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HI.

My car started overheating after a few minutes on the freeway today. Nursed it home (it cooled more when running at speed) and opened the bonnet to find the fan not running. I bridged the ground and fan terminals in the diagnostics box and the fan ran. This then appears to be a case of a faulty thermoswitch (the plastic top half actually snapped when I went to pull the electrical assembly off the top of it). I thought I would confirm this was the only issue and ran the car after it had cooled down a bit (was running just over half way on the temp gauge), bridged the fan again so it would run, but the temp continued to climb. This leads me to believe the fan is not the only problem .

I fitted a new water pump during its last major service and the car has not had any issues since, so I doubt the water pump is the issue. Water seems to be moving between the overflow and the radiator, so there is no blockage there. It also has a relatively new radiator cap (fitted at the same time as a new radiator top).

Any suggestions on other possible causes would be appreciated, as I am stumped! I will try to find a thermoswitch to fit tomorrow, but as the temp kept increasing after the fan was manually ran I think this may not be the major problem.

Thanks

Blocked radiator, faulty pump, pumps belt is missing, fan isnt working properly, blocked cooling gallery etc

Dann

Thanks Dann... After I fit the new thermos witch, will go hunting for other problems. I know the fan was working previously, so it would be a bummer if it has died at the same time as something else .

There's a fan relay, but that might be what you're referring to as a thermoswitch:
viewtopic.php?f=55&t=50097

I grabbed the new fan thermoswitch as well as a new thermostat (may as well replace it and the gasket at the same time, just in case it is closed in the wrong position). I am hoping it is just the fans.... Will fit it on the weekend and post an update.

The fans only kick in when the temp gets too high, so I doubt they are your problem.
The new thermostat is a good starting point as well as a good radiator flush and new coolant.

if i ever think the cars running too hot i turn the aircon on to trip the other fan to work. i have a temp sensor on my top radiator hose and when it hits 60 i turn aircon on and it drops to 40 almost instantly. but i have a 42mm asi radiator too.

40c?

its bloody cold at the moment with 20c ambient temps. plus the top radiator hose probably isn't the best place to put the sensor, its just the easiest.

40c is way way too low.

Dann

vrmmmpshhh wrote:its bloody cold at the moment with 20c ambient temps. plus the top radiator hose probably isn't the best place to put the sensor, its just the easiest.

Your thermostat wouldn't be opening at those temps. What does the in-dash temp gauge say?

indash temp gauge is the same as it always has been at around 40%. the thermo fan works as usual too running every 2-3 mins while at idle. driving around the temp gauge for the top radiator hose is around 60 but the entire setup is freshly installed so ive been playing around with different settings seeing what happens. when i press the a/c button the gauge drops to 40 almost instantly. im happy with the results, the ASI radiator/fans do not sit flush like the factory and i have no undertray. removing a/c probably helped too.

http://www.miata.net/garage/cooling_system.html

Normal temperature gauge indication puts the needle just slightly to the left of center for the 1.6 and just slightly to the right of center for 1.8 engines. It is quite common for the needle to climb quite high (without overheating) on a hot day, though there are some steps you can take to reduce the possibility of overheating and keep that needle close to normal.

Note: The stock water temp gauge on the Miata in a way is linear. It's just that between 180°-210°F, it will stick to that 11AM position. If you ever climb over 210°F, you will notice the needle will climb up slowly. At about 210°-220°F, it will sit at the 12 oclock position. At 230°F, you can see the gauge start to move to the 1/2 oclock position.

180f = 82c

I think your aftermarket gauge isn't working correctly. 40-60c your thermostat won't be opening and the car won't be up to temp.

Your cooling fan won't be activating until the mid 80's

HI all. I fitted the new thermostat and thermofan switch this morning. Flushed system, but everything in there was pretty clean as it was done when I had the radiator top replaced. The thermostat was the problem, which was being shown up when the fan switch also died. Now all is working well. Fans are working, but only cut in after some spirited revving, as the engine temp is staying nice and low.

Thanks for all of the advice!