I put brake fluid in my power steering fluid

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I put brake fluid in my power steering fluid. I drove it straight to the dealership. They told me not to drive it, but that they couldn't flush it until Monday. Should I take it to a different mechanic or is it okay to sit until MOnday?
Saturday, November 10th, 2012 AT 2:17 AM

1 Reply

Going the opposite way, putting any kind of petroleum product in brake fluid is a huge deal and would likely render a ten-year-old car worth less than the repair bill, especially if it has anti-lock brakes. The issue is the rubber parts. Brake fluid is a glycol product and the seals, o-rings, and flexible hoses are made of a special rubber that is compatible with that. Petroleum-based products will make that rubber swell and become soft and mushy. The first hint of trouble usually is the front brakes start to drag and get so hot they can melt plastic wheel covers. Every year I did a demonstration for my students to show how critical it is to keep brake fluid clean. I put a seal in a beaker of fresh brake fluid, then added one drop of engine oil, power steering fluid, or automatic transmission fluid. After one week we compared the seal to another new one. The contaminated one had grown by about 10 percent and felt soft and gooey. That's what happens to every part in the car that has rubber parts in it.

The problem doesn't come from combining the two fluids. It comes from the petroleum product simply being in the system and in contact with rubber parts. This is so important that experienced mechanics often wash their hands before working on brake hydraulic systems to prevent getting fingerprint grease in the fluid. With your car it's a different story. There are different types of power steering fluid used by different manufacturers but I've never heard of someone causing a serious problem by using the wrong one. That would tend to imply the rubber parts are more forgiving or less susceptible to contamination. With brake hydraulic systems, the ONLY proper repair is to remove every part in the system that has rubber that is in contact with the brake fluid, flush and dry all the steel lines, then replace the parts and fill and bleed the system. I've been a suspension and alignment specialist for a long time and I don't recall anyone ever getting that excited with power steering hydraulic systems. Therefore, unless someone else can give a better reason to panic, I would suggest it's okay to wait until Monday if you have to but it would probably be better if another shop could handle it sooner. With brake systems the damage would have already been done and it wouldn't matter if the problem was addressed in five minutes or five weeks.

If you still run into a steering problem later, the repairs are not going to be nearly as expensive as replacing all the brake parts. My guess is any steering problem that might result from this would show up right away, not days or months after the fluid is flushed. You have to consider how much brake fluid you added too. Was it a tablespoon? Half a can? Brake fluid doesn't have the lubricating properties that power steering hydraulic oil has, but that would only be an issue if the entire system was filled with only brake fluid. Also, why did you need to add any fluid? If there is a leak already, there is some part that needs to be replaced so if that gets worse in the future, you really can't blame that on the brake fluid.

The parts involved are the power steering pump, the steering gear, the high-pressure hose, and the return hose. Any one of them can fail at any time, even without the fluid being contaminated.
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Saturday, November 10th, 2012 AT 4:24 AM

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