I changed my coolant a few weeks ago following (or during, I should say) changing the S/C oil, and replaced a slightly leaky thermostat gasket while I was at it.

After driving it for 2 days, a plume of steam developed beneath the hood as I was driving on the highway, and I discovered that I forgot to put the hose clamp back on the hose that enters the back of the t-stat housing from the reservoir! I fixed that and filled it back up again and since then have had it boil over a bunch of times. It appears that air is getting into the system and displacing coolant, forcing it upwards. The day after all this went down my car overheated, fans on, with coolant spraying all over the engine compartment out of the reservoir cap.

Since then, I've noticed a few patterns. I sometimes hear the sloshing noise, sometimes not. I've bled the system with the car off and the cap unscrewed from both the front bleeder screw as well as the secret one near the t-stat housing. A few minutes of driving and the upper hose is cold again and full of air.

A few days ago I topped off the coolant to the MAX mark while the car was hot, and I've been bleeding it once or twice a day ever since. Last night when I was diagnosing my misfire problem, I checked the coolant again. The reservoir was reading right at the MAX mark. When I unscrewed the cap, coolant rushed in almost to the base of the neck of the tank. When I loosened the front side bleeder screw until all the air was gone, the level went back down to the MAX mark. Somehow air is getting in underneath the coolant, if that makes any sense (doesn't to me, since it defies gravity).

When I replaced the t-stat gasket, I noticed a few things:

• lots of mineral deposits on the side of the head on the bottom of the t-state hole which I buffed off with WD-40 and some Scotchbrite
• The T-stat was placed in the last gasket with the vent hole pointing precisely upwards
• The new t-stat gasket appeared to have notches on the inside of the gasket that engage the flange on the t-stat, aligning it only one way
• When put in the gasket this way, the vent hole is more towards the front of the car than straight up
• When the gasket/t-stat assembly was put back into the housing, it's like the gasket was too small and had to be forced into the housing. It kept popping out of the grooves
• If I bleed the system while hot, I get a lot of trapped air out of the front hose evidenced by the amount of steam that escapes before I get to hot coolant

I inspected the housing closely last night - engine ran for a few mins but didn't get hot - and noticed a gap at the top of the housing about as thick as a sheet of paper, with a tiny amount of coolant just filling (not spilling out of) that gap. The bosses where the bolts go are tight to the head with no gap.


I surmise I have a warped housing and possibly a bad t-stat gasket. Will replacing these cure my coolant issues? The tank seems solid..ran my hand back there and found no evidence of leaks.


This is getting really old....

 

Warped housing isn't surprising. Get a new one. & don't forget to turn your heat on when bleeding. Chances are, air is still in your system. Check if you still have your low speed fan, if not, bypass the low speed resistor.

 

I always had the heat on when bleeding. I did not check the low speed fan although I heard that they go out in conjunction with (or caused by?) a faulty power steering fan.

Is it a coincidence all this stuff is happening at once? Between this and the misfire?

I've owned german cars before (VW) and this is not uncommon, but it sure is nerve-racking!

Oh, and another thing about bleeding with the car on..if I have the reservoir cap off and the car running and open the front bleeder, nothing comes out! I've never waited more than a few minutes to see if it will, but when the car's off, the air will bubble out and coolant will be right behind it.

 

Need to wait longer, if coolant is not coming out of that front bleeder then there is still air in the system.

Nik

 

With the bleed screw loosened, fill the expansion tank until fluid begins coming out of the bleed screw. Now start the engine and let it warm up, keeping an eye on the coolant level. It will likely drop as the thermostat opens. Now turn the heater on to full blast. This will allow the coolant to enter the heater core of the car.

Continue filling until there are no more bubbles coming out. . When no more bubbles exit out of the bleed screw, tighten the screw.

Now, run the engine until it reaches its operating temperature. Turn off the engine and let it cool down. Then, top off the coolant in the expansion tank to the appropriate level, if necessary.

