Seven Fluids are the top concern for any Mercedes-Benz 190E. The ones you think of most are probably gasoline and motor oil. Transmission fluid and engine coolant are next and easy to to remember. You might even think of brake fluid as a service item and it certainly is. Extra points for remembering power steering and it’s fluid needs.
But every 190E also has a differential. And every differential is full of fluid.
And that fluid needs changing.
Specifically, the 190E differential is filled with .7 of a liter of 90 weight gear oil. Changing it regularly is an easy and effective way to keep your car going down the road trouble free for many years to come.
The actual process is simple enough, drain the old fluid out, and put the new fluid in, but you will need some different tools than a regular engine oil change demands.
For one thing, the car needs to be level while topping up the differential in order to get the correct amount of fluid in, without over filling. So you will need a level of some kind and two pairs of jack stands or a lift.
You will also need a pump to get the fluid from the container into the diff as the fill plug is not on the top, but the side and it is only accessible from underneath the car. It would be very hard to fill with just a tube and gravity feed.
The other unusual tool needed is a large allen key hex bit, 14mm in size. It is both large and an unusual metric size. I recommend the kind of bit that goes on a ratchet or breaker bar, just because of the force needed to remove the fill and drain plugs.
The Mercedes service manual does say to do this service, first at 7500 miles and then at 15,000 mile intervals. It does seem like a lot, but the fluid is, at this writing, under $10, the process takes less than an hour and it seems to me to be cheap insurance.
I previously had a 1985 190E, bought cheap off of eBay, run ragged, no service history, broken odometer, non-functioning accessories, and I never changed the diff fluid. I have no idea if it had
ever been changed since new.
That is what finally killed the car - the diff broke, in a dramatic and exciting way while crossing oncoming two-lane traffic. (And then I broke tools and bolts trying, unsuccessfully, to get the rear axles off to replace it.) The whole thing ended up going to the breakers.
So yeah, $60 over 100 thousand miles seems cheap insurance to me.