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Discussion Starter #1
Hi. I have a 2004 R50 Cooper.

I have a problem with the coolant temperature, when I use the car it always looses some coolant level.

I changed the thermostat, the thermostat housing, the coolant cap and the coolant temperature sensor (the one on the block of the engine), I tested the cooling fan and it works fine on both stages.

I checked the oil and the coolant and they are OK, the car hasn´t lost any power at all.

The problem is that the radiator fan kicks in too late. I did a test on my garage, I put the car on test mode showing the temperature on the instrument cluster.

The temperarure started to raise normally, at certain point I started to acelerate the engine and the temperature started to raise, the problem is that when the coolant reached almost 100ºC, the coolant level on the reservoir started to raise almost getting to the cap, then the radiator fan started to run until the temperature reached 105ºC.

When the radiator fan kicks in everything started to become normal, I repeated the test and the same happened.

When I use the car with the A/C on it never looses coolant (because the radiator fan is always running), so I think the water pump is OK.

What can I do? Is there another coolant temperature sensor? Is there an adjustment of the temperature point for the fan?
 

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The engine cooling fan runs on low speed at 105C, High speed cuts in at 112C and runs until coolant drops by 4C where it reverts back to low circuit. As the coolant temp increases, the coolant expands, therefore, when the engine is cold, the coolant should be on the Min mark, when the engine is up to running temp, the coolant should be on the Max mark.

That's why its called and expansion tank (your coolant tank) and many make the mistake of adding coolant to the Max mark when the engine is cold. The space left from the Max mark to the top of the tank is to prevent loss of coolant should the car start to overheat so if you over fill the tank, your not allowing recovery of coolant back into the system as the engine cools and it will overflow the tank and be wasted.

When you use the AC, the lowspeed circuit will always be running once the AC pressure reaches 8 Bar and the highspeed cuts in when the AC pressure reaches 18 Bar.
 

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Discussion Starter #3
Thank you for your answer. I thought it was a reservoir tank, not an expansion one so I refilled every time to the max marker and everytime it lost some coolant, now I know why. :)

I think everything is OK now.
 

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Thank you for your answer. I thought it was a reservoir tank, not an expansion one so I refilled every time to the max marker and everytime it lost some coolant, now I know why. :)

I think everything is OK now.
Fingers crossed its sorted :), reservoir / expansion tank, bit of a muchness really as its doing both tasks. I would be checking it daily from cold and when hot for a couple of weeks, sounds a bit paranoid but if there is still an issue you will pick it up well before it becomes a serious problem. When I have had my fluid drained, I check from cold and hot every day for at least a week just to be sure.

When I was in the military, we would check coolant, oil, brake fluid, PS fluid, tyres, windscreen washer, Instruments, wipers, horn, lights etc every time we signed for a vehicle and every morning regardless.

I have managed to cut back to once a week now in the civilian life :)
 
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SeanC
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