Would appreciate some thoughts on types of brake fluid for a system flush.
I am thinking of switching to a DOT 3 as it will not absorb moisture like the DOT 4. If this is a really bad idea, would be interested as to why.
Thanks.

 

Rather than listen to Internet advice why not buy an inexpensive brake fluid moisture gauge ? Then you will know how much, if any, moisture is being absorbed into your brake system.

I use the DOT 4.0 brake fluid, the best I can find. Two years later it has the same zero moisture content as it did when new. And I live in an area that is very humid 6 months of the year with the being driven daily, about 15,000 miles a year.

the DOT 4 is a substantial upgrade over the DOT 3’s in boiling point protection. That is the specification that I want when going down a mountain pass and have to ride the brakes continuously…..

Z

 

DOT 3 and DOT 4 both absorb water, albeit that DOT 3 is has slight lower absorption rates. DOT 4 is better in every other way which is why it is now the standard for glycol brake system.

Richard

 

I wouldn't do it. DOT 4 has higher boiling point than DOT3 (wet or dry).

But if you did, I don't think its going to hurt anything - but you should still change the fluid regularly.

FWIW I use Bosch ESI6-32N Brake Fluid - its a low viscosity DOT 4 meeting ISO 4925 Class 6.

HTH, Dave

 

Thanks for the advice everyone. I have tested the moisture content, and it does show zero moisture content. However, i have learned that the moisture settles into the calipers and can thus give a false read while doing damage.
My other vehicles have an interesting setup which inspired this. Their reservoir doubles as a specific gravity measure and has actually indicated in the past when the moisture content was too high. All reservoirs on modern cars are open to the atmosphere as we got away from the membrane gasket cap of years ago. Progress...

The other cars, and Toyota is also similar in this regard, have specified their own version of DOT 3 which is actually quite good in terms of corrosion resistance additives and less hydroscopic than the general market products. These OEMs even go as far as to recommend flushing the system if a different DOT 3 is used.

What i will probably do is simply purchase the Toyota DOT 4 as they have engineered it to their own higher standards.

As for braking in such situations as downhill and performance driving, i have always been easy on brakes and prefer to use the engine when any resistance to gravity is sustained for more than ten seconds.

Two years ago helped a friend rebuild the calipers on one of these cars. The rust mess in them required replacing the rears. He flushed his fluid every two years, and the previous owner had it done by the dealer on schedule.

 

You can always crack open the bleeder screw and get some fluid out for testing if you are worried about moisture in the caliper brake fluid.

PS: I’ve been there with nasty calipers.

I’ve restored a few sets of calipers on 1960’s era Shelby Mustangs. Often the calipers were 90% full of a substance that resembled very thick peanut butter, with just a small passageway for liquid brake fluid to travel to the pistons. It’s a
miracle that the brakes worked, and they worked quite well.

 

Jaguar has recommended BRAKE FLUID REPLACEMENT every 2 years.
When I worked at the dealer, we had to fill out the scheduled maintenance record sheet for every service. (no record sheet, no compensation)
See the asterisk for brake fluid on the top line.
I filled out HUNDREDS of these service sheets.

 

of course, I always let the engine have it’s braking effect, as much as it can do in those long downhills.

but engine braking will only provide you so much. Effective engine braking is done in the lower gears, and as such has its limits . We don’t want to be engine braking at 8,000 rpm do we ?

The point being, buy the best brake fluid you can find with the highest boil point. Those specifications are generally published, often on the label.

DOT 5.1 is often the best in that department, but not always. It pays to compare.
(note: 5.0 and 5.1 are not the same , DOT 5.1 is in the same “family” as the DOT 3 and DOT 4)

Z

 

You'd be surprised how many cars come in where the owner swears a dealership has been doing a particular maintenance function regularly, and they have receipts to prove it. Yet, upon further examination, the procedure hadn't been done in years. I trust most dealerships as far as I can spit.