I am getting ready to R&R the brake fluid in my 1977 300D (I do this once a year as MB recommends and so far never replaced any brake component except pads). I am considering using synthetic brake fluid instead of non-synthetic because the synthetic does not absorb moisture as readily and should extend the time between brake fluid changes (also less chance of vapor lock and higher boiling temp.). Any comments/suggestions/observations on using synthetic brake fluid instead of non-synthetic brake fluid?

Tom

Why would you want to change the type of brake fluid after 24 years when you never had a problem with the type you've been using. Does'nt make a bit of sense to me.

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

I went for that one in the early eighties. It is not a good idea. True, the DOT-5 stuff doesn't absorb moisture. But the moisture is still there...usually in concentrated little drops that start to eat away at the metal lines from the inside. Nevermind the goofy pedal-feel you get with it. Learn from the mistakes of others...just don't use that stuff. The DOT-4 fluid is more than enough.
Regards,
Randy D.

W.R.,

Are you talking about Silicone Fluid? That stuff has lost popularity, and I/m sure it is because of the reasons you stated. There is now partially synthetic available that will mix with regular brake fluid. I used this stuff in the clutch system on my Vette because the line including the rubber part, goes right by the catalytic converter and everything gets fried. Isn't GM engineering impressive?

If the fluid is being changed once a year AND you're not road racing the car, plain old brake fluid will serve well.

Have a great day,

Hi Larry,
When Tom said "won't absorb moisture" in his post, I figured he was talking about silicone fluid. So yes...DOT-5 is silicone fluid. The partial sythetic stuff (ATe Super Blue?) is fine and it's still called DOT-4. The silicone stuff is best suited for military applications where the vehicles may sit for years at a time. You know, the secret hidden transports and tanks all over the world...stuff like that.
Regards,
Randy D.

Thanks for the info. I see that I should have been more specific about the brake fluid I am considering changing to. I am looking at Valvoline SynPower Dot 3 & 4 spec with synthetic formulation. Currently, I use Pentosin Super Dot 4 but my supply is almost gone. Hence, the inquiry/question about synthetic (Valvoline) versus non-synthetic (Pentosin) brake fluids. Also, the Valvoline brake fluid costs about 40% less ($5 vs. $8.25) than Pentosin not including S&H to have the Pentosin sent to me. Additionally, if the Valvoline is superior to Pentosin regarding moisture absorbtion then I would change despite the fact that the Pentosin has worked for me for many years. I am always looking for improved products to use as technology/research provides upgrades - provided the new product is proven to be better and not just hype.

I do understand that the Dot 4 synthetic brake fluids do absorb moisture, but at a lower rate which should extend the period when the fluid needs to be changed (up to perhaps 2 years?). Am I right or wrong?

I also change my brake fluid when the relative humidity is low - like after a cold front comes through and the RH is about 25% or less. In Texas, that means the best time to change the brake fluid is just around the corner.

I did not even consider Dot 5 silicone based brake fluid. I have known about the problems with this product for some time - but thanks for reinforcing my knowledge/position as it has been a number of years since I last looked at Dot 5 silicone based brake fluid. However, Dot 5 does have it's advantages but I do not believe my needs requires the use of Dot 5.

Tom

Tom,

I doubt that you'll have a problem with moisture absorption using any good DOT 4 brake fluid if you change it out every year or two. The exception would be if you ran the car on the track. Most tracks and clubs demand you have the fluid changed within the last 6 months to run on the track. The brake temps on the track can get much higher than anything MOST of us see on the street so any moisture would be more likely to be heated to its saturation temp. That's the other problem with water in the lines, if it boils you have steam and a compressible fluid.


HTH, someguy