Bubbling coolant in expansion tank - fixed?! - MINI Cooper Forum

First Generation Faults & Fixes MINI faults and fixes 2001 - 2006

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post #1 of 7 (permalink) Old Jun 6th, 2010, 08:52 PM Thread Starter
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Talking 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.

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post #2 of 7 (permalink) Old Jun 26th, 2015, 11:52 AM
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Thank you for your post I had the same problem but with mine

I replaced the housing stat and cap refilled 50/50 and everything was fine until a week later it started to bubble up again thro the expansion tank the oil is okie and the temp is normal I've checked for air locks thro the cross screws I'm but confused now could it be the water pump? But that's joint on to the belt??

Please help thanks

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post #3 of 7 (permalink) Old Jun 28th, 2015, 10:23 PM
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post #4 of 7 (permalink) Old Jun 30th, 2015, 08:22 PM
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Hi I've had a problem with my coolant tank mini cooper s 2003 I've replaced the tank but the water keeps coming out by the cap and the water is bubbleing and I'm worrying please help
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post #5 of 7 (permalink) Old Jul 1st, 2015, 10:17 AM
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Originally Posted by boxednfresh View Post
sorry yes i have also replaced that everything was fine till again yesterday the samething happned as i was stoped in traffic bubbling and then temp started to go up as i have leaned before i put the heaters on to full hot to let the engine cool down but then after a while the hot air became cool not hot

So i then stoped at a safe place let the car cool down 30 mins and then i came to see that the bubbling had caused the water to very low

i was scared that the head may have taken the cause but the oil seemed ok

i toped up thwe water and its fine now but i know it will happen again
what i noticed that when i switched the car off only then the fan came on very high and noise

but not when the car was running

im very sure my frist low fan is not working and this is the cause can some please help me in how and what to do is it the resistor next to the fan do i replace that or will it go agian?? i have red up someone moding the wiring to when the low spped fan comes on the high comes on i hapy to do that but i have me clue of the wiring and How to?? put my A/C is not working???

the 5A fuse is intacked not blown
i rwally need soem help here please as it is very hot and i dont want to cook the engine im a rover lover but hate the headgasket route


or even can i wire the high speed fan on when the car starts?? and off when car gos off?
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post #6 of 7 (permalink) Old Jul 1st, 2015, 10:18 AM
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Originally Posted by Howiee View Post
Hi I've had a problem with my coolant tank mini cooper s 2003 I've replaced the tank but the water keeps coming out by the cap and the water is bubbleing and I'm worrying please help
i would start first to replace the state and housing but see if your fan works???
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post #7 of 7 (permalink) Old Nov 21st, 2016, 06:15 PM
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Hi all, I know this is an old post, but I had the same problem with my r53 jcw yesterday, and today I've sorted the problem of the coolant tank bubbling over,

1. Change the coolant cap.

2. Replace the thermostat.

3. Replace the coolant temperature sensor.

4.Check and change fuses and relays for coolant system.

5. Check that both high and low speed on the fan is working.
You can do this by using a 12v battery and two lengths of wire, earth to eath, live to small live wire for slow speed and live to live on thick wire for high speed.

Mine wasn't working on low speed so replaced that with a salvage part, also do a check on the replacement parts before fitting.

Drop the old coolant and replace with new and bleed the system from one point on the coolant pipe above the radiator, and an 8mm bolt next to the thermostat housing.

The tank now doesn't over heated and the fan kicks in when it should keeping the system cool.

Hope this helps.

Sent from my HTC Desire 620 using Tapatalk
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