VW Golf Mk5 1.9TDI - Pressure in the coolant expansion tank

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Thu 9 Feb 2012 12:16
VW Golf Mk5 1.9TDI - Pressure in the coolant expansion tank - cws

We have a Mk5 1.9TDI, and lately the heater doesn't seem to be blowing any hotter that lukewarm (with and without the air-con engaged). Coupled with the this, when you open the coolant expansion tank cap, there a sudden whoosh of pressurised air, and the collant level rises by about 2cm!

Could there be air in the coolant system which is causing both of the above?

The car is running fine and soon gets up to standard 90degC running temp. The coolant also hasn't been changed/emptied in the past 18mths that we've had the car.

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Thu 9 Feb 2012 13:01
VW Golf Mk5 1.9TDI - Pressure in the coolant expansion tank - Peter.N.

Is it ejecting coolant from the filler cap or overflow pipe? If so sounds like head gasket leakage I'm afraid.

Edited by Peter.N. on 09/02/2012 at 13:01

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Thu 9 Feb 2012 13:44
VW Golf Mk5 1.9TDI - Pressure in the coolant expansion tank - cws

No, fluid is not getting out of the tank cap or the overflow pipe. When the tank is un-opened, the fluid level sits at around the minimum mark. When you open the cap, there's a rush of air and the level climbs to just above the max. level.

The car is all running fine and I did an oil change the other day, and the old oil looked fine ie no signs of contamination.

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Thu 9 Feb 2012 14:16
VW Golf Mk5 1.9TDI - Pressure in the coolant expansion tank - jc2

Air lock in heater matrix.

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Thu 9 Feb 2012 14:31
VW Golf Mk5 1.9TDI - Pressure in the coolant expansion tank - cws

Which is exactly what I suspected! However, how do I go about getting rid of the airlock? Unlike our other car, a Passat, the Golf appears to have no bleed holes for the heater matrix.

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Thu 9 Feb 2012 15:06
VW Golf Mk5 1.9TDI - Pressure in the coolant expansion tank - jc2

As long as the pump is working and the heater pipes are connected the right way to the matrix(coolant should return from top)-then set heat to MAX and run engine at 3,500+rpm for about a minute.

Preferably just before thermostat opens(look at gauge)-this should give maximum flow thro' matrix and take any air with it.

Edited by jc2 on 09/02/2012 at 15:10

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Thu 9 Feb 2012 15:42
VW Golf Mk5 1.9TDI - Pressure in the coolant expansion tank - cws

And at the same time have the expansion tank open ie cap off?

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Thu 9 Feb 2012 16:47
VW Golf Mk5 1.9TDI - Pressure in the coolant expansion tank - jc2

Shouldn't matter!

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Sun 2 Sep 2012 03:53
VW Golf Mk5 1.9TDI - Pressure in the coolant expansion tank - b5passat115bhptdi
Hey ive just joined this forum, hope you've solved your problem, from my experiance it should head gasket issues as ive had same problems, an it wasnt mixing with engine oil, but was making pressure in the expansion tank, turned out to be head gasket an cost me £400 in a private garage. It would run fine the after a bit of driving, id get the coolant light come on the dash, when id check coolant level it would be empty till i open the expansion cap an all the coolant would pour out an id have to pour new coolant in. Hope this helps if you havent solved your problems
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Tue 29 Jan 2019 01:03
VW Golf Mk5 1.9TDI - Pressure in the coolant expansion tank - Jamz74

Hi, sorry to bring up an old thread

But I am having the same problem on my Golf 1.9 too

I hope your still here.. Did you manage to fix this at all?

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Wed 30 Jan 2019 02:23
VW Golf Mk5 1.9TDI - Pressure in the coolant expansion tank - edlithgow

Is it ejecting coolant from the filler cap or overflow pipe? If so sounds like head gasket leakage I'm afraid.

Could be, but it could just be air in the system.

(Some?) VW's are apparently notorious for this, and require a vacuum fill. You can buy gadgets for this.

www.youtube.com/watch?v=ADPxM2SC6Mc

But they all seem to require "shop air" i.e. a compressor.

I had a trapped air on issue on my Daihatsu after a drain and fill. If there's a next time I'll try improvising with a big sink-unblocking syringe, or maybe a cheap water-powered venturi pump.

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