Overheating Mini One (again)! - MINI Cooper Forum

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post #1 of 11 (permalink) Old May 16th, 2019, 03:42 PM Thread Starter
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Overheating Mini One (again)!

Lots of threads on overheating Minis - but I've yet to hear this one.
My grandson and I bought this '03 Mini One with an overheating issue. We've replaced the headgasket, fitted new thermostat housing/thermostat and cap (twice - as the first cheapo ebay replacement cracked). We've researched the dreaded 2-stage fan/resistor issue, however our problem is a little different.
Using the test menu I've monitored the water temperature and when the temperature reached 95 degrees, the water boils. Now I know the fans shouldn't be switching on at this temperature. It should be OK, but it's not. The only thing I can think is that the system is not pressurising to raise the boiling point of water.
Any ideas?
Oh yes, we've bled the system (at 3 points) till we're blue in the face!

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post #2 of 11 (permalink) Old May 17th, 2019, 09:32 AM
knt
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Are you losing any coolant?

Check the radiator and water pump condition.

Have you bled the system properly?

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post #3 of 11 (permalink) Old May 17th, 2019, 07:41 PM Thread Starter
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Quote:
Originally Posted by knt View Post
Are you losing any coolant?

Check the radiator and water pump condition.

Have you bled the system properly?
Thanks KNT.
Only losing coolant when the system boils over.
The top hose quickly gets hot when the thermostat opens and the radiator quickly gets hot throughout its height - so I presume that the pump is working. Is there any other way of checking it's OK without stripping it out?
We've bled, bled and re-bled the system using all three points, but are very willing to persist at this - I know it's a real weakness of the engine.
It's strange because the temperature gauge does not go above 'Normal' yet the expansion tank spits out boiling water when the system reads 95 degrees. If it's pressurising properly, then the coolant shouldn't boil until 120 degrees plus. At 95 degrees the fan is not (and should not) kick in at this temperature.
Went out for a run in it last night and the temp stayed at about 75 deg - no problem. I just need to cure this before taking it out in heavy start/stop traffic and know that the fans will kick in and it won't boil.
Thanks for coming back to me. All help/advice greatly appreciated.
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post #4 of 11 (permalink) Old May 17th, 2019, 11:15 PM
knt
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As above, you've replaced and looked at most of the parts that are common.

Have you done a diagnostic scan to see if you have any codes?

Have you checked the temperature sensor attached to the cylinder head?

Does the fan work properly?

Other tests to do are pressure testing the cooling system and combustion leak test.

This might help with comparing your temps with

https://www.mini2.com/forum/first-ge...rect-temp.html
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post #5 of 11 (permalink) Old Yesterday, 09:55 AM Thread Starter
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Thanks again, knt.
I'll run a code check today.
I'm getting the output from the temperature sensor in the head and presuming the readings are accurate ...
The fan is not kicking in - presumably because if the engine is only reaching 95 degrees, it's not supposed to. I think the lowest temp for the fan is 105 deg. The fan works when I feed power directly to the terminals. Have looked on the Forum about the 2 speed fan and the resistor probs, but can only see one feed to the fan assembly - the pics I've seen on here show a large plug and smaller plug feeding power to the fan.
The pressure and combustion tests are beyond my capability/equipment levels - I'd need to take it into the garage for that.
And thanks for the link. I'd seen that one.
Thanks for the leads - I'll keep trying!
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post #6 of 11 (permalink) Old Yesterday, 10:35 AM
knt
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I'm sure someone with more expertise and experience than me will come along and try to help you.

The only other thing I can think of is maybe a blockage somewhere.

This series of YouTube fixing a Mini might be worth a watch

https://www.youtube.com/watch?v=Ig22...5bGxw&index=17
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post #7 of 11 (permalink) Old Yesterday, 06:12 PM Thread Starter
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Thanks knt for the info. In the youtube video the guy definitely has a blown headgasket! But I'll keep working on this one and feed back if (when) I crack it. Thanks for your advice!
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post #8 of 11 (permalink) Old Yesterday, 11:24 PM
knt
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When you replaced the headgasket, was the cylinder head still in good condition?
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post #9 of 11 (permalink) Old Today, 11:38 AM
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i deal with coolant issues a lot and have learnt the hard way that having a process you stick to to find the problems
1, first off use a sniff tester kit that will tell you if any exhaust gases in the coolant system ie black and whit test for gasket or head or block cracked, some times oil cooler or egr cooler on cars fitted with these can cause it as well, link below for a cheap kit for DIY use but works very well,
https://www.ebay.co.uk/itm/BT-3-BLOC...UAAOSwLEtYi8Gi
2, leak testing it ie the whole system should be sealed sometimes you cant see where as it only happens when engine is under load ie being driven,, so use a additive to coolant ultra violet dye that can be picked up with special torch ultra violet, this will prove where waters escapes with no guess work, link below for both dye and torch for DIY use, can also be used to find oil leaks
https://www.ebay.co.uk/itm/UV-Dye-To...8AAOSwJ7RYWWhQ
the above will give you 100% answers to what its doing, the ultra violet dye works better in the dark

Albert Einstein: The definition of insanity is doing the same thing over and over and expecting different results.
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post #10 of 11 (permalink) Old Today, 12:21 PM Thread Starter
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Hi knt, mike1967,
The head looked ok when removed - only checked it with a straight edge, but looked fine.
Mike - I've ordered the sniff test kit - thanks for the link.
There are no bubbles in the water once the system is filled and the engine is running with the cap off. All seems fine during normal running, with temp reading about 75. It's only when I put the engine under load (stationary and with revs) that the temp rises and at about 95 degrees indicated it forces water out of the rad cap. The fan has not yet kicked in (I believe it should kick in at 105 deg.

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post #11 of 11 (permalink) Old Today, 01:08 PM
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Quote:
Originally Posted by Valvebender View Post
Hi knt, mike1967,
The head looked ok when removed - only checked it with a straight edge, but looked fine.
Mike - I've ordered the sniff test kit - thanks for the link.
There are no bubbles in the water once the system is filled and the engine is running with the cap off. All seems fine during normal running, with temp reading about 75. It's only when I put the engine under load (stationary and with revs) that the temp rises and at about 95 degrees indicated it forces water out of the rad cap. The fan has not yet kicked in (I believe it should kick in at 105 deg.
if head has a crack in it when engine is cold it cold be sealed and no pressure as engine heats up the head expands and opens up the crack thats how cracked heads tend to work, need a rad cap put a type valve in it and then read with type pressure gauge what pressure is being made, up to 12psi is max before caps pressure releif valve opens letting excess pressure out to the catch tank on gen 1 cars header tank on gen 2 cars..
so if its this then another head is best fix but i have had soem good results with some stuff called steal seal if used must use a blue glycol antifreeze and must run car for a good hour after putting in to complete the process. i have customers cars that could not keep cap on after 3 years still holding water with no pressure , the odd one it just wont fix worth a punt i feel works better on cracked heads than flexible gasket failures, link below for it, worth a punt
https://www.ebay.co.uk/itm/STEEL-SEA...kAAOSwEzxYPERF

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