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London town!
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Discussion Starter · #1 ·
Hello all,

have a slight issue with a car I just bought yesterday, nothing too serious but could lead to a blown engine if i dont get it sorted sharpish!!!

basically the car is over heating and I dont think the radiator fan is kicking in when it should do, so far I have managed to narrow down the following details:

- cant be the thermostat as that was replaced only a couple of weeks ago with new coolant and a system flush at the same time.
- its NOT the fan motor as if the fan is directly wired to battery positive and earth then it kicks in exactly as it should do
- it doesnt appear to be the under bonnet relay as have used as a tester on it and appears to be ok
- pretty sure there is no damage to any of the electrical cables in the fan as this was also tested.

when driving on a fast road the airflow keeps the temperature down, but when sitting in traffic or ragging it then it starts to climb pretty quickly.

My guess is a temperature sender unit or fan switch of some kind - problem is I dont know where they are located on a five or how to change them. any ideas?


ta very muchly and a mars bar to anyone who can assist!!!
 

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Yep probably the temperature sensor/fan switch if your thermostat has just been replaced.

If you connect the "TFA and GND" pins with a small length of wire/paper clip in the little black diagnostic box (passenger side under the engine bay) then the fan should come on.

If it does come on then it is probably your fan switch as the problem, which is on top of the thermostat housing at the front of the bay on 1.6s and behind the engine on the 1.8s.

http://www.autolinkmx5.com/mx-5-mk1-cooling-system-parts-211-c.asp

Autolink sell them cheap


Dave.
 

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The sender will be at the back of the engine under the coilpack area. If it's the same as the mk1 set-up, it'll be a 2 pin sender unit as the single wired sender is to the gauge.
 

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London town!
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The sender will be at the back of the engine under the coilpack area. If it's the same as the mk1 set-up, it'll be a 2 pin sender unit as the single wired sender is to the gauge.
thanks for the info, gives me the right place to look into when changing it over.

speaking of which - is it a simple 10mm spanner job with a clip on top for the electric plug?
 

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London town!
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Discussion Starter · #8 ·
Just had a rather worrying conversation with Autolink. they said it could be one of two things, either the switch at the back at of the engine or a water leak in the cabin could be affecting the ECU. the tell tale sign is dampness under the carpet. I just checked it and sure enough the carpet is damp underneath


because its a UK factory car it will also mean that I have to get a new ECU and associated electronic items to go with it.


anyone have any experience with this scenario?
 

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9 points, $20,000 and a lot of happiness.
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If it's not overheating when airs flowing my first suspicion would be the radiator.

After the engines warmed up, switch the motor off and carefully have a feel of the top and bottom pipes much difference?
What the air temp from the heater like on fully hot?

Does the car run cooler when the heaters on full wack?

Cheers
Mark
 

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London town!
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Discussion Starter · #11 ·
Hi guys,

right problem is definitely ECU but I THINK I may have managed to sort it! pretty much hundred percent certain its not the rad as the heating is really hot when at full whack and make no difference to the engine cooling whether I have the cabin blower going or not.

I pulled back the carpet in the footwell to air it out a bit and took a hair dryer to the area around where the ECU is to try and get the moisture out from behind there, then went for a drive and as predicted, the rad fan kicked it exactly when it should have done. then switched off engine for a bit, went for another drive and really ragged the car and still no cooling issues - temp needle got to half way, fan kicked in and temp sat precisely in the middle exactly where it should be.

Problem now I guess is to source the leak for the footwell although from what I gather, the drain pipes are a very common source for this when they get clogged and leak into the passenger footwell. I have left the passenger footwell carpet turned up so no more moisture gets trapped around the ECU and weather permitting tomorrow, will gut the interior near the footwell, dry it out properly and sort out what I hope is a blockage in the drain pipes which should stop the leak into the cabin - thats the theory anyway!
 

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I had a siilar issue with dampness in the passenger footwell which affected the ecu, it turned out that it was coolant coming fro the heater hoses which enter the cabin just above the passenger footwell, the 2 rubber hoses from the engine bay join onto copper pipes inside the cabin and it was from this connection that coolant was seeping and dripping down into the passenger footwell area.
It's an arse of a job to see where the pipes are, you have to be a contortionist to bend your body so you can look up there and see them...

hoses going through firewall...


and copper pipes above passenger footwell...


In my case it was the clips on the rubber hose which had been moved and put back in a slightly different position, but enough to let a small aount of coolant out over time, I fixed it by re-positioning the clips and adding extra jubilee clips just to make sure. Afterwards I checked the coolant and there was only a small amount of coolant lost.

Don't know if that's your problem, but worth a look.
 
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