Check your dipstick
 

I checked the oil in the 81 today and found it was a quart down so I added that much and then headed down the road to my daughters soccer scrimmage about 25 miles away.
About 5 miles out I noticed the oil pressure guage was behaving very erratically; dropping to 1 then slowly climbing back to 3 , repeatedly.
I got a bit concerned and stopped in the next town and opened the hood to find the dipstick was not fully seated in the dip tube by about 1/2" or so.
I pushed it completely in and restarted the motor and thankfully that put an end to the flucuating guage.
Anybody have an explanation for this?

Is your oil over full now?

I found that if you don't get the dip stick fully seated, and have a modest amount of blow-by, which my W123's do :o, then it can puke the dipstick out a ways. Makes one heck of a mess too........ :mad:

twalgamuth - oil level is between the marks on the dipstick
JimmyL - I thought about blowby pushing up the dipstick but this car has little or no blowby.
I think I may not have pushed the dipstick all the way in after adding oil and then checking it.
The dipstick was firmly seated after the ride home.

Don't see how a loose dipstick would effect the gauge. I'd keep a very close eye on the oil pressure to see if it repeats.

I have been.

Mine acted the same way when oil pressure relief valve failed. I installed a used one from another 617 and had no more problems (a new one would have been a 3 week wait from MB).

The FSM also mentions that the valve can come loose, it tells you to reinstall it with a threadlocking compound, which my local dealership service dept. assured me was nothing but loctite.

The valve is easily accessed by dropping the sump pan and then it just unscrews out of the oil pump. I replaced my sump pan at the same time, a new one was only about $30 or so as I recall, from that internet parts store with the german -sounding name in AZ.

Does the 616 also have the valve?

I didn't know that this could happen. Interesting . I'll have to ensure its seated as well as possible each time.

Need to get you to drive my car to see if its got anything going on with it that I've missed.

Have you heard anything about there being the late fall technical GTG like last Nov ? Honestly I have not looked for such a conversation yet but thought I would ask you.