Make a donation

Author Topic: Wetness on brake fluid reservoir cap  (Read 1351 times)

Offline shail

  • Always Involved
  • ****
  • Thank You
  • -Given: 15
  • -Receive: 32
  • Posts: 435
  • My Ride: http://www.mk5golfgti.co.uk/forum/index.php/topic,99663.msg979899.html#msg979899
Wetness on brake fluid reservoir cap
« 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? 

Offline Octoparrot

  • Won't Shut up.
  • *****
  • Thank You
  • -Given: 8
  • -Receive: 99
  • Posts: 972
    • Email
Re: Wetness on brake fluid reservoir cap
« Reply #1 on: August 03, 2020, 09:23:32 am »
I'd find out if it is brake fluid before assuming. :thinking:

Offline LC5F

  • Just look at my post count
  • ******
  • Thank You
  • -Given: 16
  • -Receive: 79
  • Posts: 1110
Re: Wetness on brake fluid reservoir cap
« Reply #2 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

Offline shail

  • Always Involved
  • ****
  • Thank You
  • -Given: 15
  • -Receive: 32
  • Posts: 435
  • My Ride: http://www.mk5golfgti.co.uk/forum/index.php/topic,99663.msg979899.html#msg979899
Re: Wetness on brake fluid reservoir cap
« Reply #3 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. 

Offline mjmallia

  • Won't Shut up.
  • *****
  • Thank You
  • -Given: 2
  • -Receive: 47
  • Posts: 515
Re: Wetness on brake fluid reservoir cap
« Reply #4 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.
Mike

South Coast

S3 8L ---- Golf Mk4 GT TDI ---- Lupo GTI ----  A4 B6 Sline ---- Golf Mk5 GTI

Offline pudding

  • Global Moderator
  • Just look at my post count
  • *
  • Thank You
  • -Given: 2
  • -Receive: 670
  • Posts: 8229
Re: Wetness on brake fluid reservoir cap
« Reply #5 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?


2007 ED30 | 2009 TDI 140 | 2016 BMW 330D

Offline LC5F

  • Just look at my post count
  • ******
  • Thank You
  • -Given: 16
  • -Receive: 79
  • Posts: 1110
Re: Wetness on brake fluid reservoir cap
« Reply #6 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.