There are synthetic DOT 4 fluids that may not be, but all others aside from DOT 5 are indeed hygroscopic....

DOT 5 is nasty evil stuff... I don't know why it's still on the market. Lousy feel (comressible), incompatible with anything else, etc. All other fluids (including DOT 4) are hygroscopic to some extent, perhaps some are better than others. But you still need to replace it every 2-3 years.

I don't get why some folks whine so much about <$10 in fluid and 1 hour of their time every few years. It's cheaper than an oil change and easier than a coolant flush, and is a serious safety issue compared to most other maintenance items. Go figure.

:blink:

Mercedes owners are tight wads and, they like to whine.:D;)

I love how people are always willing to second guess the work of Mercedes Engineers. Unlike American and Japanese cars the service manuals are written by the Engineers. These same Engineers that torture test these cars all day long on test tracks. While you might be able to "get away" with not maintaining a car correctly your sacrificing something in the process. With the cost of parts being high vs the cost of brake fluid being low there is a high degree of risk with a very minimal financial benefit.

There are two kinds of Mercedes Owners. Those that jump from car to car year after year neglecting the cars. This type of owner is only concerned with the "status" of driving a Mercedes and could care less about the Engineering involved. If you ask them something about their car they could not really answer you. When there is a major repair they do their best to pay the minimum amount and get rid of the car. The other kind of owner is the long term owner who can tell you historical and technical details of their car. They keep them long term and try to keep the car maintained as much as they can afford. When a major repair comes along they may try to save a little on cost but don't mind writing the big check to keep their beloved car on the road a few more years.

What kind of owner are you?

Glad this was bumped.
I was thinking of posting anew anyway.

I recently replaced the brake fluid of my 300D after the 2 yr. mark.
I use Dot 4.

Although relatively clean, it was a bit 'milky'. i.e. not clear especially at the rear passenger side, the farthest from the reservoir.

I cleaned my reservoir also. It was cleaned the last time and there was residue after 2 yrs. this time around.

2-3 yrs. is a good period for replacing the fluid.:)

I follow that schedule on my other cars. Beats replacing calipers.;)

I left the brake fluid on my 300TE for a little over 3 years and it was already black and had some small sediment in it aka rust. Don't leave it.

Get a motive power bleeder and a basic brake bleeder cup and you can do the entire system without even jacking the car up.

ATE Blue is an awesome fluid to use. Makes seeing when to stop bleeding easy with the dramatic color change.

I switched all my Benzes to dot 5 about 4 years ago. No problems at all. No fluid discoloration either. I love the stuff.

When the brake fluid gets to be slightly discolored I change it. I live in Nevada and our dry climate helps with brake fluid life.

re: it isn't that the brakes aren't any good
 

brake fluid has a spec for its boiling point....it also has a spec for its "wet" boiling point... american cars are more often specified to use dot3...whereas german cars use dot 4. there is a higher boiling point achieved in the manufacture of dot 4. the reservoir is able to breathe some, especially above the rubber in the cap. this allows atmospheric to naturally apply to the volume of fluid in the reservoir. the rubber distends as the fluid level drops with pad/shoe wear. the container you get fluid from should be sealed. the fact that you have it open, exposes it. water condenses from a vapor in the air. the fluid draws it or seeks it. it's chemically thirsty for it. the fluid is a polyglycol base. its corrosive and turns more acidic with the presence of h2o. the boiling point decreases . this can be a problem when heat conducts into the fluid. the heat comes from the pads,conducts to the piston, sometimes multiple piston useage in german and other european cars front and rear.!!! engine heat near the lines adds heat to the areas where it can radiate, especially close to the exhaust. the german/euro cars are designed to operate on the roads they have there at speeds different from what we call legal. we (usa) have tried to decrease speeds, increase vehicle lean to make the driver slow down, and we use more drum brakes. since our systems are cooler running (and we want to report inexpensive maint. req.) it is not realized . as we demand harder, faster, cheaper, lighter, we start to need the components like multi pistons, metallic linings, hotter horses, lines closer to heat, then we take it to the ski area or over the pass where brakes are applied more for extended length of the downhill. the air is thinner, the atmosph. psi is less, and thus, the boiling point drops even further. i go by color. if it turns dark i flush it out. usually when renewing linings. oddly enough, american cars sometimes must experience leaks and hydraulic problems before the customer wants help.then its a POS! you can test the acidity with litmus paper. the lube kids at your local shop have these test kits. or the brake shop. you can add reflective insulation to the pipes. put non conductive backing on the pads. be careful of bleed sequence on multipiston apps. note specific instruction about plastic electrical switches, and combi valves that are held during bleed. height sensing valves are used on some cars too. read read read, ask ask ask, then buy tools and become a tech on your own car but please don't run us all over with your catalina before you get a free inspection from just about every shop there is!!!! oh, and throw out all the unnecessary luggage ,grandmas sewing machine, etc etc. hahaha

