diff overfilled? 92 500SL leak and smoke
 

Bought car 3mos ago, had diff svc done. Saturday was the hottest day yet this year, and I had the car running a solid 80 on the hwy for a 120 mile trip. On way back, stopped for a drink and smoke was pouring out moderately around the car. Wet under the back, on bottom of gas tank and bottom of both axles, greasy vaporized residue on back bumper.

Does this thing have a relief valve? Overfilled and heat of drivetrain plus ambient temp caused it to erupt? Bad plug? Potential damage done to rear end?

Shop who did the work agreed to look at it. Beyond that, I need to know what to expect and what to demand

I did that one time.I found out when its nice 60s,70s the best time to check diff.You tend to overfill in winter,if its outside.

So most likely excess blowing off, and nothing catastrophic?

I presume if it had leaked out, after 100 miles it would have seized or acted up.

The thickness of the oil could explain a small amount causing a lot of smoke. Takes time to burn off.

These are only my (optimistic) theories....

That was with my Toyota truck.I let it cool and let over foam and fluid drain to right level.No problem after that.Drain your to right level completely clean back end,and drive her short trip till you know no seals are staying popped out.If it still leaks you might need need seals where C.Joints fit into diff.

There are hydraulic valves assemblies for the rear suspension that are located above the diff on the body. Given the sudden and excessive smoke, I'd assume one has ruptured and is leaking hydraulic fluid under high pressure. Be prepared to spend some $$$, those hyd parts are not cheap.

I hope not. I thought self-leveling suspension was an option on these cars? I wasn't aware mine had it. Wouldn't I have noticed a change in ride quality or height? Everything appears normal...

So check this one out.......looks like the previous owner put way too much trans fluid in last time they topped it off. Tech who looked at it said fluid was to the bend of the dipstick - like 3 inches higher than it should have been. No wonder it was shifting hard. The heat and extended hwy driving must have finally pushed it through the relief valve. Hope it hasn't caused any internal problems

Transmission dipstick reading is influenced by temperature of fluid.

As for the differential, I vote for the "leak from nearby" suggestion, as it's hard to imagine how one could overfill a differential.

Oh it was definitely a trans leak....and fluid was too high at op temp at idle, in park. Fluid had run down the housing to the pan, then, apparently, the high-speed cruising sent the fluid on a nice journey back down the cat, to the muffler....ah smoke. Shall drive it gingerly for a few days to make sure all is well. Seems to shift better now.....not as harsh.......which would indicate high fluid. Guess the overflow valve did its job