Intermittent Coolant Leak

n2siast · 01-02-2022, 11:03 AM

2012 35i xDrive, 70K Miles - vehicle seemed to develop an intermittent coolant leak, which I believe is exiting through the Expansion Cap, through the little hole on the top of the tank through the cap.

Saw a few drops a a little over a week ago and added some coolant to the tank, which was a bit low. After that, didn't see any leaks for about a week, until yesterday, when I went into the garage, saw s little puddle on the floor.

Leak isn't consistent, so I eliminated the Expansion Tank itself, which I actually replaced a few months back.

Water Pump and Thermostat were replaced twice since 2018.

Anyone experienced this intermittent leak? Any ideas on what it could be?

Serf27 · 01-03-2022, 11:53 AM

How did you rule out the expansion tank?
My tank was cracked on the bottom and I couldn’t see the leak, I replaced it and the new one cracked too. I had to replace it again and now it’s fine.

n2siast · 01-04-2022, 12:34 PM

Quote:

Originally Posted by Serf27

How did you rule out the expansion tank?
My tank was cracked on the bottom and I couldn’t see the leak, I replaced it and the new one cracked too. I had to replace it again and now it’s fine.

I assumed that since it was only intermittent that the tank wasn't/isn't leaking. It's been filled to the max line the last few days and haven't leaked.

My assumption is that if there was a crack on the tank itself, then it would continue leaking, but that's not the case.

I've seen some information that mention a possible Water Pump issue and if the pump goes out every so often, that could explain the pressure buildup and causing the coolant to bubble over through tank cap.

Serf27 · 01-04-2022, 12:52 PM

The tank I replaced on my e70 would leak huge puddles sometimes and then other times not leak.

n2siast · 01-05-2022, 04:11 AM

Quote:

Originally Posted by Serf27

The tank I replaced on my e70 would leak huge puddles sometimes and then other times not leak.

Thanks, man. I'll investigate the tank a bit further. At this point, I"m hoping it's the tank as that will be a quick easy fix.

n2siast · 01-12-2022, 02:25 PM

Update, in the event anyone is tracking down a mysterious leak.

In my case, it didn't turn out to be the expansion tank, it was/is actually the Heater Control Valve that developed a small crack and would leak intermittently, primarily when the heat is on.

I took off the undercarriage panel and I saw some coolant residue on the hose coming off the valve and down towards the subframe, as I looked further up, I saw a bit of coolant dripping from the valve, thus identifying my leak.

I also ran a diagnostic check and received an error code for the Driver Side Water Valve (Heater Control Valve), I assume the leak and code have some correlation to each other.

New valve on order and should be a quick 20 minute fix.

So, all this to say, this is another item to check if chasing down any phantom leaks.

01-02-2022, 11:03 AM	#1
n2siast Lieutenant 76 Rep 405 Posts Drives: E93 335i M-SPORT Join Date: Aug 2013 Location: Richmond, VA iTrader: (9)	Intermittent Coolant Leak 2012 35i xDrive, 70K Miles - vehicle seemed to develop an intermittent coolant leak, which I believe is exiting through the Expansion Cap, through the little hole on the top of the tank through the cap. Saw a few drops a a little over a week ago and added some coolant to the tank, which was a bit low. After that, didn't see any leaks for about a week, until yesterday, when I went into the garage, saw s little puddle on the floor. Leak isn't consistent, so I eliminated the Expansion Tank itself, which I actually replaced a few months back. Water Pump and Thermostat were replaced twice since 2018. Anyone experienced this intermittent leak? Any ideas on what it could be?
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01-03-2022, 11:53 AM	#2
Serf27 Brigadier General 2851 Rep 4,322 Posts Drives: 335i Join Date: Apr 2018 Location: Sitting in a BMW. iTrader: (-1)	How did you rule out the expansion tank? My tank was cracked on the bottom and I couldn’t see the leak, I replaced it and the new one cracked too. I had to replace it again and now it’s fine.
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01-04-2022, 12:52 PM	#4
Serf27 Brigadier General 2851 Rep 4,322 Posts Drives: 335i Join Date: Apr 2018 Location: Sitting in a BMW. iTrader: (-1)	The tank I replaced on my e70 would leak huge puddles sometimes and then other times not leak.
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01-12-2022, 02:25 PM	#6
n2siast Lieutenant 76 Rep 405 Posts Drives: E93 335i M-SPORT Join Date: Aug 2013 Location: Richmond, VA iTrader: (9)	Update, in the event anyone is tracking down a mysterious leak. In my case, it didn't turn out to be the expansion tank, it was/is actually the Heater Control Valve that developed a small crack and would leak intermittently, primarily when the heat is on. I took off the undercarriage panel and I saw some coolant residue on the hose coming off the valve and down towards the subframe, as I looked further up, I saw a bit of coolant dripping from the valve, thus identifying my leak. I also ran a diagnostic check and received an error code for the Driver Side Water Valve (Heater Control Valve), I assume the leak and code have some correlation to each other. New valve on order and should be a quick 20 minute fix. So, all this to say, this is another item to check if chasing down any phantom leaks.
	Appreciate 0 Quote