cooling system - what is this part?
 

on a 240D

As you can see, mine is leaking pretty badly.

Just a matter of tightening the hoses? I have no idea here..

Picture is taken from the left, if facing the car, standing right in front of the headlight, pointed toward the engine.

Also, I am aware, green coolant, no good.

http://i38.tinypic.com/2gtvh5j.jpg

What we're looking at are the thermostat and water pump housings. Thermo on the top, water pump on the bottom.

Short coolant hose. Often neglected / checked. Also, your thermostat housing may be leaking. If the mating surface is too corroded, you'll need to find a good used replacement. You do NOT want to price that piece out at the dealership. I have. They only stock them in Germany.

OK... what are the chances of a catastrophic blow of this thing?

I'll take care of this, but I am supposed to drive about 100 miles today (50 there, 50 back).

It has been leaking for a while because I have been loosing coolant. I thought it was the radiator, which has a very slow seep on the upper seem, but it seems the loss of coolant has suddenly become a lot faster, leaving drips where it is parked.

This faster loss of coolant had me looking around and that's what I found.

Depends on where it's leaking from. I spent quite some time chasing down a leak in mine. It turned out to be a pinhole in the rear of the water pump housing. But it could be a hose, a loose clamp, or some other weird thing.

Catastrophic failure is (probably) unlikely, but I would be uncomfortable driving like that. How much fluid are you losing?

One other thing - it seems to leak more when it is just sitting.

Might be short on the full evidence for this, but it was dripping a lot when I went and looked at it - car had been sitting since monday.

Went and got come coolant, put it in, still dripping. Drove a bit more, got the car fully warmed up, and now I went out and looked and there are no drips under the car.

Is it possible that when the thermo is closed, the water builds up there and leaks out faster, but when it is warmed up, the fluid keeps flowing?


CAMSNA - to answer your question - at first it was only something like a quart after a long drive, but then since monday, it seems to have lost 1/2 gallon.

I have always been checking it before any long drive lately. I drive 100 miles two days/week right now.

I had a similar leak a while back. No matter how tight I got the new hoses on there it would still leak.

I removed the thermostat housing, cleaned it up with a wire wheel and found three different holes caused from corrosion.:eek:

I ended up doing a quick fix on it with JB weld, then sanded it down and has been fine for 3 months now, YMMV.

Also, when you do get around to replacing the green stuff with the right stuff, do yourself a favor and use distilled water rather than tap. It is very cheap to pick up two gallons next time your at the grocery store.

Exactly what I did. Took me forever to find it, but the fix was quick and holding fast. Also, replace all the seals and gaskets when you do. If you need some help, PM me. I've taken my cooling system apart enough times to offer some advice.

And if you're leaking that much, I'd say don't drive it. I was leaking that much, too. A nearly invisible pinhole can cause that much coolant to flow. It's incredible. Take apart, clean thoroughly (mine was BLACK), wire brush, and inspect meticulously for holes and cracks. Could be either the thermo housing, water pump housing, or both.

But don't mess around with it. Fix it up!

+1

And flush that green crap out of there and get some G-05 at Napa, pronto. The wrong coolant can encourage electrolysis and cause pinholes, pitting, and wear of the cast aluminum parts (water pump housing, thermo housing).

If you need them, I have a couple of spare short hoses and housing gaskets. The dealer sometimes won't sell less than a meter of the hose, when all you need is two inches.

Quote ''One other thing - it seems to leak more when it is just sitting.

Might be short on the full evidence for this, but it was dripping a lot when I went and looked at it - car had been sitting since monday.

Went and got come coolant, put it in, still dripping. Drove a bit more, got the car fully warmed up, and now I went out and looked and there are no drips under the car''

I would expect this to be the water pump that leaks.

It leaks less when engine running and warm due to the temperature tightening clearances up on pump seals/shaft ??

I have seen similar on a Rover 414 but that pump leaked the other way ,only when engine was hot.

Little update on this. It is definitely the upper part (thermo housing) that is leaking. I can feel it at the seem and even see the coolant pooling in the top of the housing. It seems to be leaking at that seam and just collecting down by that short bit of hose.

