Join Date: Jun 2009
Location: South Yorkshire
Local Time: 03:34 PM
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Bubbling coolant in expansion tank - fixed?!
Had a little problem with our 02 Cooper recently, and after a little help from this forum, have hopefully sorted it and thought I would share.
A couple of weeks ago we travelled up to Harrogate for the weekend. Very hot weather, idea for our weekend, but as we parked up at the hotel and switched off the car I could hear bubbling. I immediately opened the bonnet and could see the collant in the expansion tank bubbling, in fact it looked like it was boiling, and as a result had popped the cap off and was overrunning. I got back in and turned the ignition on, but the fan did not kick in and looking at the temperature gauge it read at the centre of the guage, perfectly normal.
We left it overnight and checked it in the morning before setting off. It had lost a lot of fluid which we topped up. I know there is a Mini dealer on the edge of town so we drove the couple of miles and pulled up to check. All OK, and we had been sat in traffic to get there. This continued throughout the hour long journey on the way back, lots of stops to check, and was all OK until our last stop where it happened again, although not as bad bubbling this time. Let it cool down and then we continued.
Checked on here, expecting symptons of a head gasket, but there were reports of coolant filler cap problems, thermostat failure, and thermostat housing cracking failure. So, thought I would have a look at this option first.
My local dealer looked up the parts for me which were as follows:
Part No. 11537829959 Thermostat Housing £14.56
Part No. 11537596787 Thermostat £20.00
Part No. 11531486703 Rad Cap £8.00
Cheaper than I thought so bought the lot. First word of advice, do not buy the cap seperately if you are buying the housing as it is included, but the dealer did not inform me of this when purchasing!
Fitting took me two hours which did include cleaning all items before refitting. First remove the airbox / filter, then remove the battery, followed by the battery holder/carrier box, which will mean removing the ecu. All sounds complicated but the battery is held in place by two bolts, one either side of the metal strap across the top of the battery. The battery case is held in place by three bolts which you will see once you remove the battery. The ecu is in a seperate compartment in the same plastic unit, and you will need to to tip the unbolted battery case 90 degrees clockwise and the ecu will slide out.
The thermostat housing is held in place by 3 bolts which are easy to get to once the above have been removed. This also gives easy access to the pipes which will need the clips opening/pulled back so that they can be slide off. Carefully remove the old housing and note which way round the thermostat is fitted. I cleaned everything up the block, put the new thermostat into the housing which was a nice snug fit so it held in place while I put in place and put the bolts in place. I tighted each bolt a little, then went around all three again to make sure it wasnt pulled tight at an angle. Refitting of everything was the reverse of above.
Everything back together, I mixed a 50/50 coolant/water mix and filled up through the rad cap opening at the top of the thermostat housing. I also opened by a couple of turns the bleed valves on the top hose and the one at the back to the left of the bottom of the battery housing. Started filling and as the lower valve at the back ran continuously I tighted up, and then did the same with the upper hose. I continued to fill and after filling to the top each time it bubbled very slightly and the water level lower, so continued until it bubbled no longer. Then I squeezed the upper hose with my hand a little which made the collant bubble, so again, repeated until it bubbled no longer. Fitted the cap, ensuring correctly fitted and tight, then filled the expansion tank with the same mixture until just over the MIN mark. Push the cap back on.
Started the car and let it sit ticking over for almost an hour. No bubbling, or overheating, the temperature gauge settled at the normal position half way up the gauge and all ran fine. I was cleaning the car out and in the garage so kept a close eye on it all the time.
All seemed OK so next time used was my regular trip to the coast for the kids, and to see my parents, a 200+ mile round trip. My trip over included lots of stops to check the levels, but was all OK so I continued. Did not bother stopping on the way back but when I got home I did top up the expansion tank a little, not because it had lost anything but I like to have the level just at the top of the MIN lettering.
The car has now completed about 400 miles since the new parts fitted and no problems to report so, fingers crossed, all fixed.
For the cost of the parts and the time if you are mechanicaly minded, I would consider this again as the first port of call to diagnose the problem.
I will keep you updated if anything happens.