Castrol Motorsport Oils

Castrol motorsport oils and brake fluids cover race and rally cars from the brake pedal to the final drive. The collection holds the Castrol React SRF racing brake fluid for hard, repeated braking, and the Castrol B373 extreme pressure gear oil for limited slip final drives. Both are race specific products drawn from Castrol's long history in motorsport lubrication.

Why Choose Castrol Oil

Castrol has been developing performance lubricants and fluids for motorsport over decades, and these two products carry that expertise into the parts of the car that see the most heat and load. 

The React SRF brake fluid is built to hold up as heat transfers into the fluid under aggressive braking, while the B373 gear oil is formulated to protect a limited slip differential under sustained competition and endurance use.

Both are race tested fluids made to recognised approvals, not road oils pressed into competition. In this collection, you’ll find the two race specific fluids most rally and circuit competitors come to Castrol for. For engine oil, see our oils and lubricants range. 

Castrol React SRF Racing Brake Fluid

React SRF is a high performance DOT 4 racing brake fluid with exceptionally high dry and wet boiling points, which helps prevent vapour lock and fade, reducing the risk of a long pedal when the brakes are at their hottest. The particularly high wet boiling point means it retains its performance better than many alternatives as moisture is absorbed over time, making it more tolerant of longer service intervals.

That makes it well suited to circuit and stage rally use where the brakes rarely get a chance to cool. React SRF has a strong motorsport pedigree at the top levels of the sport, which is a fair guide to how it performs once the brakes are working hard.

Castrol B373 Racing Gear Oil

B373 is a mineral based extreme pressure SAE 90 gear oil, designed for the limited slip final drives fitted to competition cars. Its strength is load carrying and friction control under the shock loads a differential sees on track or stage, which helps maintain consistent limited slip behaviour and protects the gears across a long event. 

It also carries good seal compatibility, so it works with the materials used in motorsport final drives without drying them out. For anyone using a limited slip differential in competition, it’s a straightforward and proven choice.

Frequently Asked Questions

Which Castrol brake fluid should I use for motorsport?

React SRF is the racing fluid in this range. Its high dry boiling point makes it suitable for circuit and rally use where braking is hard and repeated, and it meets DOT 4 requirements.

What is B373 used for?

It is a gear oil for limited slip final drives in competition cars, where its extreme pressure protection and friction control suit the loads a differential sees in racing.

Why does the high wet boiling point of SRF matter?

A high wet boiling point means that SRF keeps a high performance for far longer than other brake fluid, which can mean that the SRF works very well for high performance road / track day cars.