How often should the brake fluid in your car be changed? How about the differential oil?

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Thanks!

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I’m not a mechanic, but my impression is that brake fluid and differential oil are both more or less permanent these days. You’d replace them if some was lost during a repair.

…If they are replaced I’d expect it would be at one of the super-major intervals like 80,000 miles.

Most cars I’ve had required topping off those 2 as needed, but never an actual change unless something contaminated the fluid. The most maintenance-intensive vehicle I owned in that respect required checking the differential oil every 90k miles.

The owner’s manual or service manual will tell you when to change the gear oil. Brake fluid shouldn’t have to be changed unless it has become wet or otherwise contaminated. Your manual will tell you about that, too.

Thanks, everybody, for your replies. I was asking because I have a used car that did not come with an owner’s manual, and it’s so many years old that I couldn’t find the manual online, either.

Gear oil: If in doubt, change it out. It doesn’t cost much. And consider replacing the oil with synthetic oil.

@kritiper “It doesn’t cost much.” There are large long-lasting indirect costs of disposal of a designer lubricant like those. When it’s something that could outlast the car in I encourage folks to have a substantiated doubt that about the quality before chucking it out.

Like if your differential got damaged in a crash or took a stray bullet, – enough so there are probably all kinds of shredded metal in there – then totally flush that thing out and replace the fluid when replacing whatever got smashed up.