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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Fri, Jul-28-2017, 05:25:51 PM   #1
entendu
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Default Coolant leak

Started up today and got the coolant dummy light. Drove to my appointment and the light went off 2-3 minutes into it. Lifted the hood after and found this:





Confirmed it's coolant. The upper tank looks fine, upper hoses ok. Possibly the sensor o-ring?

2003 6mt, 44k miles.


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Old Fri, Jul-28-2017, 08:07:25 PM   #2
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Default Re: Coolant leak

Yea, it could be your lower hose coolant temp sensor or it also could be your water pump (worst case scenario). I would dry off the wet areas, start the car rev engine a little, maybe have someone rev it and you look to see where the coolant leak is coming from. I would never drive to my destination if I see the low coolant light on these cars. Overheat the engine just a little bit and you could blow the head gasket. Not a cheap thing to fix on this car by any stretch of the imagination.

GL with her. BTW, if you have not completed a full cooling system overhaul then may be a good time to do so.
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Old Fri, Jul-28-2017, 08:09:58 PM   #3
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Default Re: Coolant leak

I'd put money on coolant temp sensor O-ring. Otherwise, hopefully it's not something that's cracking/ ready to blow
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Old Fri, Jul-28-2017, 08:14:23 PM   #4
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Default Re: Coolant leak

I'd remove the fan and shroud and get a better look. Or take it to an Indy.
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Old Fri, Jul-28-2017, 08:58:16 PM   #5
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Default Re: Coolant leak

My coolant sensor o ring was leaking this week, just used a fuel injector O ring and quit leaking. Have a friend plug up your hole while you quick swap O rings. Pretty sure there is a DIY thread on here some where with the ACE hardware o ring part number. Or, BMW part number is 13621743299 - found here.

https://www.ecstuning.com/b-genuine-...YaAgVoEALw_wcB

Little FYI - local dealer told me they could not sell me JUST the O ring, tried to sell me the whole sensor to the tune of 71 dollars. Don't let them pull a fast one on you.
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Old Fri, Jul-28-2017, 11:30:13 PM   #6
entendu
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Default Re: Coolant leak

Quote:
ACE hardware o ring part number
Oooo where's that? I ordered one but it won't be here till monday.
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Old Sat, Jul-29-2017, 01:26:05 AM   #7
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Default Re: Coolant leak

The o-rings are shit. I'd put my bet there also
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Old Sat, Jul-29-2017, 03:02:29 AM   #8
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Default Re: Coolant leak

Quote:
Originally Posted by entendu View Post
Oooo where's that? I ordered one but it won't be here till monday.
https://www.bimmerforums.com/forum/s...g-for-59-cents

http://www.acehardware.com/product/i...uctId=59901736

Should be the same.

Last edited by Move_Over; Sat, Jul-29-2017 at 03:06:15 AM.
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Old Sat, Jul-29-2017, 03:35:01 AM   #9
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Default Re: Coolant leak

Ty guys. Will report back after I change the oring out.


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Old Thu, Aug-10-2017, 08:39:37 PM   #10
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Default Re: Coolant leak

Swapped the o-ring, but still leaking Slow leak, maybe 1/2 gallon per week.

Now I have a choice -- take it to an indy, or buy a pressure tester and take over my garage for a while.

I am mechanically inclined but I've never done coolant system work, just easy oil/brakes/rotors stuff. Should I bother trying to tackle it myself, or am I just going to get into a bigger mess?
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Discussing Coolant leak in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)