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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 05-20-2012, 12:40 PM
daw daw is offline
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Mein Auto: 1998 528i 5sp - 192K mi
Cooling System Corrosion

I noticed some evidence of antifreeze leakage around my thermostat housing, so I took off the housing and found quite a bit of corrosion. No wonder it was leaking. The housing and thermostat were replaced 20K mi ago by the dealer. You could see that they used some black sealant when they put it back together. I don't think there's an easy permanent fix for this problem. Has anybody else seen this much corrosion? I put put in new gaskets and used Permatex Super 300 sealant. We'll see if I get another 20K before it leaks again. It's a 1998 528i with 173K mi.
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  #2  
Old 05-20-2012, 12:42 PM
daw daw is offline
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I'll try again to upload some pictures.
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  #3  
Old 05-20-2012, 01:38 PM
rdl rdl is offline
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Your pictures do show a pretty rough housing all right. What does the block side look like?

First, does the engine have new (less than 4 years old) good quality antifreeze. One hopes so given the dealer changed your t-stat. Were you charged for new coolant?

If antifreeze is good, a stong possibilty is electrolysis / galvanic corrosion. See these links as a start
http://www.completeradiators.com/articles/34.htm
http://www.ve-labs.net/electrolysis-101/how-to-test
For more info Google "cooling check volt" or similar.

TIS (BMW's shop manual system) does not specify the use of sealant for the thermostat; rather it directs to renew the seal & ensure surfaces are clean and good. Given that the dealer used sealant, one suspects that a problem existed then. If so, shame on them for not diagnosing and resolving the problem at that time.

If the engine has a stray voltage problem & you need help, report back for more suggestions.
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Old 05-20-2012, 02:11 PM
daw daw is offline
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The thermostat housing is black plastic. What you're looking at it the head, where the housing mounts. The thermostat sits in the round hole on the left. I'm sure it was bad when the dealer put the new thermostat and housing in 20K mi ago since, as you say, normally you don't use sealant. Interesting that they didn't say anything about it. There is new coolant in the system now, which was put in when I did a complete cooling system overhaul 10K mi ago. The only thing I didn't do at that time was the thermostat and housing since it had just been done 10K mi prior.
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  #5  
Old 05-20-2012, 03:24 PM
rdl rdl is offline
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Oops, you're right of course. I only glanced at the picture and focused on the rough, pitted areas. With only a moderately careful look, it's pretty obvious that your picures are the block housing, not the t-stat side. For some silly reason I jumped to the conclusion that you had an aluminum t-stat housing; pure brain fade on my part.

How deep are the pits? I'm wondering if it is possible to very gently, very carefully sand to a smooth surface and count on the seal have enough compliance to take up the deviation from true flat. The seat in the round hole would be particularly tricky. Maybe smooth as best possible and then a little sealant to aid the situation? With several hours to overnight before refilling to ensure a good cure.

If the pits are too deep, perhaps carefully Dremel out the pits to clean metal and fill with good quality epoxy and smooth flat with straight edge scraper before cure time is up.

Skip the O-ring style seal and make yourself a DIY gasket from thickish, pliable gasket sheet able to bridge and fill the pits?

Perhaps, one of the better block sealant kits? Not the $5 "magic in a bottle" stuff, but the $50 to $100 systems. Except they are all meant for much harder surfaces such as a headgasket, not a rubber O-ring type seal. This would be a last hope, in desperation.

My fingers are crossed that someone else will have a better idea.

I would still do the voltage checks suggested in the prior post once you have it back together. The fact that the sealant "failed" suggests to me that some corrosion may be continuing.
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  #6  
Old 09-25-2012, 02:07 PM
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paferri paferri is offline
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Wow, just got back from the dealer and realized I have the same exact issue.

Long story short, had a complete cooling system overhaul back in 2010 along with a bunch of other preventive maintenance, and I have been through 4 thermostat housings and 2 thermostats since that time, scratching my head as to why I kept getting leaks around the housing after a few months.

I never had the leak before doing the initial replacement, and did notice some light pitting on the block face, but made nothing of it, using RTV as well as the supllied gaskets. Well after experienceing a week of overheating issues last week where needle was going 3/4, I decided to look at everything in the cooling system and was already aware of yet another small leak around the same spot on the housing, but kept topping off. After everything checked out I decided to at least re-seat the housing while I was at it, and that is where I noticed the pitting had gotten worse, not as bad as in your picture above, but visible.

