Brake Fluid Change

I know that Porsche recommend changing the brake fluid every 2 years but my car has only done 10,000 miles in the last two years. Do you think I should leave it another year :?:

I believe it's a time thing not a miles thing. From what I understand brake fluid absorbs water/moisture over time which reduces it's ability to do it's job properly, ie it compresses too much... :dont know:

Brake fluid is hygroscopic hence it absorbs moisture once exposed to air regardless of mileage. In fact a regularly used car is probably going to absorb slightly less moisture than one kept in a damp garage. For the the cost of 2 litres of fluid and 1 hour of your time, it is a worthwhile job to do.

Water in liquid form is also incompressible, but the problem is that the presence of water lowers the boiling point of the combined fluid, and brake fluid gets preeeetttty hot. Once it starts to boil you have vapour where liquid used to be, and that is very compressible, so you get lots of pedal travel and not much braking force. And that's a bad day all round really. I think I read somewhere that DOT5 brake fluid is not hygroscopic, so maybe it has a longer service life, but I don't know for sure. H

DOT5 is silicon based thus does not hygroscopic. As a general comment although I am in favour of chaning brake fluid over the last recent years it came down from 3-5 years down to 2 and despite DOT4 been much better than DOT3 etc in terms of hygroscopic abilities. Changing brake fluid is relatively straight forward process but the cost charged does not reflect that. Call me cynical but I will give another analogy unrelated to cars. The normal cholesterol levels have been going down over the last 30 years with no medical evidence that the lowering is to the new levels was required but it means more unti-cholesterol drugs are sold as larger percentage of the population becomes depended on them. So go figure the reasons behind that. Theo

Many years ago I was working on behalf of Automotive Products at Leamington Spa. The meeting was concerned with advancing the sales of brake fluid, which in those days most people retained in their system from the day it was filled at the factory to the day the car went to the scrappy. It was thought to be a jolly good marketing wheeze to promote the idea of regular brake fluid changes in order to increase sales. It is working. Yes it's hygroscopic. No it will do no harm to change the fluid every couple of years. But it is highly unlikely that under normal road use you would ever notice the difference

All the comments about the boiling point reducing because brake fluid absorbs water over time are spot on. Dry boiling point refers to fresh fluid whilst the wet boiling point is with 3% water content. You'll find good info here on the subject http://www.rennsportsystems.com/2c.html One thing to be clear on is Silicon brake fluid which is DOT5 and NOT compatible at all. You must use either a DOT 4 or DOT 5.1. Only performance reason why flushing is important is if you do track days where the brake temperatures go above the wet boiling point due to frequent heavy braking (been there not to be recommended). However, just as importantly, the water content will corrode the brake lines and calipers which is a lot more expensive than a flush every year or 2. For performance, people on the forum favour ATE Blue, Motul RBF600 and Castrol SRF but there are others.