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Old 02-12-2018, 02:08 PM   #1
Drives: World's First Invisible 2012 GTI
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Unusual Coolant Expansion Tank Issue

So, it's been cold here in SEPA. Car was driving a little sluggishly. Thought it might be the fuel pump as I'm over 100k and due (overdue) to replace. Was just under the hood a month or two ago replacing the engine fuel filter and the headlights. Nothing unusual.

Car has had a vague coolant smell after driving for probably over a year, but no leaks. Have mentioned it at service appts before, but nothing ever came of it.

The other day, a pretty cold morning, I started the car and was greeted with the dulcet tones of the highest-pitched warning sound I've ever enjoyed, telling me to check the coolant level.

Sure enough, expansion tank appears to be nearly empty. Also evidence of the pipe alongside it running hot (and being known to run hot, as someone, at some point, put heat tape on it).

Seems the coolant has been expanding and evaporating through the top of the tank, regularly enough that it's started to eat away at the plastic.

I am ashamed I didn't check sooner, shocked that the engine never seized or overheated, and a bit baffled.

Anyone else had anything like this?

I topped it off and it's been driving fine for over a week (and not sluggish at all, poor thing--I can't believe what it's been dealing with) since. I check the level before driving and no change at all, which supports the slow evaporation theory.

It is in the shop today for an oil change and for the dealer to look at that, so I assume I will get some kind of answer. I can do basic dry maintenance (coil pack, spark plugs, filters, etc) but I draw the line at jacking the car up and dealing with fluids.

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Old 02-17-2018, 02:17 AM   #2
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Had the same issue a couple years ago. My expansion tank developed a small hairline crack near the middle seam and slowly leaked fluid. Easy fix. Replaced with a Dorman tank from Amazon for $30. Took about 15 minutes and a quart of extra coolant.
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Old 02-17-2018, 02:36 AM   #3
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I also had the same thing happen to me. It was pretty much the same area with the same shaped mark. I had my mechanic take care of it for me eventually.
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