Hi. I seem to have a chronic leak from the cap of my overflow tank. I'm at 11k miles and have cleaned the tank and heat shield below several times, but every time I look there are new white crusty stains. This is definitely not the old 02-03 seam leak - it's at the cap, and I've made sure it's tightened down well.

Anyone have this? Is there some kind of gasket in the cap I might be missing?

 

I am also interested in what you find out. I am experiencing the same leak. Small, but definitely there!!!

 

The cap is also a pressure relief. If the reservoir is overfilled you will find seepage at the cap when it vents due to not having enough expansion room. Also, if you have a hidden fan issue you will have this same seepage because the car is periodically overheating.

To check for the 'hidden fan issue', which is a malfunctioning of the cooling fans due to the infamous power steering fan locking up and taking out the fuse, do this simple test. Start the car, turn on the a/c, set it to max cold and open the hood. The cooling fan should come on within 30 seconds or so, unless it's particularly cold, where it might take a minute. If the fan does not start, check the 5 amp fuse inside the underhood fuse box marked F05. If it's blown, try replacing it. It might blow once again, whereupon it's time to schedule a trip to the dealer to have the power steering fan replaced under warranty.

I dread the thought of how many MINIs are running around with the blown fan fuse. In most cases, you wont notice anything wrong until you sit idling in one place for a long length of time, as the airflow through the radiator while driving is enough to keep the engine and a/c working fine. This fan problem creeps up and is unnoticed by people (like me) until they find their cars overheating in traffic, even if they are sticklers for keeping their cars in top condition. The temp gauge will stay dead centered within a wide operating range, only rising until the engine is truly operating out of range. People like me with the Nav system and no temp gauge at all will be greeted by a light in the tach when it's too late.

There could also be just a simple case of a leaky cap or rubber sealing gasket around it as well.

 

Thanks, Greatbear. Fan and fuse are good. My first Mini had the PS fan fuse failure and left me stranded in traffic twice before I got it fixed, so I keep a close eye on the temp guage.

But you got me thinking... My car had the jcw kit and I'm wondering if perhaps the "technician" who did the install over-filled the coolant.

 

There is a more insidious cause which can create overpressuring of the coolant tank/system, and that's a blown or leaking head gasket. In rare cases, instead of 'consuming' the coolant and unable to build cooling system pressure, sometimes cylinder pressure makes it's way past the gasket and into a coolant passage, causing an overpressure condition that the cap has to continually, but slowly, vent. In even rarer cases, casting porosity in the head can cause the same thing.

 

Wow, you are the voice of doom. They replaced the head when they installed the JCW, so maybe the gasket was screwed up. Strongly doubt we have a porosity problem. I'm going in for my 10k service tomorrow, so I'll ask that they check this out generally and specifically check the torque on the head bolts.

 

I had the same problem with the coolant expansion tank overflowing. I took it in and Mini replaced the whole apparatus

 

We had ours replaced during the 1st service over a year ago because it leaked. Now, it's leaking again. Seems to leak once and seal itself up again. I'm not sure if MINI's doing anything to fix the problem but it never seems to leak enough to show a low level. Our fans work fine and I believe it leaks during full throttle high rpm accelration because I sometimes smell a sweet odor after a hard acceleration run.

 

Kapps - that data lines up with Greatbear's head gasket theory. I would assume that a leaking gasket is going to be pushing the most gas into the coolant at high rpms. Right, Greatbear?

 

In a high-boost application such as pulleyed MINIs, it's not uncommon to have 'temporary' head gasket leaks at full throttle due to stretching head bolts. The MINI engine uses torque-to-yield bolts which have an ultimate uppermost clamping force that really cant be increased much more to hold down any tighter (the bolts get torqued first to 30ft-lbs then cranked an additional 90 degrees with no regard to the actual torque value; doing this 'stretches' the bolts, putting them in their most uniform, greatest clamping strength). The gasket is of a newer design that allows quite a bit of relative motion between the head and block without damage, but some blow-by of combustion gasses might be possible.

Another issue I have been wondering about but never heard much feedback on is from those who have installed 17-19% pulleys and run to redline. This could conceivably cause the water pump to begin cavitating, causing the coolant to break up into a kind of foam. When foamy coolant moves through an engine it tends to boil much easier than 'solid' coolant. This can cause the kind of blowoff of coolant that would show up around the cap too. No one has really complained about this issue yet that I know of, and we have quite a few people running modded cars at the track pretty hard.

 

[QUOTE=Greatbear]In a high-boost application such as pulleyed MINIs, it's not uncommon to have 'temporary' head gasket leaks at full throttle due to stretching head bolts. The MINI engine uses torque-to-yield bolts which have an ultimate uppermost clamping force that really cant be increased much more to hold down any tighter (the bolts get torqued first to 30ft-lbs then cranked an additional 90 degrees with no regard to the actual torque value; doing this 'stretches' the bolts, putting them in their most uniform, greatest clamping strength). The gasket is of a newer design that allows quite a bit of relative motion between the head and block without damage, but some blow-by of combustion gasses might be possible.

QUOTE]

Mark my words, this will become a serious issue as we push higher boost. Trust me.

 

When checking the coolant level (cold) remove the cap and look inside and you should see the tops of the 'fins'.
If they are not a little higher than the coolant it's overfilled.

Hope this helps...

 

Oh, trust me. I'm fully expecting it. More to the point, I have been expecting it for a while now. 19%ers, twincharging, nitrous, you name it. People have been doing it for a while now and I have yet to hear about a particular 'limit' that has been reached where once crossed some weak link comes apart. Granted, of all the potential weak points in our 1.6s, the head gasket seems the most likely. You have a mere 10 bolts, 10mm diameter holding the head on, and it's a bi-metal engine to boot. I'm surprised there isnt a head stud kit or oversized bolts in use by now. The bottom end of these engines is almost too strong IMO. People are getting 400-500 or more HP out of the Chrysler 2.4L engines that the MINI is based on with bottom-end components not even as strong as what we have stock (cast vs forged crank, sintered vs forged rods, etc).

We may hit the first 'hard' limit someday soon, but it should not be insurmountable by any means.

 

The dealer determined that the tank/cap were bad and installed a new assembly at my 10k service. I've put on about 1k miles since then and no leaks at all. I've done quite a bit of both stop-and-go traffic and full on red line acceleration, so I think the tank was indeed the culprit. Good news.