Car is a R53 Mini Cooper S.


Background information:
Previous owner traded in the car because it had coolant loss that was diagnosed as a cracked head. The car would go through coolant very quickly and I would need to add coolant about once every 2-3 days to be able to catch it before the car would over heat due to low coolant.

I did a cylinder leak down test and compression test and got poor results on both tests. So I pulled the head and it pressure tested OK so I just replaced the headgasket. The headgasket looked like it was leaking between the coolant passages and the combustion chamber on cylinders 3 & 4 so I figured the problem was solved.

I found that the clamp for the lower radiator hose was loose and replaced it, no more leak there. There do not appear to be any leaks anywhere else on the car (I've thoroughly inspected everywhere I can, not just peaking around lightly or looking for coolant on the ground, which there has never been since I've owned the car).

The system does not appear to have any air in it either, as I can open both coolant valves and coolant comes out immediately, so I'm past the thought that there's just air trapped somewhere.

Coolant does not seem to be going into the oil either. The oil is not "frothy" or "foamy" as it would be in that situation, nor has the oil level gone up as it would if there was as much coolant as I'm losing mixed in.

Now, the problem I'm having is that I'm still losing about a pint or so of coolant every day (30 mile commute). Or, if I fill it to the top of the baffling in the coolant tank, it's about half way to empty from there after I get home and check it the next morning once it's fulled cooled down.

I'm stumped by what the problem could be and I was hoping someone could offer some insight.

 

Sounds like the coolant might be leaking into the combustion chamber rather than the oil, and be getting burnt....i guess that is the worst case...
Maybe the radiator is failing...look at the sides where the plastic sides are crimped to the metal core...the heat set crimp tends to fail over time....and you might have a slow leak there...loosing that much coolant, can you smell it or see any steam?!

 

I had my girlfriend rev up the engine while I watched/smelled the exhaust and it did not smell sweet or have any steam coming out.

I'm going to do another leak down test on it tonight and see where that gets me.

 

Be careful with leakdown tests...sometimes folks overdoo the psi and cause issues...remember, normal operating preasure...
if leakdown is ok, i thinking it is a cracked head...the heat open up the crack...
but before you do that, look around for white resudue..that much loss should leave some if it it a leak....also perhaps look at the lines to tge heater core by the firewall, and make sure carpet is dry around the heater core....
I would really suspect the rad though...my mini guys keeps a few aftermarket ones in stock...says the new modern, non welded/brazed plastic crimped to the core desgin is cheap, but has a limited life...

 

I'm using a professional snap-on cylinder leak down tester for the leak down tests. Luckily I work at a BMW dealership.

I did a coolant pressure test tonight and pressurized the system to 15psi. After about 3 hours it had fallen down to 11psi. I could not see any leaks anywhere and I removed the cover to the heater core and everything was dry there as well. The carpet was not wet.

I'll attempt to do a cylinder leak down test on Saturday, I'm really hoping all goes well with that.

Tomorrow I'm going to take the front end off and remove the radiator and inspect it for leakage.

This is really getting frustrating.

 

I hope you find it...you took a chance it would be a easy fix....but atleast you have the expertise and tools to do it. Just look forward to the fun when it is done!!

 

PS
have you looked at the area around the thermostat and its housing...
Location might be near the intake for the vents...and it tends to blow back....common leak, mini introduced an improved gasket on it in 2005...that and the coolant tank on the s is very common...then the rad on 8- 10 year old mini's
Good luck agin.

 

Well I did another leak down test today. Got about 10% leakage on cylinders 1-3 and about 12% on cylinder 4. I filled the coolant tank full to the top and no bubbles came through.

I was thrilled by this because prior to replacing the headgaaket I was getting about 30-40% leakage on cylinders 3&4.

I did tighten up the bolts for the thermostat housing
They weren't particularly loose but they all snugged up a bit, I haven't seen any leak from around that area though.

I guess I'll have to wait and see what happens.

 

Have you done a coolant system pressure test?

 

I have. The first time I did it I found a leak on the lower radiator hose and replaced the hose clamp. After that I could not find any leaks, but would still have very slight pressure loss over 3-4 hours. I even went so far as to pull the radiator fan assembly and A/C condenser from around the radiator to see both sides.

Due to that result, I re-did a leak down test to see if the headgasket job had somehow failed but it passed a leak down test perfectly.

 

Well I'm still having the coolant loss.
I did a 300 mile road trip on Sunday. Before the trip I topped up the coolant to right above where the baffling stops. Half way through my trip (150 miles) I checked it again and there was about 1cm of baffling showing. I topped it off and on the second leg of the journey it used about the same amount.

