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Old 07-07-2012, 07:19 AM   #1
mikhit
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Could the thermostat be leaking here?

03 325xi with 105000 miles here. About 1000-1500 miles ago, I replaced a leaking thermostat, which I assumed was leaking from the gasket or unevenly torqued thermostat bolts. The majority of the coolant had accumulated on and around the lower bolt under the therm.

Last night I noticed that the new therm was leaking too! In disbelief, I inspected the source of this leak thoroughly, and although the pattern of accumulated coolant is the same as before (on and around the lower bolt), it appears as though the source of the leak is where the electrical socket housing actually enters the therm housing right in front of the therm.

Unable to get a clear picture from inside the engine bay, I dug out the old therm to diagram what is going on. The red circle indicates the point where the leak appears to originate, and a clear line of dried coolant runs down to the lower bolt (with red arrow) where the majority of the coolant presents.

What is most strange is this old therm, which I never cleaned up actually has the same pattern of dried coolant, with substantial residue deep inside that recess indicated by the red circle. Other than some leak at this location, I cannot imagine how so much coolant could accumulate inside this recess, which is the highest point of the dried coolant. Even if a constant drip of coolant was hitting the belts and spraying upward (incidentally, I caught the leak very early and there was little evidence of spray inside the engine bay), I still cannot justify how so much coolant is working its way into this one spot, without completely soaking any other parts of the therm.

So, I have not found any information regarding leaking from this location (all other threads point to gasket or torque issues). Is it possible to leak from the location I have suggested? Is there some sort of weep hole here to help relieve pressure if it builds up too much (therefore indicating I have some other issue in my cooling system)?

Any help is greatly appreciated.

Thanks!
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Old 07-07-2012, 08:19 AM   #2
mikhit
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Anybody have experience with this?

Summary: Could thermostat be leaking from red circled area in attached pic? It's where the electrical housing enters the therm.

Thanks!
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Old 07-07-2012, 08:22 AM   #3
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Should not leak at all.

What brand thermostat did you use for replacement?

Did you put a new cap on your ET lately?
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Old 07-07-2012, 08:31 AM   #4
mikhit
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Quote:
Originally Posted by Stinger9 View Post
Should not leak at all.

What brand thermostat did you use for replacement?

Did you put a new cap on your ET lately?
Therm is BMW. ET got a new cap when replaced a little over a year ago (also BMW parts).

There is no way for this part of the therm to leak? OR could it, under massive pressure (presumably what you are considering in asking about the ET cap), be rupturing some seal in there?
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Old 07-07-2012, 10:15 AM   #5
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It is possible to have a failure there (at the heater element/connection area), but it's Not very common in OE/OEM thermostats in such a short time of usage from a brand new unit.

On the other hand, it is known that in off-brand units, ie: china-knockoffs > Aluminum thermostats there could be random failures in that exact area... such a pity.
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Old 07-07-2012, 10:17 AM   #6
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Is the area around the lower bolt on the engine block pitted or slightly irregular...then possibly the turbulance from the cooling fan pushes coolant upwards into the wiring socket.
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Old 07-07-2012, 10:34 AM   #7
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If its less than 2 years old and you bought it from the dealer and actually is leaking there, it should be under parts warranty.
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Old 07-07-2012, 11:43 AM   #8
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Quote:
Originally Posted by mikhit View Post
Therm is BMW. ET got a new cap when replaced a little over a year ago (also BMW parts).

There is no way for this part of the therm to leak? OR could it, under massive pressure (presumably what you are considering in asking about the ET cap), be rupturing some seal in there?
Yes, I was wondering about pressure, but not after you told me you have a new cap.
If I were you and not knowing anymore than you do, I'd be inclined to put yet another thermostat on there and hope for the best.
I have to think you got defective units.
And torque down evenly when you install, and not too tight.
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Old 07-07-2012, 12:13 PM   #9
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Quote:
Originally Posted by BimmersGarage View Post
It is possible to have a failure there (at the heater element/connection area), but it's Not very common in OE/OEM thermostats in such a short time of usage from a brand new unit.

On the other hand, it is known that in off-brand units, ie: china-knockoffs > Aluminum thermostats there could be random failures in that exact area... such a pity.
So even though I am using an OE part, and although uncommon, it is reasonable, based off my findings, that this would be the location of the leak? What causes this part of the housing to fail? Just a defective unit?

Quote:
Originally Posted by 330ciandr6 View Post
If its less than 2 years old and you bought it from the dealer and actually is leaking there, it should be under parts warranty.
Yes. Will definitely make use of the parts warranty here.

