McLaren997

When my 4 year maintenance was done by a Porsche dealer it did not indicate they had done a brake fluid flush but they did charge me $40 and change for a litre of brake fluid. That was 8 months ago. I got an ITEQ Brake Fluid Tester Pen from amazon for $12 and it indicated no water in the brake fluid. I have often wondered how often the brake fluid really needs to be flushed, I live in Florida where it's very humid but I still doubt every 2 years is necessary. I'm goin to find out using this tool.

McLaren997

I was wrong, my invoice does indicate a brake fluid flush.

asellus

"When it has too much water" is the answer you're looking for.

Every two years is a good rule of thumb, but exceptions exist that can shorten or lengthen that time considerably.

Tier1Terrier

Can you enlighten on what types of conditions may shorten or lengthen the interval? More interested in the lengthening part, particularly because many owners put low miles on their cars and keep them in a garage. For instance, I'm averaging about 5k miles per year and my car is always in the garage. I live in FL though so perhaps humidity plays a role.

asellus

Environmental humidity is almost exclusively the issue here. Brake fluid is hygroscopic, and brake fluid reservoirs are not sealed units. if you store your car in a low humidity, climate controlled bubble then you could probably get by for quite some time before having issues. I'd say a far, far away second place would be heat. Unsurprisingly, heat breaks down the fluid. Beyond that, maybe seals or the brake lines themselves?

Is 2 years a shorter interval than most people could get away with? Yeah, absolutely. Does it hurt to change it out anyways? Not one bit.

As an aside, the aversion to changing it out every 2 years is one of the more asinine things I see on this forum, what with a set of tires costing as much as a rusty beater.

McLaren997

It's not an aversion to changing it out, it's a desire to understand how much water is absorbed in my humid climate. Maybe I need to do it every year. My guess is very little water is absorbed and the changing the brake fluid every 2 years is actually unnecessary even in my climate. We'll see.

Jack F

Maybe you can test the fluid every 6 months just for fun and see what the reading is. The one variable is if the tester is calibrated and reliable. I for one would want to see the readings more out of curiosity. Thanks.

asellus

This is huge.

The majority of electric testers out there are absolute trash. The single-use test strips are going to be your best bet.

koala

Also, the fluid in the reservoir probably has less humidity in it than fluid closer to the brake calipers.

Even though we're dry AF here in Alberta, I still have it changed every 2 years. This is one item I pay an indy to do - for whatever reason brake fluid flushes are one of the most reasonably priced maintenance items for the amount of work involved. As an aside I truly dislike doing anything brake-related myself.

IXLR8

Why would you think that, considering the reservoir cap is vented.

Anyway, I change the fluid every 4 or less years in my daily driver that sees far more weather than my toys. I have kept some of them as long as 16 years and have never hard a seized caliper. Nothing like regular maintenance; works well in aircraft.

koala

I was admonished for testing at the reservoir by others, and told this is the reason you don't actually test there. I honestly don't know what to think anymore, lol.

asellus

Yeah, and if you're going to the effort of cracking the bleeder at the caliper, you might as well just take the extra ten minutes and bleed it.

IXLR8

Well one way to find out for sure is test the brake fluid coming out of the caliper and compare it to the brake fluid in the reservoir. But then, who cares.

The best thing to do is replace the brake fluid every so many years, in my case even in my daily driver Acura and other cars before it. I change it every 3 or 4 years and I have never had a brake issue....period! On a positive side especially if you drive in the winter with salt covered roads, doing so prevents the bleeder screws from seizing and some others know how easily they snap off. I have to do my girlfriend's car as the brake fluid is original in her 2012 Hyundai. Sure enough it tested >4% but then all I had to look at the color...medium brown instead of a light cooking oil color. No surprise there.

Kitc2246

My local PCA requires racing brake fluid to be changed every six months. Changing the brake fluid is pretty far down the list of expenses for tracking a car. I understand the liability issue for requiring it, but I regularly check the brake fluid for moisture content with a "cheap" Amazon tester and have never registered >1%. I have asked several times why testing the brake fluid for moisture isn't an option. I get two answers: too technical and time consuming and the insurance underwriters won't let us. The NASA tech form does not have a brake fluid type or change date. My two SUVs on the other hand both registered above 2% after three years and had the fluid changed. I understand the fluid boils at the caliper but question the science behind why measuring at the reservoir is wrong. Logic would suggest the vented cap is the primary source of moisture/humidity. If you examine the boiling curves for brake fluid they all start dropping above 2% and even more at 4%. An average driver and vehicle might never boil the brake fluid even at 4% but at that point you should be concerned about corrosion.

For the OP in Florida I would trust the tester and wait until the moisture content was above 2% unless you track or aggressively drive the car then would change at >1%. I bet you easily get more than two years.

The heavy construction and airline industry has been changing fluids based on testing for decades not an arbitrary passage of time. As with car oil analysis it will show the condition of the oil, remaining additive life and more importantly early indication of a part failure.

Jim981CS

I just watched a recent episode of “Two Guys Garage” about fluid types and they stated that the DOT 3 brake fluid is less hydroscopic than the DOT 4 that we use in our 991/981’s and the DOT 5.1 needs to be flushed even more often. They also confirmed that tracking the car requires more frequent flushes. I was not familiar with this difference between the DOT3, 4 and 5.1 and IIRC decades ago with DOT3 fluid brake fluid flushes were not typically done as a scheduled maintenance item.
JIM