Well, it could be leaking elsewhere as well, but if I am tracing it top down, the thermo housing is definitely the first place. It is wet all the way around the seam - top and bottom.

Before I take this apart, what am I getting into here?

If it is leaking around the seam, is that just likely a seal in there, or is there other things that could cause the same type of leak? I haven't ever been inside the thermostat housing.

Any suggestions on what parts I will need to/want to replace while I have it out and opened up?

be careful, the bolts that hold the upper housing on are thin, and easily broken. get the hose off, and spray with penetrating oil before you attempt to remove them.

Thanks vstech. I will do that.

Any other tips? I'll be searching for info before I do it, but anyone else wanting to throw down their 2¢ is welcome.

Have the new gasket ready that goes on the head. It's a $1 part. Put a rag in the head while you scape off the old gasket to keep the scmootz out of there. Use a new hose of course. Take a good look at the fitting that comes from the water pump while you have the hose off. It may be getting ready to go too. If so there is no better time to do it! It's leaks after you shut it down because the system is still under pressure and the coolant finds the path of least resistance. I just did one last week. Don't over torque the bolts that go into the head. It's just a coolant fitting, not a moving part. I like to use grey RTV water pump sealant for any coolant areas but everyone has their favorite flavor. By the looks of the rust around the fitting I would flush the system. I see nothing wrong with green coolant. Although I do like the color Orange. I think I'm up to 10 cents now.
Oh, and have fun. :cool:

10¢ that are greatly appreciated. Thanks Fattyman.

Answer
 

Hose, thermostat to water pump
MB# 900271042012

Gasket, thermostat housing to cylinder head
MB# 616 203 02 80

thermostat
MB# 617 200 18 15

Fastlane: thermostat
http://catalog.peachparts.com/item.wws?sku=W0133-1629646






.

Thanks whunter. I think I am actually going to expand this a little bit.

My radiator is leaking a little bit at the seam, so I decided I am just going to take care of all of this at once while I am draining the coolant.

So my plan is to take care of the following:

• Radiator
• Radiator mount kit (clips and stuff)
• Upper and lower radiator hoses (I should do this, right?)
• Thermostat
• Thermostat housing to cylinder head gasket
• thermostat to water pump hose
• New red coolant

Anything I am missing that is in the circuit of things being changed?

I have read a little bit here and there about citrus flush. Is there any need to worry about this if I am changing out the radiator?

Help is greatly appreciated. Never had to deal with the cooling system on any of my other MBs in the past. I always search on any job I am going to do, but may not realize I am missing something if I don't know what I am getting into.

get MB coolant or Zerex G05. not the DEX-COOL. *(DEATHCOOL)*

A Question about the thermostat gasket, When i replaced mine there was a slit in the old one and a hole in the new one for the little by-pass line. Which is correct or was my old one just swollen shut to look like a slit? By the way i broke off the lower bolt on the t-stat housing and had to tap a new thread so let those suckers soak over night or longer.

Thanks Quirky Mercy for the info about the bolts. That is two on "let it soak" so I better... Obviously I don't know the answer to your question because I've never been in there, but hopefully someone will know.


One last bump before I order parts. Can anyone think of anything I should get other than the following, if doing both the radiator and the thermo gasket?

• Radiator
• Radiator mount kit (clips and stuff)
• Upper and lower radiator hoses (I should do this, right?)
• Thermostat
• Thermostat housing to cylinder head gasket
• thermostat to water pump hose
• New red coolant

?

Thanks

Flush your system first so you don't circulate all the crap into your new radiator. Use anti seize on the thermostat housing bolts to keep them from seizing up again. Makes taking them off almost pleasurable! Clean the mating surfaces with scotchbrite (where the hoses mount). I like to use a little Dow DC4 grease on the O ring of the thermostat as well (make sure that the relief area where the o ring goes is nice & clean too. We would always spend more time cleaning parts than reassembling them! :rolleyes:
Take your time, save the beer for later.