Mystery Coolant Leak - MINI Cooper Forum

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post #1 of 7 (permalink) Old Jan 16th, 2019, 11:30 AM Thread Starter
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Mystery Coolant Leak

2003 R53 140,000 miles

Coolant "dumps" out over the head shield for the headers. Splash pattern indicates that it's coming from somewhere around the reservoir. It already has an aluminum aftermarket reservoir. I pulled the reservoir completely out. No cracks in the tank, and the inlet and outlet hoses are perfect. Replaced it, filled it with coolant, watched it get up to temp, reved the engine to get it hot, no leaks at all. Left for an hour and noticed a small puddle of coolant under the tank on the heat shield.

Now when the first leak happened on the way back from work, I would say that it dumped out vs leaked. I was able to park the car within 60 seconds and the reservoir was empty.

I figured, since the aftermarket tank doesn't come with a cap that the original owner just used the same cap. So the cap would be from 2003 and may have failed. To me this seemed like the only option. No leaks anywhere in the area, so the only option would be the old cap has failed and can't support the pressure anymore. Not the case. Purchased new cap. This morning the same thing happened, except on a lesser scale.

No chocolate milk either, so it's not leaking in the oil.

Complete mystery.

Someone please enlighten me. I'm going nuts over this.

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post #2 of 7 (permalink) Old Jan 16th, 2019, 01:44 PM
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Originally Posted by rich0611 View Post
2003 R53 140,000 miles

Coolant "dumps" out over the head shield for the headers. Splash pattern indicates that it's coming from somewhere around the reservoir. It already has an aluminum aftermarket reservoir. I pulled the reservoir completely out. No cracks in the tank, and the inlet and outlet hoses are perfect. Replaced it, filled it with coolant, watched it get up to temp, reved the engine to get it hot, no leaks at all. Left for an hour and noticed a small puddle of coolant under the tank on the heat shield.

Now when the first leak happened on the way back from work, I would say that it dumped out vs leaked. I was able to park the car within 60 seconds and the reservoir was empty.

I figured, since the aftermarket tank doesn't come with a cap that the original owner just used the same cap. So the cap would be from 2003 and may have failed. To me this seemed like the only option. No leaks anywhere in the area, so the only option would be the old cap has failed and can't support the pressure anymore. Not the case. Purchased new cap. This morning the same thing happened, except on a lesser scale.

No chocolate milk either, so it's not leaking in the oil.

Complete mystery.

Someone please enlighten me. I'm going nuts over this.
below link best way put a dose of ultra violet dye in water run it up use a special ultra violet light will find the leak easy in the dark, links below
https://www.ebay.co.uk/itm/Ring-RLD2...frcectupt=true
light torch
https://www.ebay.co.uk/itm/UV-ultra-...frcectupt=true

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post #3 of 7 (permalink) Old Jan 17th, 2019, 10:17 AM
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I returned a new Aluminium tank as the supplied cap what not a pressure relief cap, just a straight screw on and the original had a different thread so could not be used on the new tank. A non pressure relief cap will cause over pressure in the system and may then causes leaks. I suspect this is where your problem lies. I went back to the original style tank which can be bought very reasonably. The leak could also be coming from the heater pipes that run into the cabin. Lastly you mentioned inlet & outlet pipes, The original only has an inlet pipe?
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post #4 of 7 (permalink) Old Jan 17th, 2019, 12:50 PM Thread Starter
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There are coolant hoses that go into the cabin??? I've never seen that. I'll have to check to see if that's a possibility.

The car has been running with the aluminum tank for the 2.5 years I've had it without issues until now. Also, the cap and replacement cap were both MINI OEM.

Naturally the tank would have a return coolant hose and an exit coolant hose.
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post #5 of 7 (permalink) Old Jan 17th, 2019, 12:58 PM
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There are coolant hoses that go into the cabin??? I've never seen that. I'll have to check to see if that's a possibility.

The car has been running with the aluminum tank for the 2.5 years I've had it without issues until now. Also, the cap and replacement cap were both MINI OEM.

Naturally the tank would have a return coolant hose and an exit coolant hose.
no point guessing what it could be only way to know for sure is to test it, ie by far best way is put a dye in it see where it comes out,, if it dont then head gasket sniff tester next test, link for this below, its all about a process and method of finding faults, no two jobs can be the same is best mind set to have
https://www.ebay.co.uk/itm/BT-3-BLOC...frcectupt=true
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post #6 of 7 (permalink) Old Jan 19th, 2019, 09:02 AM
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There is also water pipes that run along the back of the engine down low which lead to the the oil heat exchanger to cool/warm the engine oil. The pipes are steel and mine had rusted through.
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post #7 of 7 (permalink) Old Jan 26th, 2019, 11:27 AM Thread Starter
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Resolved!

Ended up taking it over to Way at WMW. The low speed engine fan resistor was bad and there was a small leak due to a wrong clamp. The engine was getting hot enough for the coolant to boil over, but the stupid Mini temp gauge wasn't showing it.....

Needless to say, I ended up going with a scan gauge.

Thanks everyone!
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