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Discussion Starter #1
Quick synopsis...I replaced the failed thermostat on our 2000 M5...tore some o-rings, and coolant leaked all over the place. Those o-rings are a hoot. Took it back apart, installed all new o-rings after thoroughly cleaning all surfaces, used sil-glyde and it went back together nicely. Started the car, thought it was all good, but then noticed coolant dripping off of the back side of the engine (one drip every 30 seconds) with the engine running (after about 5 minutes of idling). That was 2 months ago, and the car has been sitting in the garage waiting for me to get back to it.

Finally got a chance to work on it again tonight. Took off the intake so I could see into the valley, hooked up a pressure tester, charged the system to 20psi for 15-20 minutes looking for a leak. No signs of a leak anywhere! Nothing in the valley, nothing from the hoses at the rear of the engine, nothing leaking under the car. The pressure tester didn't loose any pressure while it was charged. It seems too good to be true, so before putting the intake back on and running it again, is there anything I should check? I appreciate any insights.

Thanks,
Paul
 

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Could it just be residual coolant that was pooled up in the valley from when the o-rings were torn?
 

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or, did you spill some coolant while refilling the reservoir and happened to then drip down to that location? Doesn't seem like this would be the case since you let the car idle for 5 minutes, but if you spilled a bunch maybe? jeez this sucks!
 

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Discussion Starter #4
I suppose it could have been residual...It's what I'm hoping for. The car is up on jack stands right now so I don't have to bend over as far to work on it. I think I'll put it on the ground and pressurize the system again. I read somewhere that there is a coolant seal at the back side of the block covered by the bell housing...I sure hope it's not leaking in there!

I'll post back what I find. Thanks for the responses.
 

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Discussion Starter #5
I just went out, put the car down, and pressurized it to 20 psi for 20 minutes It didn't leak at all. I guess I'll put the intake back on this evening and run it.
 

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I do hope I'm wrong but it's possible that you have leak at #4
It's not common but coolant leaks do develop there and it's usually when engine is fully warmed up.
You can only change that gasket when doing the clutch or rear main seal due to limited access and I considered it doing it preventative when I did my clutch but the bolts are known to break during removal so I left it alone.
 

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Discussion Starter #8
Update: I rinsed out the valley of the engine and blew it dry. Put the intake back on, took it for a ride, and have no leaks. I believe the slow drip I was seeing was residual coolant (as you guys suggested) that was getting blown by the fan, moved by vibration, etc. toward the weep hole at the back of the engine. I feel a bit foolish that I pulled it back apart after it was fixed, but we live ad learn. I know I learned a good deal. if anyone has questions about replacing a thermostat, let me know. And as an aside, my mechanic friend told me that 20 psi was too much pressure and that the rule of thumb is 16 psi to test for coolant leaks.

I'm happy to have the old beast back up and running!.Thanks for the input. I appreciate it.

-Paul
 

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Good on you to figure it out! As I was reading the post from the beginning, my first thought was the coolant was leftover from the previous leak. A lot of fluid can get stuck in the valley. Go enjoy the beast with some carefree miles!
 

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Discussion Starter #10
Thank you Tim!

BTW, I'm very impressed that you've driven the 2000 M for 295,000 miles in NY state! Growing up in Central NY, I watched our vehicles rust away to pieces. My buddy from Georgia would say, "they disappear like soap in a bathtub!"
 

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Thank you Tim!

BTW, I'm very impressed that you've driven the 2000 M for 295,000 miles in NY state! Growing up in Central NY, I watched our vehicles rust away to pieces. My buddy from Georgia would say, "they disappear like soap in a bathtub!"
Haha. Yeah, the salt is brutal. I drove that car in 6? winters and the car was always from the Northeast. It came from the tristate area before I bought it. I don't drive it in the winter anymore. It does have rust bubbles around the gas door (common) and recently both rear quarters where the wheel arc meets the rear bumper. The under side of the car is very clean so I plan to have the rust repaired and the whole car painted. It's not going anywhere, so I don't even consider cost of work vs what the car is worth. Too many memories made over those miles!
 

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technician117

Do I have something to share for you about rust repair. Looking to do a post about it and share.

About Coolant leaks - I think I may have a really really small leak - can smell coolant inside the car sometimes.
Not enough where I have to refill often. I watch the cold level on the reservoir and have had to add may be 100ml per 20K km's type of thing.
 

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keep monitoring it though.
 

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Discussion Starter #15
Too many memories made over those miles!
Absolutely! Memories are priceless, especially in an iconic car like the E39.

keep monitoring it though.
I agree. Each time I drive it I check underneath, and each time I am just as excited to see it dry. My son and I took a 4 hour drive on Saturday and it ran like a top. Thanks again for your inputs. This community is a significant reason why I've kept the car for so many years.

-Paul
 

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I just wanted to ask BMW about your comments of the bolts braking when removing the coolant cover behind the flywheel. I've never heard of that. I was thinking of replacing that gasket while I was in there next time for a clutch job, but now starting to rethink that. Anyone else have problems with those bolts?
 

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Hi Paul, I thought I was such a bad *** changing the thermostat on my M5, I got all the parts, washers, o-rings, and was really clean and careful. I was not going to be the numskull who tore the o-ring and leaked coolant everywhere. I even used a coolant extractor to remove the coolant and didn't spill but a drop! Oh, I thought I was so cool, cleaning everything up, changing the 2 little hoses back there, there wasn't a BMW technician in Germany who was as good as me! then I took it for a little drive, I changed the MAF's too, and I was so pleased with myself until I pulled back up the ramp to my little hobby shop and saw fluid everywhere, ugh!

There was now way I tore an o-ring, I was so careful...., well with less finesse and less time, I pulled the thermostat out and the passenger side ring was ripped. I ordered the new ring from advance auto (they now own Worldpac) and I'll pick them up tomorrow morning on my way to work. My second attempt will be with a little more humility and hopefully the results will be better- oh, please!

Any suggestions for the second time around are most welcome!
 
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