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Bacon Unicorn
174 Posts
Discussion Starter · #1 ·
Fan doesn't seem to work, leading to overheating when in traffic or on decent run.

This could be something as simple as the thermostat switch being broken (quite a common thing).
Looking at the front of the engine you'll see the thermostat housing poking out the front with the top rad hose attached to it. On top of this is a switch with a wire coming off it, this is the switch that usually fails.
Be sure that the engine has cooled before removing it. Unscrew the old one and replace with a new one, they're not expensive (under £20 ish).

Underlying reasons why the fan motor has failed?
The fan motor bearings can go, which can result in a slow turning fan. This is often the case with a car that is constantly overheating. Overheating could be the usual; blocked radiator, airlocks. But MX-5s (particularly 1.6s) also have a problem in the thermostat housing, where the bypass lines can block (with cylinder head machine swarf). At a cruising speed, the engine will run hot, and the fan will cut in, when in fact, the fan should only be coming on in standing traffic.

Still overheating with new stat? Coolant reservoir bubbling and fan not switching on in traffic?
If there's combustion gases in the coolant then it's possible that the head gasket is failing.
Check for plain water in the system and lack of or no coolant. Flush out the system and replace with deionised+50% coolant.

So, it's flush, replace the thermostat, new rad cap, clean out thermostat housing bypass lines. Use a HOAT antifreeze (pink); it will lubricate the water pump. Run up, and bleed off the coolant system. If its still overheating, then it's time to get the radiator checked.
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