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Old 01-13-2013, 09:14 AM
Supercourse Supercourse is offline
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Location: British Columbia, Canada
 
Join Date: Feb 2008
Posts: 3,118
Mein Auto: 2004 X3 2.5i
Quote:
Originally Posted by awdrev View Post
....... when I topped off the expansion tank, I noticed that it continued to leak. I left it alone because the car was hot ......... I kept checking and the amount leaked has significantly reduced but it continues to do so.
I don't think it's necessary in general to have a new cap when replacing an expansion tank.

The rubber seal does dry out but as long as it isn't damaged through over-tightening it can be made flexible again by applying a bit of coolant to it with your finger.

Same with the plastic threads, to make the cap easier to screw on and off.

The plastic cap on an expansion tank looks to me as though it is quite different than the old metal type directly on the radiator which did need replacing routinely.

Not saying it applies here, but it's worth noting that it only takes a cupful or less of coolant mix to bring the float from below the neck up to the Max. position.

Pouring more in doesn't make the float go any higher above Max. but it does mean that it will want to vent out once the car is running.
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