Quote:
Originally Posted by Stinger9 View Post
Yes, I was wondering about pressure, but not after you told me you have a new cap.
If I were you and not knowing anymore than you do, I'd be inclined to put yet another thermostat on there and hope for the best.
I have to think you got defective units.
And torque down evenly when you install, and not too tight.
Is there an easy way to test the cap? I am going to install another therm, but I'd like to take every measure to prevent this issue from recurring. Should I consider the pressure issue further before this install?
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Old 07-07-2012, 12:36 PM   #10
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Originally Posted by mikhit View Post



Is there an easy way to test the cap? I am going to install another therm, but I'd like to take every measure to prevent this issue from recurring. Should I consider the pressure issue further before this install?
I'd just try another thermostat. Doubt your cap is causing this.
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Old 07-07-2012, 03:17 PM   #11
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Quote:
Originally Posted by mikhit View Post
So even though I am using an OE part, and although uncommon, it is reasonable, based off my findings, that this would be the location of the leak? What causes this part of the housing to fail? Just a defective unit?
Well, yes it could be simply the luck of the draw on your part... to receive a defective unit.

However, it's also the design... as far as I can tell that could lead to a higher odds of it leaking at that location. Disclaimer - I'm by no means an automotive parts designer but...

If you look closely on the thermos, there are two different versions of the "mounting" of the heater element:

This one, exactly like yours (the "wiring conduit" wraps around the outside of the thermo housing and goes into it from the "front")


*This design could be the problem?

and

Here the heater's wiring harness/connector goes straight into the thermo housing from the top.
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Old 07-07-2012, 03:27 PM   #12
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Two types

Behr is a quality manufacturer

Wahler is original manufacturer
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Old 07-20-2012, 03:12 PM   #13
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A quick update, and follow-up question:

After noticing the coolant leak, I cleaned everything up carefully to monitor the thermostat just so I could be certain about the origin of the leak -- at the "heater element/connection area." Being that I hadn't lost much coolant (coolant level indicator slightly less than half way between min and max), I never topped off with fresh coolant.

Now it has been almost 2 weeks, and there is no evidence of any leak from the therm at all.

I am wondering if, back to Stinger's remarks about the ET cap and pressure, this should still be a consideration? Could I have somehow previously had too much coolant (ie the coolant level indicator be inaccurate), thus resulting in too high a pressure in the system causing the therm to fail and leak as described previously? Or is this much to complex an analysis?

I want to make sure I've discounted every possible explanation because I will have to bring the car to BMW in order to make use of the parts warranty before I can replace the therm, and I don't want them to hit me with $130 diag fee because there was some underlying cause to all of this....

Thanks for your input!!
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Old 07-20-2012, 11:42 PM   #14
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The best guess if you overfilled the ET would be that the pressure built up too high and caused the ET cap to relieve some pressure, then the coolant would spill onto things looking like a fresh leak.
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Old 07-21-2012, 12:18 PM   #15
mikhit
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Quote:
Originally Posted by Stinger9 View Post
The best guess if you overfilled the ET would be that the pressure built up too high and caused the ET cap to relieve some pressure, then the coolant would spill onto things looking like a fresh leak.
I too would expect this. however, my leak very clearly originated at the therm. I have no reason to suspect that I overfilled the ET, but it is curious to me that now that coolant level is slightly lower (while still within normal range), the therm leak appears to have disappeared.

Your comment about the ET cap several posts back just got me thinking along those lines....
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Old 07-27-2012, 05:24 PM   #16
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My 2 month old wahler is leaking from the same location. I just noticed it today. This is my second wahler thats been leaking from the same area. -_-
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Old 07-27-2012, 06:22 PM   #17
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My 2 month old wahler is leaking from the same location. I just noticed it today. This is my second wahler thats been leaking from the same area. -_-
I'm still not sure how to justify how this has happened. Would be my second OE therm too. However, since I cleaned it up, and haven't touched the coolant level (which is on the lower side of the accepted normal range), the leak has ceased. This really confuses me.

For now I'm leaving it alone. Unless it starts to leak again, I will wait to replace until I have some other work to do. Just can't get myself excited about doing cooling system work for the third time this year!
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Old 07-27-2012, 06:54 PM   #18
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However, since I cleaned it up, and haven't touched the coolant level (which is on the lower side of the accepted normal range), the leak has ceased. This really confuses me.

For now I'm leaving it alone. Unless it starts to leak again, I will wait to replace until I have some other work to do. Just can't get myself excited about doing cooling system work for the third time this year!
Understand not wanting to go there again. I did my entire system three years ago and have not had to even add water since. Guess I'll do my coolant this fall just to be super safe even tho it tests fine every time I check it with CoolTrak.
http://www.cooltrak.com/

Sometimes these things will leak upon install, and then self seal along the way.
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Old 08-08-2012, 08:04 PM   #19
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I have gone through 2 wahlers leaking in the same place (failed within a month of installation), along with one on my dad's vehicle (all leaking at the front connection and trailing down to one of the lower bolts ).... I think they just came out with a crappy batch, I bought mine from bimmerspecialist..... really getting tired of taking off the fan etc then having to pay more $$ to fill it with the bmw coolant after dealing with sending it in and getting warranty. If I get the opportunity I'm going to switch to different brand.
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Old 08-08-2012, 09:22 PM   #20
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What's odd is BMW has a TSB saying to swap any broken thermostats from Behr to Wahler...I got a Behr one and I love it.
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