Brake fluid level on a borrowed car
June 17, 2019 2:09 PM   Subscribe

I'm storing/borrowing my friend's car, and the brake fluid reservoir is filled almost to the brim. What do I do about this?

I suppose there's two aspects to this question: one part auto help and one part etiquette gut check.

A good friend of mine is recovering from surgery, and I'm storing their car for them while they recover (on-street parking means they'd have to move it every so often, and they can't; I have a parking space). They've said I'm welcome to use it as much as I like during recovery, which should be several weeks.

My friend mentioned that the car had been sitting for a while, and might have some minor issues. Being (only very slightly) more mechanically inclined than my friend, I looked under the hood after I drove it home to check various fluid levels, and saw that the brake fluid reservoir was far over the max line.

Question 1. What would one do about this from a mechanical perspective? I didn't notice any trouble with the brakes on the way home. No idea if water may have gotten in to the system, or if someone just overzealously filled the reservoir some time ago. I haven't asked my friend because I don't want them to worry additionally while they recover.

Question 2. Should I take the car to a shop and just have them flush the brake system? It seems like a reasonable thing to do, if the car hasn't seen maintenance for a while, and something funny's going on with the fluid. Plus, it might be a nice little present in exchange for the use of the car. Or is that taking liberties with a borrowed vehicle?
posted by pykrete jungle to Travel & Transportation (4 answers total) 1 user marked this as a favorite
Best answer: Probably someone in the past topped the fluid level off as it dropped down over the course of wear on a set of brake pads. Then when new pads were put on, the fluid level was pushed back to a higher level.

Honestly I wouldn't worry about it.

If you're truly concerned, take the cap off, use a syringe (or a turkey baster) to remove a little fluid. Make sure you have a ready reservoir; brake fluid will remove paint readily.
posted by notsnot at 2:19 PM on June 17, 2019 [2 favorites]

Make sure you check the level with the engine cold. Checking the level with a hot engine may not be accurate. You are probably worrying too much about it, though, to be honest.

However, a quick word of warning: brake fluid is a very effective paint remover! If you are inclined to remove the cap do not accidentally drip any of the fluid on the car's body. A person I know* once did this and was shocked and stunned at how quickly the vehicle's paint came off wherever the fluid had landed. Don't be like that idiot!

posted by The Deej at 2:22 PM on June 17, 2019 [1 favorite]

Best answer: Car/Engine temp makes zero difference to brake fluid level.

Somebody overfilled the reservoir. The only time it will matter is next time the brake pads are changed and the mechanic pushes the calliper pistons back - there won't be enough room for the extra fluid in the reservoir and it will go WHEEEEEEEE out of the cap and make a mess. Other than that, it matters not one bit.

1: Completely ignore it.

2: Take some paper towel (the non 'fluffy and will lose bits' kind - think good quality blue shop towel, not kitchen towel), open the cap and dip a section in gently and soak up the excess a little at a time to get back to the max level. Make sure you have enough towel or a plastic bag or something to remove the wet towels without any brake fluid dripping.

Either works. Although this is completely a non-issue. Both are equally valid and '2' is more effort than it is likely worth. Personally I'd just make sure the mechanic who changes the brake pads next knows about it. That's all the effort I'd put into it.
posted by Brockles at 2:31 PM on June 17, 2019 [4 favorites]

Response by poster: Thanks for the advice--always glad to hear I'm worrying too much about something. And completely, non-sarcastically happy to hear the "this will destroy the paint and everything it loves" advice, because that's the one thing I remember about brake fluid for no particular reason.
posted by pykrete jungle at 2:37 PM on June 17, 2019 [1 favorite]

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