Accidentally added power steering fluid to brake reservoir but removed as much as I could

So I saw my brake reservoir on MIN, but I thought it was power steering at first. After adding like 1 oz of power steering fluid, I quickly recognized my error.And in less than 2 minutes, I sucked up the entire reservoir with a turkey baster, added fresh brake fluid then repeated that procedure one more time.
I’ve read some bad things on other forums on adding power steering to brake fluid. Hopefully I mitigated any damage. Should I be worried?

If the brake pedal was never depressed with P.S. fluid in the reservoir and the total time is less than 2 minutes, you are probably okay…But I would have the system flushed anyway, just to be sure…You should at least bleed the master cylinder…

I definitely will. This was right all before I had to jam to church service so I’ve drove it a couple of miles after the fact but I guess it will do me no harm to bleed the master cylinder anyways.

You should remove and replace ALL the fluid in the system. Brake fluid is under great pressure which causes a lot of heat, and non-brake-fluids will likely boil which could cause a failure in your ability to stop the car. Never take short-cuts with brakes, steering or tires. Compare the hassle of replacing the fluid with the possible outcomes of brake failure and I think you’ll decide it’s worth the hassle.

+1 on flushing the entire system, simply because of the extreme safety concerns re: the braking system.

That said, given no brake actuation, the odds of contamination are pretty darn low. If it were a (mechanically similar) clutch, I’d probably say “good enough” (but brakes…)

Definitely going to flush the system tomorrow morning.

“Definitely going to flush the system tomorrow morning.”

I don’t think you have to. Brake fluid is a glycol (similar to ethylene glycol or antifreeze) while power steering fluid is an oil (a non-polar fluid).

Like water and oil, the two don’t mix.

Also, power steering fluid has a specific gravity of 0.87, whereas brake fluid has a s.g. of about 1.0, so that power steering fluid floats on top of brake fluid.

Just my two cents.

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It’s a good idea to flush brake fluid every few years anyway; I do about every 3 years.

You have probably reduced the risk of damage to near zero by basting out and refilling the res, twice. If PS fluid is an oil, that’s the source of potential problem, because oil can damage the rubber seals in the brake system. To be extra careful, you could do this: before doing the step-by-step flushing out of brake fluid, detach each brake line from its brake, one at a time, and let the fluid drain out while you keep topping up the res. That will drain out any oil and keep it from getting to the rubber seals.

Some ABS systems might require something beyond or instead of this - someone knows better than I do about that. I have flushed/replaced fluid on my ABS-equipped 1999 Honda Civic a few times without any special attention to the ABS.

@Mechaniker - Thanks for that info. I actually remember reading someone on a forum who poured both fluids in a glass to test. So I tested it out for myself just to see, and it’s as you said. In the picture, the top fluid is obviously PS and the bottom is Brake.

As this is my only car and I’m taking a 250 mile round trip next weekend, it would give me peace of mind just to check around the car anyways (including bleeding the brake system) just as a preventative measure.

@Shanonia- Thanks. I’ll think about doing that. No ABS on this Civic.

I hope you’re not asking because you’ve made that mistake? That thread is 7 years old and no conclusion was ever posted but If I made that mistake I would immediately remove the master cylinder and pour out the contents of the reservoir, pour it half full of brake fluid and stir it around and pour that out and then fill and bleed the master and then bleed the entire system thoroughly. A teaspoon full of oil, transmission fluid, power steering fluid, etc could do $1,000 damage to some cars. Every brake component with internal rubber will swell up like a sponge when it makes contact with petroleum products.

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You didn’t look very carefully… Caliper piston seals, drum brake slave cylinder seals, master cylinder seals, brake hoses, the seals in the ABS module all are in contact with brake fluid and all are under high pressure when the brakes are applied. Those seals are what contains the pressure.

Yes, oil damages the type of rubber used in brake systems just like brake fluid damagesthe type of rubber used in valve cover gaskets.

Brake system rubber is EPDM which is damaged by petroleum oils. Nitrile and silicone rubber used for valve cover gaskets is destroyed by brake fluid, which is a glycol based fluid.

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Nice going . Drag up an old thread , insult women and reply to someone who has not been here in three years.


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The only way a brake system can work is with polymer seals.

Retired, degreed automotive engineer with extensive experience with seals and rubber compounds.

I know the subject intimately and I can provide you with internet links about sealing rubber and can post them if you are inclined to read them.

Quit swearing and insulting other posters or you’ll get yourself banned and not just a single post blocked.


@criminal363_175708 I agreed with the flag. Please stop the cursing, and the insult to women isn’t helping.


@cdaquila Carolyn , you have the power to remove any post that causes problems . So I suggest that all the above starting with the flagged posts and if criminal363 returns ( which I doubt ) then see what he posts.

I think that Criminal363 was just trying to live-up to his screen name.

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