 

How long should it take to reach operating temp at idle? It's 15 degrees F here today. Can I only start this procedure with the engine cold?

Is the bleed screw you speak of the front one, or the hidden one near the t-stat housing? I'm assuming it's the front one...

What are your thoughts about the position of the small hole in the t-stat flange? On every other car I've worked on without funky grooved gaskets you put the hole straight up and call it a day..this one seems different and I'm wondering if that's why it's taking forever to get all the air out.

Should I even bother if I have that hairline leak at the t-stat housing? Isn't that admitting more air in?

 

It will take about 10-15 minutes to get to operating temp.

Youa re wasting your time until you fix this. Yes it can and will allow air to get in.

Yes the front one.

 

I can't see the hole from your pic..is there one? That gasket looks different than mine too..mine was white silicone. I thought there was one that was better than the other..my factory one I replaced originally last year (or was it 2 years ago?) was red, looked like a viton rubber or something but it was totally smashed, stiff and brittle.

I'm assuming I should just replace the t-stat too? I mean, I'm going to be making a mess of my garage and spending more money on this car it's almost like, why not....

 

If you buy it from your MINI dealer, you should get the T-stat and gasket as an assy, and yes - white silicone gasket is the one to get.

I don't know about the bleed hole in the t-stat itself, but if you're sucking air in thru a warped housing you're defeating your purpose, so fix that too.

I've found you won't always be able to bleed all the air out in one shot, and you won't get much of anything till the T-stat opens and you get circulation. Sometimes after you've bled it if you go drive it then bleed it again, you'll get the last little bits of air purged. Do have the heater on full temp too.....

I hope you haven't blown the head gasket by overheating the engine.....but that can cause "air" in the system too, and force coolant out thru the combustion chambers.....after you fit the new t-stat and housing if you could do a cooling system pressure test to be sure you don't have other problems it might save you some diagnostic time.

It might help a bit too if we knew what year and model your MINI is.

Good luck!

 

I got the gasket from RockAuto but will probably get a new one from GermanAutoParts or another online retailer (know any others?). I avoid the $tealership like Marburg Fever.

I don't know about the bleed hole in the t-stat itself, but if you're sucking air in thru a warped housing you're defeating your purpose, so fix that too.

Sorry, it's a 2007 Mini Cooper S Convertible. I don't believe I have a blown headgasket, but I suppose it still is possible. I did a compression check and everything came up to pressure within spec both dry and wet. No other signs of coolant being anywhere near the combustion chambers - no fouling on plugs, creamy oil, steamy exhaust, etc. I'm throwing a misfire code too which began much after this did (see link above), but I'm not sure if they're mechanically related. If anything I wonder if having coolant and steam spraying everywhere under the hood has caused some of these issues. The CEL comes on and whatever the ECU changes within a few seconds after startup, the car runs fine after that. I've driven with a blown headgasket before and what's going on now doesn't sound or feel like that at all.

 

Just idling may not get the motor hor enough to bleed....
a short drive or elevated rpms seem to help make the thermostat open...allowing yours to bleed it. It has always taken me about an extra half gallon of coopant too bleed it....

 

It appears it's losing a minimal amount of coolant over time..I probably put in a total of 8oz over the last week. I have a feeling the majority of the leak is taking place underneath where I can't see it, and probably cooking off before I can see it.

Today it took half an hour to come up to temp at idle, but like I said..it's really cold out today.

Where's a good place to get a good price on thermostats? Am I allowed to ask that here?

 

Way Motor Works, Pelican Parts & other vendors on here have those.

 

I will check them out and see what I can find. I'm assuming they sell the housing too?

I bled the system last night and started up today with no swishing. About 5 minutes into driving, it came back. It's definitely sucking air from somewhere.

 

We have the kits:

All Genuine MINI:

http://www.ecstuning.com/Search/11537596787KT3/



Genuine MINI & Wahler thermostat


http://www.ecstuning.com/Search/11537596787KT4/




We also carry the OEM Genuine MINI Coolant and other that meet the MINI coolant specs.


http://www.ecstuning.com/Search/82140031133/



Thanks and I hope that helps.

