Windshield Wiper Fluid in Brake Fluid Container


I accidentaly put about an ounce of windshield wiper fluid in the brake fluid container. Is that enough to make any kind of difference in my car?

And yes, I realize I’m an idiot.

Thanks in advance.


yes you need to replace the brake fluid. As the washer fluid mixes in, you are more likely to have corrosion in the braking system. Also boiling point for the fluid will go down. There shouldn’t be a problem in the short term. But sooner it’s changed the better.


Brake fluid, as you know, is critical. It also happens to be very sensitive to moisture. Yes, you do need to get it out. Tell the tech what happened and make sure the entire system is flushed.


You can get away with an ounce of washer fluid in the coolant, gas tank, or even the oil, but NOT in the brake fluid. Have the system flushed.

Your car may appear to brake normally during light use, but in need of heavy use you are in for a surprise.


You are not the only idiot.

Back when I had a '69 Porsche 912 (don’t get me started) I found a plastic hose that seemed to be from the windshield washer loose in the luggage area (front). I hooked it up where it looked like it was supposed to go … and proceded to pump most of the washer reservoir into the gas tank. It took many bottles of alcohol to get the gas to burn smoothly again.


It’s a TIME thing…WHEN did you do this? An hour ago, a day ago, a week ago? Have you driven the car/stepped on the brake?? If this happened TODAY, and you have not stepped on the brake pedal, you should be able to use a turkey baster to remove all the fluid from the master cylinder and replace it with fresh fluid. If you have stepped on the brakes and mixed the fluid, the entire system needs to be drained and flushed with new brake fluid.


If your car is more than a few years old, you probably should change the brake fluid anyway even though most people don’t bother. Now you have a reason to.

Problem is that unlike the other petroleum based fluids in your car, brake fluid mixes well with water. But the boiling point of brake fluid/water mixes is lower than that of dry brake fluid. Unlike brake fluid, gases are compressable. the braking system depends on the stuff in the system not compressing.

I suspect that an ounce of water in the brake fluid won’t do all that much damage for a while. The brake hydraulic system is not designed to circulate fluid so I’d guess it will take a long time for the moisture to migrate to the calipers and/or slave cylinders which are the things that get hot and where moisture could be a really serious problem. But you don’t want to find out the hard way that my guess is wrong.

As someone else suggested, the first step would be to get the fluid currently in the master cylinder out with a turkey baster or something similar. Then refill the cylinder with whatever kind of fluid it specified on the cylinder cap. Unless you’ve been driving the car for weeks since the incident, I’d think that most of the windshield washer fluid is still in the master cylinder.