My 98 Expo uses Dot 3 brake fluid. Is their any benefit in flushing the system with the newer Dot 4 syn? Will Dot 4 affect the seals etc.?

 

rangedog,

I have been using Valvoline SynPower Dot3/Dot4 synthetic brake fluid for over two years in all my vehicles and really like it. It has a higher boiling point and doesn't attract moisture as easily as conventional brake fluid. I tow alot so i like the higher ratings of the synthetic. Down side is that it costs more than conventional Dot 3 brake fluid.

If you don,t tow alot or drive alot in the mountains, and if you periodically flush your brake system then the increased cost of the synthetic may not be worth it to you.

Yes it is compatible with all your seals etc.

Just my $.02

Hope this helps.

 

The only difference between DOT 3 and DOT 4 is a slightly higher boiling point. It's still the same stuff.

DOT 3 is all that Ford recommends and has a plenty high boiling point.

Virtually all glycol-based brake fluid is made by the same company at a plant in Missouri. Buy the cheapest that you can find, because it all came from ther same tank.

 

If you drive in the mountains at or near full gross like I do, It does make a difference. The most important thing is to flush the fluid every two to three years if you live in a humid climate.

Jim

 

I believe that synthetic brake fluid is rated DOT 5. It's silicon and not recommended for anti lock brakes, racing or heavy repeated use of the brakes because it can foam. It is non hydoscopic (doesn't attract water or corode) and wont eat paint. I've used it for years in my 77.

 

OK. For that 5%-10% of the truck buying public, spend the money on DOT 4.

Everyone else, SuperTech DOT 3 is $0.78/pint at Walmart.

 

It is important to clarify the difference between "synthetic" Dot 4 and silicone Dot 5. They are not compatible, while Dot 3 and 4 can be mixed. Dot 5 is mainly intended for collector cars that are not regularly driven.

The "synthetic" term that Valvoline applies to Dot 4 fluid is marketing. ATE, Castrol and others make Dot 4 fluids without using the synthetic term. The chemistry of Dot 3 can be called synthetic in the same way as PAO or ester motor oil.

Jim

 

(insert sarchasm) So THATS why my wheel cylinders keep leaking.

 

I have never used it but I have heard DOT 5 is noticeably "compressible". Any truth to that statement?
edit to add: I thought that all liquids were essentially non-compressible.

 

I think DOT 5 has a much higher boiling point than DOT3 and DOT4. The guy who pulled the instrument trailer for my high school band had DOT 5 in his dually, which regularly towed heavy loads. I don't know if it's compressible or not, but I would think that to gain DOT approval, it must be safe to use. It is not compatible with any other brake fluid (it's silicone) so the system must be completely purged of the old fluid before putting in DOT 5. Other than that, I don't know a lot about DOT 5. I think for what I use my truck for, DOT 3 is good enough.

 

Silicon works like a charm in my Truck and in the motorcyle I used to ride. Liquids are not compressable. To earn the DOT 5 rating it has to have better qualities. It will however foam in anti lock systems or under repeated hard applications I am told.

 

My mechanic agreed to change my brake fluid if I really wanted him to do it. But he recommended that because it still looked pretty good (though a bit dark brown), and had no visible water droplets in the reservoir, that I could simply use a turkey baster to remove all the brake fluid in the reservoir, and replace that a couple of times. He said that would replace most of the fluid, and would be much cheaper than bleeding the system.
I did that, and the fluid now looks fairly clean, brakes work fine. The truck is a 1988 F150 XLT 4x2, 302, AOD, 3.55 axle, trailer tow package.
Any comments as to whether this was a good idea?
Frank.

 

The brake fluid does not really circulate unless you have a leak and keep putting in new fluid. Changing the fluid in the reservoir does not change out the fluid in the lines and wheel cylinders.

The water dissolves in the brake fluid. Brake fluid is a glycol base, like antifreeze. Do you see water droplets in your antifreeze?

 

Nope, I don't see water in my antifreeze, but what you are describing is different from what my mechanic said--he said that the fluid does circulate throughout the brake system, and that changing the fluid in the reservoir a couple of times would be like changing/renewing about 2/3 of the entire fluid in the system, which he said was pretty good.

I don't know which of you is right; however, if it doesn't circulate at all, then why would the fluid in the reservoir get dirty, as it is enclosed/protected from dust, etc., so it should stay as good as when it was added.

I have no clue about mechanics, so I would appreciate any other opinions or information on this topic.

Thanks for the reply.

 

I know it circulates and have for the last 25+ years taken a basting syring at least one to two times a year and suck out the reservoir and replace it with fresh fluid (never low enough as to let air into the lines!) . I have been told not to mix old with new and or mix different brands, but what is done every time fluid is added to top off the reservoir when low? As long as the proper DOT rating is used it's no different than mixing brands of oil as long as your are using the proper rating of it also. Since doing this I have not had to replace or even work on any calipers or brake cylinders, just brake pads when they wear out (last car 240,000miles and still using the original wheel cyl/cal's). I beleive in changing brake fluid like changing motor oil. All you need to do to see brake fluid recirculate is put in the new fresh fluid in the reservior and after using the brakes for a day or so look at it and you will see it has darkened in color after mixing with the fluid still in the lines. I feel by doing this, it never lets the fluid get that bad in condition so as to let the brake system deteriate like things use to do years ago when fluid was only changed when something went wrong. I have very vivide memories of the 70'GTO' having bad wheel cylinders and pulling so hard to one side or another and have yet to have had that happen again since doing this.