Warning
 

The technical content of your post is good, but the struggle to read negates value.
http://www.peachparts.com/shopforum/general-feedback/282580-posting-format-readability.html

.

Sorry I didn't read all 11 pages, but a few quick facts you can check for yourself:

DOT 5 (silicone) brake fluid does not absorb water and (almost) never needs flushing. I use in all my ABS cars. DOT 5 is slightly more compressive than new glycol, though better than old glycol (w/ moisture). My pedals are stiff and I notice no difference.

All other brake fluids are glycol based and absorb water. DOT 5.1 is glycol, not silicone. It is the first glycol to meet the higher DOT 5 standards, but must be called 5.1 to not confuse with silicone.

Glycol fluids eat your paint, causing rust below the MC in most cars. My 300D boosters were bare there, though aluminum and didn't rust.

All brake fluids are synthetic - i.e. man-made. Valvoline used that as marketing hype.

When I change oil I also suck the brake fluid reservoir empty too and refil it with fresh fluid.. It will all mix and its easy to do as I use a pump to change oil..

I disagree
 

Here are some of my reasons
http://www.peachparts.com/shopforum/724822-post25.html


.

The last part of your diatribe is completely erroneous. There is absolutely NO WAY your family has put 180K on an old pos Pontiac and never had brake work done involving bleeding the brakes, which would, by its nature, be equivalent to fluid change.

You say in another post the system is sealed otherwise it wouldn't hold pressure and the brakes wouldn't work? By making that statement you show that you have absolutely NO idea how automotive brakes work.

All automobile brakes (ALL cars, from Audi's to Volkswagons) use a brake master cylinder with a fluid reservoir. The reservoir is NOT sealed air tight, it has a breather. This is to allow compensation for fluid expansion/contraction from heat and cold, as well as pad wear which takes greater volumetric capacity and hence fluid level drops. If the cap was sealed air tight, vacuum would be created and suck air into the system.

Mercedes, and many other newer cars, have anti lock brake systems which are very $$$$$$ to replace. The vented reservoir is constantly breathing air in and out, and the brake fluid, being hygroscopic (meaning it absorbs moisture), the fluid slowly becomes contaminated. In addition, fluid in the calipers can run exceedingly hot, and "cooks" the fluid.

So you can just keep driving the car and fail to maintain it, and youll end up replacing a lot of parts long before their time, or you can flush out the old used up contaminated fluid, and get more service out of the vehicle.

Mercedes builds a darn good car, but it is mechanically similar to any other car, and its systems operate the same way as any other car and have the same physical properties.

I'll never understand why many people fight tooth and nail to somehow avoid just flushing the brake system with fresh DOT4/DOT4+ fluid every 2-3 years. I mean c'mon, it's $10 for a liter of top-notch fluid and about 1 hour of work. Even the cheapest oil change is double or triple the cost. Makes no sense to me... just flush the fluid every few years and pay the lousy ten bucks.

:blink: