MK5 Golf GTI

All Things Mk5 => Mk5 General Area => Topic started by: shail on August 02, 2020, 10:58:18 pm

Title: Wetness on brake fluid reservoir cap
Post by: shail on August 02, 2020, 10:58:18 pm
Whilst under the bonnet replacing my bonnet cable I noticed that the TOP of the brake fluid reservoir cap was a little wet.  Nothing major, but wet in top of the cap. I can only assume it's brake fluid, so want to sort it out asap.

Are there any replaceable o-ring in the cap?  I'm not sure how the cap is out together - but it appears to be a 2 piece cap - one bit which has the thread and the other bit fitted through the top of the cap for the sensor.

Any pointers? 
Title: Re: Wetness on brake fluid reservoir cap
Post by: Octoparrot on August 03, 2020, 09:23:32 am
I'd find out if it is brake fluid before assuming. :thinking:
Title: Re: Wetness on brake fluid reservoir cap
Post by: LC5F on August 03, 2020, 10:26:49 pm
The cap should not be an air tight seal

Any recent brake work done?
could just be pads replaced and the fluid got pushed through breather.

give it a clean, brake cleaner is best and just monitor
Title: Re: Wetness on brake fluid reservoir cap
Post by: shail on August 04, 2020, 07:04:36 am
I've sprayed it with cleaner now.  I'll check it in the week to see if it comes back. It was very minor, so may take a while to reappear. 

Not had any brake work done recently. 
Title: Re: Wetness on brake fluid reservoir cap
Post by: mjmallia on August 04, 2020, 09:00:06 am
The cap should not be an air tight seal

It should be an air tight seal the cap, as brake fluid is hygroscopic.
Title: Re: Wetness on brake fluid reservoir cap
Post by: pudding on August 08, 2020, 01:07:27 pm
Maybe it was a bit full to begin with and this heat has expanded the fluid a bit?
Title: Re: Wetness on brake fluid reservoir cap
Post by: LC5F on August 08, 2020, 01:30:38 pm
The cap should not be an air tight seal

It should be an air tight seal the cap, as brake fluid is hygroscopic.

No - I agree that most brake fluids are hygroscopic, but if it was an air tight system you wouldn't need to change you brake fluid every 2 years, this is No.1 location where the moisture gets into the fluid.
Plus the fluid needs free air to flow in and out of the master cylinder, any resistance to fluid flow could be disastrous in an emergency.