Quentin Willson's guide to Topping Up Your Brake Fluid
Brake fluid should never need topping up between changes. The level in the reservoir will drop as the brakes wear but will return to the upper level when the brakes are serviced. If your brake fluid goes below the minimum level in the reservoir or needs topping up regularly you could have a serious and potentially dangerous brake problem so take the car to a specialist. If the brake dashboard warning light comes on while you’re driving, this needs immediate investigation. It’s worth checking the level every week. Open the bonnet and look for a small white plastic reservoir, (metal on older cars) usually near the back of the engine. You should be able to see the fluid level through the plastic and visually check that it’s not low using guide marks on the side.
If the fluid has fallen below the minimum guide mark you’ll need to top up and get the braking system checked out at the earliest opportunity. You may have a serious leak or your brakes may have worn to the point where expensive damage could be caused, even though they feel like they are working properly. Most brake reservoirs have the brake fluid specification written on the side or on a label. It’s vital to use only the correct fluid for your car and if you’re not sure, look in the handbook or use the Castrol recommendation tool on the website.
To top up, get a clean rag and wipe round the reservoir top before you unscrew it to make sure nothing can drop in and contaminate the fluid, unscrew it carefully and then slowly add fluid up to the guide level mark on the resevoir side. Be very careful you don’t spill any as its corrosive and can strip away paint. Make sure you wash off any spillages as quickly as possible after replacing the reservoir cap and check that you’ve screwed the reservoir cap firmly back on.