Anyone know what causes this? Cap is not cracked and seal is not broken.
Tank filled to at or below MAX line. Any ideas? Thanks
Car is 2004 MCS JCW

 

If the tank didn't release pressure like this, then it would simply explode, and you would be without proper coolant levels.

Edit: by the way, as far as I know, it's normal. Mine does this all the time, especially when I drive hard in summer, just be sure to check the level and add when the engine is cold.

 

First idea is to lower the level to the proper line.

The tank is full when the cold level, with cold engine, is at the lowest line on the side of the tank.
Or looking into the tank you should see the very top of the fins higher than the coolant level.

Basically your tank is too full. It's not a recovery tank like most cars.
The level will rise and fall with engine temps and needs room for expansion.

Lower the level, clean the up the residue and put the car through its paces and you'll find that the tank will not leak any more.
Mine used to do the same thing till I lowered the level.


Hope this helps...

 

+1 use the min line and you won't get any leaks.

 

Mine did that when the PS fan started to go. Things got a little hot, and the juice just bubbled out. Makes a nasty mess.

 

Lowered fluid to MIN line cold. Raced heavily this weekend with no problems or leaks whatsoever.

Thanks for all the replies.
Neil

 

Any idea what happened to me then. The other day I noticed a small puddle under my car, a blue fluid. Determined it was coolant...jacked the car up and noticed a trail on the bottom of the tranny casing right under the clutch area. I followed the trail up to, well no where. My line in the expansion tank did not change...the cap is not leaking, and I can not find any visible leaks anywhere, and the car has not done it since.

Pretty strange...but there was at least 1-2oz of fluid on the ground that was from me...and the only fluid I could determine it was, was coolant. I don't have ATE super blue, and nothing else is blue. Ideas?

 

^^^ some times mine leaks thrue the seam of the thank

 

I'll bet that the most likely cause of your leak is the thermostat housing. Some people have had that housing leak without having any coolant showing under the car as the heat of the motor keeps it from making it to the ground.

Check the housing, just might be the culprit, especially if it was showing up after a short trip and the motor was not hot enough to burn off the residue.

Hope this helps...

 

+1 on the thermostat housing. My wife's '05 was leaking there and it sounds like a fairly common issue.

 

Thanks for the advice...I'll check it out, and keep an eye on it. So far I still haven't seen anything, it must be a pretty slow leak. I've been watching the reservoir and it doesn't appear to be loosing any either.

I've seen that Mini's have a 4yr 48k mile on like MSN, but the dealer told me I have 3yr 36k? June is the last month of my 3 years...though I do have an extended warranty...so Mini will cover this one way or another.