Engine overheating problem when idle - MINI Cooper Forum

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post #1 of 8 (permalink) Old Jul 21st, 2014, 05:58 PM Thread Starter
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Engine overheating problem when idle

Hello

I am having a problem with the cooling system on my 05 cooper.
When in traffic, i notice the engine fan come on pretty much straight away. I have to top up the water in the reservoir once every 2-3 day.

I left it on the drive earlier, with the engine running after 15mile journey, and the fan kicked in, then off, then back on, then back off, then back on again and the reservoir erupted with water and air. I switched the engine off again, and waited for it to cool down and for the fan to switch off.
Switched the engine back on again, and it did the same thing, except on the third fan cycle, i noticed air bubbles bubbling into the reservoir tank. I checked the engine temp and it was climbing into the red, so i switched the engine off.

The engine didn't suck back in any of the water from the reservoir tank, could i have a faulty thermostat?
I bled the system not so long ago and the problem still remains.

Thanks
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post #2 of 8 (permalink) Old Jul 22nd, 2014, 07:02 AM
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I recommend a head gasket check as it sounds like you could have exhaust gasses pressuring your cooling system. You may not have mayo in the water, but that would be if oil contaminates it, which in turn would not over pressurise the system.
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post #3 of 8 (permalink) Old Jul 23rd, 2014, 10:24 AM
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hi
thees cars are a nightmare for the coolent problem try bleeding it again might take 3 or 4 times before its got rid of all the air my cooper did. one night i drove 10 miles or so and it over heated and lost all its water got to a petrol station filled it back up and it justed kept ****ing out wife came with 10 2 litre bottles full of water and every 1 mile had to keep topping up until we got it back home. next morning got up expecting major problems i only filled it back up one time water stayed in and never had a problem since
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post #4 of 8 (permalink) Old Jul 24th, 2014, 08:22 PM Thread Starter
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Thanks for the replies. I will try bleeding it again, my dad used to be a mechanic and he also said that the bleeding could be an issue because its all crammed into such a tight space. But he also did say that it could be leaking exhaust gases into the coolant. His mate is a mechanic so he is going to do a BLOCK test on the coolant (already has the kit). Might be a while away tho till this happens but i will let you know if your interested.
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post #5 of 8 (permalink) Old Aug 16th, 2014, 02:17 PM Thread Starter
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It wasnt leaking exhaust gasses into the coolant after testing the fluid.
I replaced the thermostat to see if that was the issue, but the problem continued.
I believe it is the temperature sensor since the temperature always remains in the middle. This results in the boiling of the coolant around the engine block, and screwing with the ECU. Also the engine hunts on idle, which could also be because of this.
Any thoughts?
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post #6 of 8 (permalink) Old Aug 16th, 2014, 04:56 PM
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Temp sensor on right of head gasket, down side of air filter box. (On Cooper S anyway).

I had same issue with a recon head I got with dodgy sensor, new one resolved it straight away.

Mine went redline first turn on, took a while for the internal temperature to rise enough to open the system. I kept the nipple open and re-topped up no issue at all.
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post #7 of 8 (permalink) Old Aug 18th, 2014, 11:32 AM
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Is the low speed fan working correctly? If you can hear the fan when driving the this may be the high speed fan which means the car is near to overheating.

There is a large resistor which controls the low speed fan operation but it's not uncommon for this to burn out and stop the low speed fan operating.

There is a massive thread on northamericanmotoring.com titled "low speed fan we need a fix" unfortunately I'm not able to post links yet.

The gauge in the car is controlled by the ecu and NLT tracks the temperature up to the normal temp. It does not show the actual temperature even if the car gets hotter. It will eventually rapidly rise up to the red sector but it is no use as a guide to show if the engine is running a bit hot.

You can get the actual temp to show on the speedo whe you turn on by entering the diagnostic menu which might be worth doing to see what is actually happening.
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post #8 of 8 (permalink) Old Aug 28th, 2014, 07:05 PM Thread Starter
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Quote:
Originally Posted by Colin RedGriff View Post
Is the low speed fan working correctly? If you can hear the fan when driving the this may be the high speed fan which means the car is near to overheating.

There is a large resistor which controls the low speed fan operation but it's not uncommon for this to burn out and stop the low speed fan operating.

There is a massive thread on northamericanmotoring.com titled "low speed fan we need a fix" unfortunately I'm not able to post links yet.

The gauge in the car is controlled by the ecu and NLT tracks the temperature up to the normal temp. It does not show the actual temperature even if the car gets hotter. It will eventually rapidly rise up to the red sector but it is no use as a guide to show if the engine is running a bit hot.

You can get the actual temp to show on the speedo whe you turn on by entering the diagnostic menu which might be worth doing to see what is actually happening.
Thank you, this has been a great help. The temperature dial doesnt seem to go above the middle even when the reservoir is boiling up. So i will definitely have a look on how to get the true temperature up in the diagnostics menu.

I dont believe i have fixed it. After changing the temperature sensor, the problem still occurred.
I have a feeling it is the head gasket. The BLOCK test showed no carbon emissions in the cooling fluid however, so its a real mystery at the moment.
You can also see the bubbles coming up in the coolant when you take the cap off (air bubbles bubbling up a little) which makes me think its the head gasket.

After fitting the new temp sensor, i raced it round the block putting load on the engine, and then reved it on the drive, sure enough it erupted. It hasnt happened since though, but i have done smaller journeys worth about 90miles, which is promising, but i still feel like the problem is there because it cant just go away. Perhaps the smaller journeys allow the pressure to be relieved before the next one.

Is the smaller fan for the power steering fluid? I dont notice the fan when driving, its usually when ive stopped at a light it will come on and off. The engine does 'hunt' on startup.
My father is an ex-mechanic, so I will query him about it too.
Its a shame my mechanical engineering degree doesnt cover general mechanics, i think it definitely should.
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