Mini coolant issues, please help!! - MINI Cooper Forum

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post #1 of 7 (permalink) Old Dec 3rd, 2015, 03:26 PM Thread Starter
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Mini coolant issues, please help!!

Hi all,

I am currently having problems with my R50 2003 mini cooper.

Previously it was overheating when idle due to a leak, this has been fixed and no signs of leak.

After repairing this, all was fine for a few weeks and then it started overheating again this week.

The thermostat was faulty and this has been replaced and the car hasn't overheated since, however..

When I get back from work or from a drive the coolant expansion tank is overflowing/close to overflowing. The car keeps getting airlocks, I open the bleed valves and try to remove it before each journey but it keeps developing air locks. It isn't loosing coolant and not overheating but I don't know why it keeps getting air locks? Once the bleed screws are undone and the filler cap undone the levels in the expansion tank drop to normal and no coolant is lost through a leak.

Does it simply need to be bled "properly"? I think im doing it right, fan on low but high heat, open screws, fill with coolant until coming out of screw valves, do up screws, redo filler cap.

The fan used to stay on for ages after the car stopped, this doesn't happen anymore and as I said, it hasn't actually overheated yet I just feel like its going to, and I really don't get why the airlocks keep happening???

I have trawled all forums for answers and I just don't know what it is!!!

Any help would be great!

Cheers!!

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post #2 of 7 (permalink) Old Dec 4th, 2015, 07:58 AM
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In summer, coolant problem is too much. I also have no answer for your question.

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post #3 of 7 (permalink) Old Dec 4th, 2015, 08:31 AM
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I'm guessing you have not so much an air lock but rather a coolant system which is running hot, causing air in the system to expand (there will always be some air in there) and pushing coolant into the expansion tank.

Have you checked the actual coolant temperature via the hidden menu? Do a search on here on how to, it'd be interesting to see what temperatures you're reaching.

Next I'd check the fan operation. You mention it feels like it's going to overheat, I'd expect to hear a fan come on at some stage before that.

If the fan works (both stages), check the radiator for sufficient flow. It could be that a previous owner added some sort of leak cure to the coolant and you have a blockage somewhere.

Have the system pressure tested, if it doesn't hold pressure the coolant will boil at a lower temperature, thereby increasing the expansion issue.

Have a close look at the pressure fill cap, they have been known to deteriorate. They're reasonably low cost so it might be as well to throw a new one on. A faulty cap will cause the system to lose pressure but it won't show up with a pressure test as that's usually where the test equipment is connected up.

It might be worth adding a dye to the coolant to aid leak checking. Some of the common leak areas such as the lower corners of the radiator are difficult to spot without.

Lastly, don't forget to update this thread with your findings and hopefully the cure you found.

Hope this helps
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post #4 of 7 (permalink) Old Dec 7th, 2015, 09:25 AM Thread Starter
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Quote:
Originally Posted by roadhog View Post
I'm guessing you have not so much an air lock but rather a coolant system which is running hot, causing air in the system to expand (there will always be some air in there) and pushing coolant into the expansion tank.

Have you checked the actual coolant temperature via the hidden menu? Do a search on here on how to, it'd be interesting to see what temperatures you're reaching.

Next I'd check the fan operation. You mention it feels like it's going to overheat, I'd expect to hear a fan come on at some stage before that.

If the fan works (both stages), check the radiator for sufficient flow. It could be that a previous owner added some sort of leak cure to the coolant and you have a blockage somewhere.

Have the system pressure tested, if it doesn't hold pressure the coolant will boil at a lower temperature, thereby increasing the expansion issue.

Have a close look at the pressure fill cap, they have been known to deteriorate. They're reasonably low cost so it might be as well to throw a new one on. A faulty cap will cause the system to lose pressure but it won't show up with a pressure test as that's usually where the test equipment is connected up.

It might be worth adding a dye to the coolant to aid leak checking. Some of the common leak areas such as the lower corners of the radiator are difficult to spot without.

Lastly, don't forget to update this thread with your findings and hopefully the cure you found.
Hi mate,

Thanks for the reply!

I forgot to mention in my last post that the heater blows cold when stuck in traffic, if that matters haha.

Ahh okay. Ive seen about the secret menu on here before, do I let the car get up to temperature first then go onto the menu or do I just do it cold?

Fan operation is fine, when I'm stuck on the M25 the low speed comes on after idling for a little while and the fast one hasnt come on like it used to (used to stay on fr ages after I would park up) so that all seems fine.

I had a leak and used Radweld to plug it, it stopped the leak but could this be the problem now? Will a pressure test show all of these things up? I will have one done anyway, but just want to make sure things are missed because it is just worrying at the moment that it is going to go wrong again.

I have had a new cap and have a spare, my last one warped and let the pressure drop/leak constantly. So pressure cap is fine.

No leaks in the radiator, I noticed one before and hence the previous use of radweld which might come back to haunt me now!

Mainly, I wanna know whether the car is fine running at the moment/will it overheat again? Really, minus my own worrying, it hasnt shown any signs it will overheat, but will is it really a "problem" at the moment that the expansion tank is overflowing?

Thanks for your help.

Cheers!
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post #5 of 7 (permalink) Old Dec 7th, 2015, 09:56 AM
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Will, you have answered your own question in regards to the radweld, you need to get a new radiator and do a proper fix not a spot patch plus you will want to flush the system to remove any radweld left in there. Don't know where your from but we can get all aluminium radiators in Melb Australia for about 1/2 the price of an OEM one with a bigger core so its worth looking around.
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post #6 of 7 (permalink) Old Dec 7th, 2015, 11:02 AM Thread Starter
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Originally Posted by Milpol View Post
Will, you have answered your own question in regards to the radweld, you need to get a new radiator and do a proper fix not a spot patch plus you will want to flush the system to remove any radweld left in there. Don't know where your from but we can get all aluminium radiators in Melb Australia for about 1/2 the price of an OEM one with a bigger core so its worth looking around.
Ahh I see.. probably explained why it worked for a while and now all gone to pot.

Will it definitely be a new radiator needed or could it be something else?

I wont be able to get it done for a week or so, will it be fine until then?

Thanks again.
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post #7 of 7 (permalink) Old Dec 7th, 2015, 11:47 AM Thread Starter
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Update:

Just bought a new radiator (36) and going to fit it Saturday. Will do a flush of the system as well and hopefully that will do the trick!

Any suggestions until then? I have just been bleeding the air quickly before I drive it each time and letting the coolant level fall down from the top of the expansion tank, also driving along with the heater on full and fan on low just to open it up.

Thanks for the help so far, appreciate it!

Cheers
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