Hi all,

Looks like the "debate" is hotting up!

Now remember. I have NEVER said that the oil NEVER needs changing. I just said that changing it at lets say 30k miles is over the top.
So the debate is about WHEN the oil should be changed. I have ARBITARILLY gone with > 100k miles but this is a figure picked from the ether.
Yep, I agree that 250k is nothing special for a modern designed vehicle that is serviced in line with the manufacturers service schedule.
I saw a w140 (I think) with 950k miles for sale not so long ago on eBay!

Now remember we are talking the trans, not the engine, which is a very different situation

So what is the parameter that causes the oil to degrade? and what is the linkage between this and mileage?
I'm sure there must be some oil industry expert out there that will provide the answer and a graph or similar on this.

Now also remember that the filter is designed to remove particles > than x micron which is considered a size that will prevent any sticking of the valves in the valve block. The capacity, and effectiveness of the filter is of course dependent on how much "foreign bodies" are in suspension in the oil. This size will also ensure that bearing surfaces, rollers etc degrade at a rate that is academic.

Finally, what are the modes of failure that have been caused by oil that has exceeded whatever the limit is that was defined in the first part of the question.

Stuart.

PS. It appears that you are all determined to change the trans oil but the differential is a much more arduous application of oil technology. And I don't hear the same desire to change this.

 

The transmission is but through much more use and temperature extremes than the rear diff ever encounters.And yes we service our rear differentials per a maint interval.The diy can be found on benzworld.org w210 diy section.
At 175 f fluid will last a long time,our w210 regularly operate at 185-200f,the trans cooler is the radiator so operating temp is trans temp and 20 degrees temp increase can cut transmission fluid life in half.Never mind all the graphite that floats around and contaminates the sensors located on top of the valve body.Change it early and spare yourself the agony.
ohlord

 

Heat. And, below ~250°F, the oil won't degrade appreciably: but the additives that provide the crucial characteristics do "wear out" with normal use. It's not only a matter of the lubrication qualities of the fluid, but the friction modifiers, detergents, surfactants and temperature modifiers. The heat cycles and their extremes count for more than mileage. Ten minutes of high-temperature operation can count for a decade of normal use.

 

Hi Defiant!

You making the points for me.
Temperature is the key parameter impacting trans fluid life. In "normal" use oil temp is circa 80/90C. No problem.
However at VERY high speed it will rise to 110C dependent upon how long this speed is maintained. However towing will take it to 140C subject to the effectiveness of the oil cooler.

Mileage is not really important. Its duty cycle that is so important.

However, change the oil as often as your budget will allow BUT ensure you use the MB AT fluid otherwise you will be making matters worse than leaving well alone.

Stuart

 

I could not agree more with changing the fluid every 60,000 miles or so. Boxes that don't get this service often fail around the 100,000-130,000 miles. If the fluid and filter are changed they tend to last over twice this distance. I have also been told that if the car reaches 100,000 or so and its not done its best to leave it as the damage is done and the box may fail with new fluid. This is just something I have read

 

How can I drain the torque converter if there is no drain plug? Should I drill and tap one or is there a easier way to drain it?