Brought it to my mechanic and that is when I noticed the back of the plastic housing that mounted to the block was slightly warped and the gaskets completely melted and in bad shape. using a 2000 grit sandpaper, we decided to sand it as lightly as we could, made no difference, and did not want to make the 2 surfaces uneven when putting the housing back on.

It appears that the pitting behind the housing is etched in over time by the antifreeze itself, and only gets exaserbated once it starts leaking. The crater pockets created traps antifreeze and eats away at the aluminum as well as melting the gaskets and warping the housing itself over time, thus explaining why the same leak appeared each time after a few months when replacing with 4 different housings with brand new OEM. If you notice, these engines do get extremely hot in that area.

Bad news is it can only be fixed properly by getting a brand new head, which I may have to consider down the road if I am to keep the car for another 5 years or so. In the meantime, we decided to fill the craters with a high heat cement like epoxy that bonds to metal, then sand. Also have to get yet another new housing, and thermostat while I'm at it, then create our own high heat gasket seal instead of using OEM.

Really bummed out about it and hoping this solution will at least give me a few years before considering what to do.
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Last edited by paferri; 09-25-2012 at 02:14 PM.
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  #7  
Old 09-25-2012, 02:14 PM
daw daw is offline
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It's been 4 months and 2500 mi since I put my housing back on with new gaskets and Permatex Super 300 sealant. So far no new leakage. Not an easy thing to permanently fix.
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  #8  
Old 09-25-2012, 02:16 PM
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paferri paferri is offline
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According to my mechanic, this can and does happen with these cars at this age. Chalk it up as another poor design by BMW as the housing should have been metal instead of plastic.
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  #9  
Old 09-25-2012, 02:43 PM
cn90 cn90 is offline
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I am wondering if the BMW "life-time" coolant is inferior to Prestone LOL.

daw did the right thing, for the porous parts, a thin layer of Permatex will seal the holes up nicely.
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  #10  
Old 09-25-2012, 06:37 PM
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bluebee bluebee is offline
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My 2002 E39 had the original radiator when I took it apart in 2010 and I only saw a little bit of blue "corrosion".

Many pictures here:
- Behr radiator and Behr expansion (aka surge) tank autopsy (1)



I didn't take the thermostat apart, but it too was original and pretty clean:

So was the expansion tank (original and clean):
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See also: E39 Bestlinks & How to easily find what you need

Last edited by bluebee; 09-25-2012 at 06:39 PM.
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  #11  
Old 09-26-2012, 09:01 AM
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doru doru is offline
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Quote:
Originally Posted by cn90 View Post
I am wondering if the BMW "life-time" coolant is inferior to Prestone LOL.

daw did the right thing, for the porous parts, a thin layer of Permatex will seal the holes up nicely.
I think I read somwhere that BMW recommends changing the antifreeze every 2 years. The anti-corrosion inhibitors (among other) might "wear" out (think plastic embrittlement - my cooling stuff was in impecable shape when I changed it last year, but I know I change the antifreeze every 2-3 years).
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  #12  
Old 09-27-2012, 05:19 AM
rdl rdl is offline
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Quote:
Originally Posted by doru View Post
I think I read somwhere that BMW recommends changing the antifreeze every 2 years. The anti-corrosion inhibitors (among other) might "wear" out (think plastic embrittlement - my cooling stuff was in impecable shape when I changed it last year, but I know I change the antifreeze every 2-3 years).
You're correct that the older BMW recommendation was an anti-freeze flush every 2 years. For instance the Service booklet for my 2003 quotes 2 years.

But, the 12/2007 version of TIS quotes a 4 year interval.
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  #13  
Old 09-27-2012, 10:04 AM
jygesq jygesq is offline
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Quote:
Originally Posted by daw View Post
I noticed some evidence of antifreeze leakage around my thermostat housing, so I took off the housing and found quite a bit of corrosion. No wonder it was leaking. The housing and thermostat were replaced 20K mi ago by the dealer. You could see that they used some black sealant when they put it back together. I don't think there's an easy permanent fix for this problem. Has anybody else seen this much corrosion? I put put in new gaskets and used Permatex Super 300 sealant. We'll see if I get another 20K before it leaks again. It's a 1998 528i with 173K mi.
if less than that take it to dealer to fix both parts & labor are covered by that warranty
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