 

When issue happens after a maintenance is performed i always back step on the re-installation process. You said you did serviced your s/c? How about checking the water pump area where it connects to the engine block just to see if there is any residue of coolant. One thing I recommend is to pressurize the cooling system to eliminate any leak over.

 

Because there's really no room in there to see what's going on, what's the best way to inspect this area? From what I can tell, the seal between the w/p and the block is good. I replaced the o-ring and wiped on some WD-40 during reassembly so it would go together properly.

I can post a pic of what I'm seeing on the tstat housing but it's basically a gap that's evident between the two bolt holes on the flange..looks like you can stick a thin piece of paper in there with a tiny amount of coolant filling the gap. There's white stuff all over as residue from the can blowing it's top from all the air.

Is it possible to pressure test the system myself using compressed air and a regulator at a specific pressure?

 

A preseure test is usually done with a bloodpreasure style pump, and a resiviour cap/rad cap...only a few (less than 5-10 psi) is used...and you monitor the drop/rate....generally imo more folks have hurt systems doing this...so generally not to FIND A LEAK, just to see if there is a pinhope leak....

 

Post a picture of whats going on and make sure you clean all that residue off between thermostat gasket and the housing. I could maybe guess something like dirt or residue caking up and making the seam not flush.

Thanks

 

For leak checking and filling I used an: "UView 550000 Airlift Cooling System Leak Checker and Airlock Purge Tool Kit" that I got from Amazon ~$100USD. Worked amazingly well. Need a good source of compressed air to operate the thing.

 

Try using a Leak Detection Dye. It is a colored dye that is safe to add to the coolant itself to make leaks easier to see. These dyes may be fluorescent and glow under exposure to UV lights. This can make detection of smaller leaks much easier.

Then you can use a UV Lamp is a lamp that gives off ultraviolet light that will show coolant leaks when used with a UV coolant dye.

 

[QUOTE=ZippyNH;3683768]A preseure test is usually done with a bloodpreasure style pump, and a resiviour cap/rad cap...only a few (less than 5-10 psi) is used...and you monitor the drop/rate....generally imo more folks have hurt systems doing this...so generally not to FIND A LEAK, just to see if there is a pinhope leak....[/QUOTe

^^^^Like he said.
If you have a pressure drop then search for the leak. To get an idea on how to do it watch it on You Tube. Don't forget to reference the manual in properly doing the procedure.

Before doing the test see if you can see any leak coming from that joint area while the engine is running in idle and or 3k rpm.

 

My thermostat, gasket, and new housing should be here today. I'm sure it's going to be a major PITA to get in there because of the cramped space but I hope to have it changed out this week. The coolant tank still keeps blowing its top and I'm bleeding the system through the front screw twice a day.

Last night I wiped off the tank..I wonder if one of those seams has split and is admitting air to the system? I find it difficult to believe that much air is going in from a leaky gasket (I could be wrong). I noticed no drips except from where the coolant has dripped down from the filler neck.

I should post pics - if I were to use the UV dye my engine compartment would either look like a 60's drug party or a 13 year old's bedspread.

 

If you changed a "slightly leaky thermostat gasket" you must have lost coolant during this issue and maybe overheated it too much?
If it's now worse, to the others points, go back and clean/replace the housing and surface and make sure an air leak isn't allowing the puking.
Have you checked you plug holes for any coolant as an intake manifold leak would potentially create a misfire with coolant in those holes after high heat.
If it's a head gasket issue, the coolant tank will also puk when pressure builds from the engine compression.
Do the pressure test as the problem will probably become quite clear.

 

wyldejackyl,
Did you ever come up with the answer to your cooling issue?
We had a similar situation and finally pulled the head, only to find a head crack up the # 2 plug hole and out to both exhaust valves.
It continued to puk coolant as a result of the cracked head and just kept getting worse, requiring pulling the head.
Pictures to follow.