I don't think I understand what you mean.

 

rubber gasket has a slot cut in it that the thermostat fits into. The gasket actually fits around and onto the thermostat, then the assy is placed into position in the housing.
But be sure to check nearby hoses and connectors first.

 

Next question is, exactly how much needs to be done to re-place (not replace) just the thermostat and not everything else I did before? Obviously I need to detach lower radiator hose to drain coolant and presumably the connections to the thermostat (although maybe not?). Am I still going to need to take the whole front end off and slide the radiator forward and all that? Assuming I have to detach the upper radiator hose from the thermostat I imagine I probably will need to do all that again to have room to re-attach that hose.

 

You do not have to put the car in front end service to replace the thermostat housing. I wouldn't even detach the lower radiator hose as that will drain all coolant. I think most coolant will stay in place since the housing isn't the lowest point. It will get a bit messy but just hose it down afterwards.

 

no front end service needed.

put big catch bucket under car and pull the housing off. i dont think the hoses even need to come off

 

this

 

found a pic.

rubber on both sides of metal thermostat

 

Ok thanks once more! Fingers crossed. I'm still having trouble picturing being able to wrestle thing thing out and back in while still connected to the hoses but we'll see.

 

Be sure to position the bleed hole in the thermostat properly too. Not as hard as it seems to get it in there.

 

I'm still not quite clear on how I had no leaks the first 3 days and then the leak started up again and that was that.

 

Best practice to put therm+gasket in first and then install housing over it, like this:



or better to put therm+gasket into housing and then slap the whole thing in like this (this is what I did the first time):

 

Yeah I don't see how to do this without front end service mode....I can't even get the airbox out because the duct doesn't have enough room to clear it lol.

edit - there was a bolt I missed that wasnt in the pics, duh

 

Put it in the housing first, it has a ridge where it sits in.

 

Ok it appears the gasket was already correctly on the thermostat so I guess I'm at a loss. None of the hoses appear to have leaks anywhere I can find. I had torqued housing bolts to 9 ft/lbs.




I'm assuming what looks like light blue paint everywhere is dried coolant? That housing and those hoses are all new so it definitely seems to have started spattering from somewhere - not just leaking and running down - a few days after my "fix".

 

the gasket seems like its on the thermostat right.

have to be sure it stays in place as you put the housing back on

what do your temps look like after warmup?

 

The pic is how it looked when I removed it so it seems like it was in there all good.

Temps were fine while we were driving.

Maybe I should just get a new housing and gasket to be safe. A little worried I won't be able to wrestle the upper radiator hose back on it without the space from the front service mode though.

 

Ok this just occurred to me:

When I had the whole car apart the first time, all hoses disconnected and coolant drained -- the reservoir never emptied; I was told because it's not pressurized.

So how come once the car was back together, coolant filled, driving, everything seemed fine, once back in the garage the reservoir might be a little lower, but then overnight its level would drain dramatically? How was the reservoir repeatedly, night after night, losing level sitting in the garage, when it did NOT lose level day after day of sitting in there with every hose disconnected, no radiator in place, etc? (Also the drips under the car never came close to accounting for how much level in the reservoir was lost)

Also the coolant in the pic posted a couple posts backs sure looks like spatter and not drip; it's splotched on the fill neck, the hoses, etc. So I'm assuming that must have happened while it was driving and under pressure? And definitely seems like the housing could be the only place that could have had the leak? Or am I thinking about this all wrong?

 

Yep, the housing could have a small crack or brass set in sleeve could be working off the plastic.

Make sure the surface is really clean. MINI over the years on the Gen 1 MINIs updated the gasket to a different rubber, they used to leak like crazy and the changed the part under wahler. Which was oem at the time. They went with a more silicone based gasket.

https://www.ecstuning.com/b-wahler-p...537596787~wah/

I think the yellow gasket is the older rubber design.

 

I think what your seeing,

When you had the car apart, the coolant was drained down past the thermostat housing hence why the coolant level never dropped as this is the main source of your leak. Now that its back together the coolant is leaking out the thermostat housing / gasket hence the continual drop from vacuum / gravity pulling coolant down.

That is 100% splatter from pressurized coolant, if it was a slow leak or drip you'd have pockets and pools of blue not this splatter which is evident on the rear coolant hose.

ECS is on the right track, the thermostat housings are famous for cracking even on R53s.
- Thoroughly clean it, and thoroughly inspect it for any hairline crack. Also as stated check the brass sleeves are properly seated into the plastic.
- If the housing is ok, unfortunately the gasket is likely the source.

Clean any build up off the head with a green scrub pad before assembling again
Install the gasket into the thermostat housing first. Take your time and ensure its fully seated, if not you'll get an improper torque reading and likely not get the thermostat tight enough to hold pressure.

Best of luck!

 

Great info as always! I'll update the thread with the big finale once it's settled.

 

They make some replacement therm housings in cast aluminum now but not sure about that one with the filler neck cast in, but do check. If it's available, I would certainly upgrade, they don't cost much.

 

I’ve never seen a metal thermostat housing for the R50. If one exists, it likely would have come out within the past couple of years.

 

Yep we have metal for the R53/R52 S/JCW. Nothing metal for the R50/R52 Cooper (non S). Just OEM and aftermarket plastic options.

 

Ok after about a week of my wife driving it every day, the level in the reservoir has not dropped! So I guess the coolant leak is fixed, although there IS still a small drip of coolant in the garage. Not really sure where that's coming from but at this point I think I'll leave it and just monitor the level every couple weeks.

Next project is power steering leak. I think I'll start with replacing the clamps at the reservoir (although at first try I don't even see how this is possible, after unbolting the reservoir there is still no give in the hoses to lift the reservoir out enough to reach those clamps, much less put new ones on) just to see if this alleviates it before getting into full hose replacement which sounds like a PITA.

There is also oil leak (I think, and mechanic who did diagnosis quoted us for valve gasket cover replacement) but her last oil change was Feb 2024 and the dipstick level is still good so...?

 

Clamps can help for a while, but my experience has been that you’ll have to break down and do the hoses at some point. They’re really not that bad if you put the car on stands and pull the front wheels and inner fenders so that you can go in from the side.

I haven’t noticed reservoirs being a huge issue. I have heard of them potentially leaking as a result of a compressed gasket, but I’m not sure how true that is. They also have a vent in the cap that keeps them pretty much perpetually oily. Just BMW things.