Two years of damp air in your brake fluid
Brake fluid is hygroscopic, which is a technical way of saying it pulls water out of the atmosphere through the reservoir cap and the flexible hoses whether you drive the car or not. Water lowers its boiling point, and fluid past roughly three per cent moisture can vaporise under sustained braking and give you a pedal that goes to the floor. None of that depends on mileage, which is why the major service treats it as a strict two-year job.
Carshalton makes the point rather well. A car used around the village, down North Street and along Nightingale Road and Hackbridge Road, might cover 4,000 miles a year and look barely used, and the same car has to come down Park Hill from Carshalton on the Hill with its brakes holding it the whole way. Two or three years of damp village air in the fluid and one properly warm descent is all it takes to find the limit.
We change the fluid completely rather than topping it up, working from a sealed container in the grade the car calls for, usually DOT 4 or DOT 4 low viscosity, and we test the moisture content before and after so you can see the difference on your report. Where the system needs the ABS pump cycling to clear the old fluid from the unit, we do that too, which is part of why the service takes most of a day.
Spark plugs on petrol engines and the fuel filter on diesels come due at this service as well, if your engine is actually at that point, and everything in the full service is included: oil, oil filter, air filter, cabin filter and the wheels-off inspection with the brake measurements written down. We work out what is genuinely due before quoting, and we tell you what is not. Repairs carry a 3-month workmanship guarantee.

