ua549

None of the US, Japanese or Korean cars I own(ed) came with DOT5 brake fluid. IMO the driving environment in Germany invites more stress on the braking system and MB recommendations are in line with the most stressful use such as hard braking from autobahn speeds. Perhaps other brands don't consider a 5% reduction in braking as serious as others. I doubt if more than a few US, Japanese or Korean cars can stop 100-0 km in less than 100 feet as the typical German car does. I have no idea if there is a braking performance difference between DOT3, DOT4 and DOT5 brake fluids. They wouldn't all exist side by side if one was clearly better than another. This would make for a very an interesting case study!

cetialpha5

Just for clarification, Mercedes uses its own Dot 4+ spec which has a higher boiling point than Dot 4. There's a few Dot 4 fluids out there that have the higher boiling point which you can also use. Don't mix Dot 5 with Dot 5.1. Those are two different fluids. Dot 5 is silicone and can't be mixed with Dot 4, but you can mix Dot 4 with Dot 5.1.

I do kinda agree that every 2 years is sorta overkill but it's a very conservative time frame. I don't think the humidity really matters with the brake system. It's a sealed system although brake fluid does absorb moisture from the heating and cooling of the brake pads.

I think I seem to recall reading that Dot 4 absorbs less moisture than Dot 3, but that once it absorbs moisture, it will boil more easily than Dot 3.

JTK44

Dear UA549:

On the contrary: I have been to Germany and the German drivers are much more serious than American drivers: You do know that it takes many, many months of intense instruction and multiple tests before a person can get a drivers license in Germany. Germans pride themselves on how they drive.

On the Autobahn, drivers are in the right lane except to pass. There is no bumper to bumper at 70 mph like in America. There is no all three lanes being occupied, like at the finish of Ford vs. Ferrari, .with traffic backing up. There is no sudden braking because of tail gating like in America. So no, I do not think that German drivers put more stress on their brakes than cars being driven here.


I do not know if you are correct when you say:

but more importantly even if correct, stopping distance is a function of brakes not brake fluid.




Finally what is the source for:


Certainly, from a products liability point of view, if not changing brake fluid every 2 years led other cars to a 5% reduction in braking distance, every car manufacturer would recommend a brake fluid change every 2 years. If they did not they would be sued.





I suspect just the opposite is true: No cars experience a 5% reduction in braking distance, German cars included, with brake fluid more than 2 years old.

ua549

Brake fluid is an important component of stopping distance. Brake fluid boiling points vary widely between brands of the same type such as DOT4. DOT5 has issues with water accumulating into droplets which can cause brake failure regardless of temperature. As much as we'd like, hydraulic systems are not air tight and absorb moisture via wheel cylinders and reservoirs. If you look at fluid specs they list wet boiling points and dry boiling points with the caveat to use the wet numbers because dry numbers are for pure fluid prior to installation. The worst cases for overheating brakes comes from frequent hard use such as down slope mountain driving. I have driven the autobahn almost every year since 1971. Yes, I have had to brake quickly from 250 kph to 100 kph many times on the autobahn.

Braking loss is highly dependent on lowered boiling points due to moisture. Every vehicle with hydraulic braking is subject to braking loss. DOT4 brake fluid wet boiling points vary by brand from about 300° F to over 500° F. A 5% boiling point loss occurs with a boiling point reduction of 15° F to 25° F.

ygmn

I have not change the brakefluid in my 19 year old truck and she still stops like she was brand new.

Just a way for MB to get $$ for super cautious maintenance.

1guitar

For about $30 you can buy a tool that measures the amount of water in your brake fluid. Unless you live in the Pacific NW your brake fluid will last at least 3-4 years. Again for $30 you can check it yourself or for
$200-$300 you can just let the stealership just change it for you.

V70cat

This looks like a good dot 4? https://www.fcpeuro.com/products/sup...xoCjzsQAvD_BwE

The G Man

Most Mercedes owners do not know how to check their brake fluid’s moisture level, in fact, most of them do not even where the brake fluid reservoir is located. If you are under warranty or CPO, you are require to chnage the brake fluid every 2 years. Its a bit of overkill in my opinion. Once out of warranty, I usually double that time interval.