiggle
Pin at top. The …
I’ve had someone look at the rad and they’ve said it’s fine, and visually there’s no fins missing. The only thing I’ve noticed if that when I top it up, the water is orange in colour (rusty).
The thermostat is brand new and should work fine, the old thermostat was fine too apart from being rusty. So I don’t think the stat is the issue.
I’ve heard rads are easy to fit so it might be worth changing it all out and seeing if that solves the issue. Thanks for the help!
You say in your first post the fan is not coming on, surely this must be the problem. I seem to remember there are two sensors, one for the ecu and one for the gauge.
Put a link in the diagnostic port and see if the fan comes on, if it does leave the engine running and see if it overheats. If the fan doesn’t come on diagnose why. If the engine doesn’t overheat with the fan running my guess would be the temperature sensor for the ecu.
Also have you checked for damp around the ecu and its connections. This has been known to cause all sorts of problems.
Is you car a 1.6 or 1.8? Not sure if that makes a difference to the sensor location. Mine is a 1.8, I’ll try and take a look at it later.
Good luck.
D
Mine is a 1.8 too.
I’ve tried the method of connecting the fan to the ignition in the diagnostics port and the fan runs fine when the ignition is on. I’ll have a look for the ECU this morning and check for damp, if it is just the temperature sensor, is it a case of buying a new ECU all together? And how easy are these to fit?
Okay, I’ve just been out and looked at mine.
The manual says the sensor for the ECU is under the coil pack ( the sensor for the gauge is on the side of the heater outlet casting below and to the side of the ECU sensor I think but not sure on this ). I’ve looked from every angle and used a small mirror but for the life of me I can’t see either of them. I think your next move is to remove the coil pack and check the connection of the sensor. Removing the coil pack can be a real pain unless the bracket has been modified so the bottom bolt dosn’t have to be removed, but that’s another story. If the connection looks okay you can remove the sensor and test it but to be honest if you’re going to the effort of removing it to test it you may as well fit a new sensor. To test it you have to put it in water and heat it up while measuring the resistance. MX5parts sell them and are 10% off today.
https://www.mx5parts.co.uk/sensor-water-temperature-rear-genuine-mazda-mk1-p-703.html
They also do an aftermarket one that is cheaper.
To remove it you have to drain about half the coolant, then it unscrews.
Good luck and let us know how you get on.
D
Brilliant thanks for the help! I’ll have a look today and play around with the coil pack and sensor.
Hi again, so an update with the overheating issue. The fan is working fine! I drove through the peak district up and down hills last week and pulled over when the car overheated, opened the bonnet and the fan was spinning.
I’m thinking now it might be a pressure issue within the engine or coolant pipes? The only way to cool the engine when driving is to put the heaters on full. Any help is appreciated, thanks.
