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

Turk

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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!
 
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Turk

Turk

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The cap felt kinda loose when I first took it off to refill if.
 

Outlaw

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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.
 
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Turk

Turk

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Is it possible for around a gallon of coolant to spray out of hte cap?
 
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Turk

Turk

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Is that a yes mook?
 

Outlaw

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Yes it is possibile. '00 Cherokee had to add over a gallon because it was spraying from the cap. I'd replace the cap to be sure, I replace them every two years or so as it is.
 

C.Evans

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Check the connection of the radiator hose ends on each of the hoses. They are held in place with a clip and sealed with an o-ring instead of the traditional spring or hose clamps. I had a BMW do this to me once.
 
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Turk

Turk

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Check the connection of the radiator hose ends on each of the hoses. They are held in place with a clip and sealed with an o-ring instead of the traditional spring or hose clamps. I had a BMW do this to me once.
If the connection came lose, why would it hold water for the drive home?
 

Mike K

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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.
 

Outlaw

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If the connection came lose, why would it hold water for the drive home?
High pressure from the pull as opposed to normal driving the rest of the way. That's a good point Chris, I forgot BMW's have that setup.
 

C.Evans

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Don't know, just something to check. My vote would be to put it under 16lbs of pressure and let it sit to see if it leaks.
 

Mike K

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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.
 
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Turk

Turk

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I hope it ain't cracked! The thing is, it sprayed EVERYWHERE. The underside of the hood had spray on it.
 

jprophecy

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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.
 
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Turk

Turk

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It was all over everything for the most part.
 

1quick

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when I was 16 I took a radiator cap off when the car was hot, it basicly emptied the radiator, so I would say very possible if you cant find it leaking from anyware else
 

Dasfinc

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X2 on a cracked tank. My old SHO Taurus had a hairline crack in a radiator end tank that took me a month to find because it only leaked under load/pressure.
 

10sec

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Could have lifted the head, the combustion made it's way into the cooling system, blew coolant everywhere, and now it runs "fine", at least for the time being. Happened to me before, but it wasn't a BMW. :dunno:
 

ilikemtb999

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It wouldn't smoke at all if that happened? I'd feel like he'd have water in his crank case or combustion chamber.
 

10sec

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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.
 

Shocker

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Well can't help you fix it, but now your going to have that odd smell for awhile.
 

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