I still show no exterior leaks and checking the oil shows no signs of coolant.

Where do I go from here? If I take it in to a Mini dealer, what are they going to be able to do that I'm not..

I'm at a total loss here and it's getting frustrating because I don't want to put any money into the car if this is going to be some absurd repair.

 

No idea if this will help, but have you checked the heater core? Before mine was replaced I had to add coolant a few times. It wasn't anything like the volume you're describing, though. Good luck!

 

Check for a cracked coolant tank as well, they are known to go bad at the seams.

 

Not sure how a head is pressure tested but does this also check for warpage?
Could the head bolts be stretched?
Was the deck checked for warpage?

Also how was it originally diagnosed with a cracked head?

 

I took off the access panel to the heater core and everything seemed dry with no signs of leaks. I did not however remove the heater core to check it. According to the previous owner, the heater core was changed due to it leaking, so unless that was a lie (wouldn't surprise me) it SHOULD be ok.

I suspected that 1st and replaced the coolant tank. It does not appear to be leaking at all (yes I've checked it even though I replaced it).

I took the cylinder head in to a machine shop and asked them to pressure test it as well as check for warpage and correct if necessary/possible. The head ended up pressure testing fine and was not warped.

I did use brand new head bolts and since they're stretch bolts I'm not really sure how to check to see if they're stretched or not.

I'm not sure how it was originally diagnosed with a cracked head, but when I got the car I did a cylinder leak down test that indicated 30% leakage on cylinder 3 and 40+% leakage on cylinder 4. So I figured it was either a cracked head or a bad head gasket. Mind you the leakage was partially into the coolant system.

 

I removed my radiator tonight and it's going in for a leak test in the morning. It doesn't really seem to have any signs of leakage but it's less than $20 to test it and the labor to swap it is my time which I have enough of right now.

While it's out of the car I have a really nice view of the front of the engine and the water pump. There doesn't appear to be any leakage coming from the water pump area and all of the hoses are dry with no signs of seepage from the clamping point.

I have been talking with the BMW technicians at my job and have been advised to look at the spark plugs, if I'm burning as much coolant as I seem to be burning, at least one spark plug should be clean due to "steam cleaning" of the burning coolant in the cylinder.

Here are photos of the spark plugs, I apologize for the size:
Cylinder 1:


Cylinder 2:


Cylinder 3:


Cylinder 4:


They all seem pretty normal to me, none is really cleaner than the rest. I'm not sure about the white deposits on them. Google searches seem to indicate that it's more-or-less normal. They were changed less than 4000 miles ago when I bought the car.

I've also been advised by a mini technician that I should check the heat exchanger. This seems irrelevant in my situation because if it was leaking there I'd have coolant in my oil and vice versa, which there doesn't seem to be. The coolant is always blue (mini/bmw coolant) and the oil is always normal in color (not milkshake looking like it would be with as much coolant in it as I'm losing).

 

When you pulled off the head, did you also have the block deck checked as well? The head may be straight, but if the deck is warped a little, it can still cause these issues. I would add a UV dye to see if there is any external leaks, or if you pull the head back off, if there is any dye pooling up around an area that is lower/warped.

I don't like the idea of using TTY ( Torque To Yield) bolts who's heads twist, stretch, and become the weakest part of the bolt on F.I. cars. Oddly enough, I've seen stretched bolts cause this problem in F.I. cars a couple times. Besides the head lifting because the bolt heads are weak and stretch, The bolts can pull up the threaded area because bolts pull up on the deck and threads, creating a "Bulge" around where the threads are, preventing proper clamping force against the head gasket, yet your torque wrench will give you correct readings. (Hell, I even did a N/A Mustang 3.8, which the 3.8's are known for the threads bulging up since they are right on the deck surface, preventing proper clamping, and the rest is history...) So if you have to take the head back off, I would A: have the deck checked for straightness. B: have the bolt holes chamfered if they are bulging after the deck is planed. C: Use ARP studs and nuts, not TTY bolts. Remember, studs push down, bolts pull up....

 

I wanted to use ARP studs but I figured since I wasn't taking things apart multiple times that head bolts would do just fine. I also didn't suspect that the block would warp since I've never heard of that happening to iron blocks before.

 

Any metal will warp, it's just aluminum is more prone to it, and because aluminum and iron expand at different rates, this combination is more prone to some sort of head gasket failure, followed by warpage.

 

Closed by OP Request.