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MG MGF Technical - Brake Fluid Replacement

I have just booked my TF135 in for its 2nd year service. The service guy told me that the manufacturer recommends that the brake fluid be changed every 2 years at a cost of about £25. Is this right or are they ripping me off......?

Steve
Steve LE9

Steve,

Brake fluid unless Dot 5.0 absorbs water.

Paul
Paul

No they are correct, the brake fluid is hydroscopic, it absorbs water from the atmosphere and holds it against all the steel parts in the system, rusting them. All brake fluid does this except for silicone fluid (DOT 5) but this has diffrent properties and is not recommended for the F or cars in regular use.
Will Munns

I feel that changing every 2 years is going way over the top - 4 is more reasonable.

Surely you'd have to leave the brake fluid in an open jam jar to get it to absorb enough 'water from the atmosphere'.

Cay brake hydraulics are sealed save for a tiny pin sized breather hole in fluid reservoir cap!

jt
John Thomas

Brake fluid is highly hydroscopic and absorbs water via flexible hoses, the more water content the lower boiling point of fluid, so as the fluid ages so the boiling point is reducing, this is better than having free water.

Will,

Agree with your comment about use of DOT 5.0 Silicone for modern cars esp. ith ABS.

I tried contacting Castrol re SRF fluid (F1 use it) which is a Silicon ester but designed to be Hydroscopic, with regard to the fact that a Silicone DOT 5.0 would not appear to absorb water via flexible Hose but did not receive any comment.

At the moment the only problem I see with older cars and regular use is that Silicone fluid contains air which cannot be bled out giving a more compressable pedal.

The downside may be that if water enters the system via M/c by way of condensation then the water is heavier than Silicone and will eventually end up in lowest part of system the calipers and boil rapidly. A precaution may be to open bleed nipple to remove on a periodic basis.

Paul
Paul

Thanks for the responses, I will go ahead and get it changed then with the service.

Steve
Steve LE9

When I bought my F, I had it tested at a garage befor purchase. They had a gadget with a microscope, in which they tested the boiling point of the brake fluid (that is the water contents).

If your garage has that, they don't need to replace the fluid premptively.

O Sander

Fluid can be checked for moisture and with a dot 4 Dry is approx 230degc and wet 3.5% 155degc. Typical absorbtion rates over 2 years is 3-7%.

The other downside to not changing regularly is the possiblility of brake pipes rusting is increased.

Paul
Paul

This thread was discussed between 26/06/2004 and 28/06/2004

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