[tirwin]

Mods, please to move this another forum if appropriate. I'm posting here because of the sheer expertise in this forum and my question is really about the technical differences in different brake fluids.

I'm prepping to do my first brake job on my MB E350. I started doing research and was surprised to discover the manual has no brake fluid spec listed -- it just says to check with a MB service center. I looked at the brake reservoir cap at it says "use only DOT4+".

My question is what the heck is DOT4+?

Google isn't terribly useful. It mostly sends to me links to buy Mercedes-Benz branded brake fluid.

There is a MB tech spec that says the only approved product is their brake fluid. I cannot find anything that states the technical specifications for "DOT4+" from MB.

Some people on the interwebz say that DOT4+ just means it exceeds the DOT4 spec. Others say that this is special brake fluid that has low viscosity required for MB ABS systems. Still others say the viscosity only matters if you're driving in -40ºF conditions.

I called my local MB dealer this morning and they said any DOT4 compliant brake fluid is fine, but they didn't sound super confident. In fact, the guy questioned whether I was reading the cap correctly because he had never heard of DOT4+ either.

My original plan was to use the same ATE Type 200 DOT4 I use in the 911 since it exceeds the DOT4 spec. Should I go for DOT5.1? Is it ok to mix different glycol-based brake fluids? What do you guys think? Is this marketing hype or do I go buy the extra special MB branded stuff? It's $24/liter so it's not going to break the bank or anything. It certainly is the safe bet, but this just seems kinda stupid and gimmicky. Is there real science/engineering behind this?