ABC fluid levels

[dldb]

No leaks, no ABC warnings but I do seem to feel pot holes more recently. I've been checking my ABC fluid level, it was low, currently I have it at the bottom 'max level when running' which is fine but when I switch off and wait it goes way above the higher 'max level when off'.

So the system is swallowing up more fluid when running than it is meant to. I assume this is a sign of one or more failed accumulators. I can't get my head round why though - if an accumulator fails then eventually the nitrogen will get bled out resulting in increased fluid capacity in the system, but when switched off there will be less or no compressed nitrogen to push the fluid back. So I would expect the on-off range to be narrower with a failed accumulator, not wider???

Anyone with a normal ABC system - is your fluid range 'max level when on' to 'max level when off'? If so can anyone explain why a failed accumulator increases the range (if indeed it does)?

 

[dldb]

After quite a lot or internet searching (including some wrong info) I think I have found the answer. I think the range of ABC fluid should be exactly as on the dipstick - at the lower 'engine on' mark when idling and at the higher 'off' mark when the engine has been switched off for at least 10 minutes. If the range is greater than this then at least one accumulator diaphragm has split and fluid is entering the nitrogen void behind the diaphragm when the pump is running (so the level drops below the 'on' mark) and leaving it under now unrestrained pressure from the nitrogen when the pump is off, possibly overflowing the tank. As more nitrogen is lost the range increases. As people top up the level when on, the off level rises above the 'off' mark. If you don't top up to the 'off' mark then, when on, the level goes below the 'on' mark. That I think is more dangerous to the system than not topping up to the 'off' mark. But really it needs a new set of accumulators.

I am guessing that, apart from the levels range change, the only sympton, assuming you keep the levels up, is a harsher ride. There could be rubber debris floating around, hopefully the filter will catch it.

 

[alabbasi]

The accumulators are nitrogen filled membranes. If the gas leaks, the level will drop as the fluid fills the space the nitrogen used and you'll feel more bumps. You might or might not see the red abc warning as you go over bumps