expansion tank cap

[MPS]

Is it reasonable to suspect a leak on an expansion tank cap on a 13 year old car? I have a slow coolant leak but it only happens in the winter and wondering for how cheap the part is if its worth trying that before going for a deeper investigation.

[OEM+ DUB]

You would see crystalline deposits with a leaking expansion tank cap - either round the top of the tank or underneath where it vents to in the event of over pressurisation.

If you can't see anything like this then any leak is going to be elsewhere.

Hope this helps.

[MPS]

So they're not really known to fail then?

[ReflexRob]

I have the same slow leak with no sign of cap failure

[pudding]

No they're not known to leak.   If the cap does leak, the expansion tank would show witness marks as already explained.

I'm losing a bit of coolant from the passenger side bulkhead facing corner of the head gasket.   I can see the aforementioned pink crystalline drips on the block.   It's been like that for over 3 years now loses ~100ml over a year, so I have no incentive to pull the head off for such a slow leak.

Have a look around the engine for any leaks, particularly under the crank pulley (main water pump) and the front of the block (electric after run pump), around all the hose connections etc etc.  If the cap isn't leaking, the coolant is being lost somewhere. 

[ReflexRob]

I might have found the answer to our leak courtesy of another member's excellent write up....

http://www.mk5golfgti.co.uk/forum/index.php/topic,95428.60.html

[pudding]

That's a good shout.  I would expect to see some pink coolant on the gearbox though?

[6waysforward]

Mine has needed topping up every few months since I've had it. When I get out of the car when its warm I can smell hot coolant so i will have a look on mine as its been bugging me for ages.