Brake Fluid

I have been unable to find Castrol LMA brake fluid anywhere. I have always used it and now my problem is what to use, Dot 3 or 4? I know they are compatible/comparable. If they are the same, why make two types? I bought some Dot 3 as it is on sale but can exchange it.

Re: brake fluid

I am sure there are lots of threads discussing this but I'll provide a fast and loose explanation. Others will correct and expand as necessary.

DOT-3 and DOT-4 are similar but different types of brake fluid (chemical composition, boiling point, etc.) DOT-3 has been used for decades in American cars and is fully compatible with those old American car brake seals. DOT-4, particularly the LMA (low moisture absorption) formula was used in British cars (among others). American cars had brake systems made of a particular type of rubber that was compatible with DOT-3. British cars used seals made of natural rubber and those seals were only compatible with DOT-4. So, American cars typically used DOT-3 and British cars used DOT-4.

Sometime in the 1970s British braking systems started using different sealing materials which were compatible with both DOT-3 and DOT-4. New hydraulic parts and rebuild kits started using the different sealing material. Since that time, later British cars could use either fluid.

What remains is a risk factor. If you do not know your car's brake history (what has been rebuilt and/or replaced) stick with the DOT-4 fluid. DOT-4 will work with new seals and older ones made of natural rubber. If on the other hand you know that ALL the brake seals and rubber parts are new or have been replaced since the 1980s (seals, flex lines, PDWA, proportioning valve internal bits...) then use either brake fluid. You do not have to use the LMA formulation if you want to stick with DOT-4. Just change your brake fluid regularly which you should be doing anyway.

Re: brake fluid

And if your brake system hasn't been rebuilt since the 1980's (30 to 40 years ago), it's overdue.

Castrol brake fluid is still available, they took the "LMA" off the bottle. It says synthetic now but it is the same identical fluid.
https://www.walmart.com/ip/Castrol-...MI9Y-wo9bu4wIVhlmGCh1RGA8qEAYYASABEgKQgvD_BwE

Thanks all. I've been told that all the dot 4 is the same. I got Preston but haven't opened it yet.

Before switching to DOT5, I used NAPA DOT4 for years. Available in quarts at a very reasonable price.

Edit: according to NAPA site, quarts not shown - only available in gallons.