Mysterious coolant leak on the M3, any ideas???

Turk

Lt. Ron "Slider" Kerner
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Jan 21, 2008
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So took the car out tonight to strats, on the way home I floored it once in 2nd gear. About a mile later low coolant light goes on so I turn into Wendy's and pop the hood. Coolant sprayed everywhere. Call my buddy, he comes with a flash light and we search for a leak for 30 minutes, can't find anything so we fill the coolant with half gallon and start the car to see if anything sprays and nothing. And another half gallon and the coolant is now reading max lvl. Start car and nothing. I drive the car all the way home with zero problems. Wtf!
 

Outlaw

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Jul 24, 2009
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Hood wasn't popped. I'm going to have to venture to say that it was the cap. Like I said on the phone, I had the same problem with the galant, but with the cap tightened and a slower leak than yours... but same principal to it all.

Oh, and sorry about being short on the phone, rest of the house is asleep.
 

Mike K

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Apr 11, 2008
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The coolant tanks like to split. The tank on mine seeps and every couple days it will end up emptying the reservoir and then will only take enough coolant to fill the reservoir (about a gallon). You can't see a crack; just a spot where fluid is leaking under pressure. It's a common E60 issue and since you use the same coolant and your overflow tank is made out of the same material, I'd venture a guess that it's the same problem.
 

Mike K

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Apr 11, 2008
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If his cap is anything like mine, it would never leak out of there unless the cap was loose enough to almost fall off. We don't have the traditional push-down and turn radiator caps. We have giant plastic things that spin 6 or 7 full turns to come off. Mine stays pretty much fully sealed right up until the last turn.
 

jprophecy

Regular
Jan 9, 2012
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MY guess would be the cap was on enough for the system to pressurize and yet loose enough that under pressure it sprayed out of the cap all over. Was it all over the underside of your hood and over the engine compartment? I have seen it happen before with loose caps.


You then fixed the problem when you refilled it and tightened the cap back in place.
 

10sec

I haz dat teddy bear smile.
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Jul 26, 2008
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It was my GTP, it ran fine. I towed it to Phat's house telling him what happened, coolant in the oil and all. The car ran perfectly fine, even after pulling the heads off, the gaskets didn't even look blown. Mystery. Probably could have changed the oil a bunch of times and went on my way.
 
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