ASSYST indication - intelligent or dumb?

[Nuclear Bob]

I have had my C220 CDI for 2 years and have watched the service indication with interest. I have noticed that I get between 120 and 165 actual miles per 100 miles reduction in the service interval, depending on short or long trips. But I doubt the intelligence of the indication, due to the following:
a) the first 100 mile reduction after a service reset happens after only about 50 miles, b) the final 500 miles of indication happens in exactly 100 mile intervals, c) there is no difference to the type of oil used (synthetic or standard) , neither to the viscosity (10/40 or 0/30), d) occasionally when I have reset after servicing it goes down 100 miles per 100 miles exactly, and upon resetting again after 1000 miles or so, reverts to the longer variable indication (the indication usually changes from an A service to a B service about 3000 or so miles before it is due), e) the indication does not change when adding oil if the level is a bit low.

Also, I have noticed that the mpg indication is always about 15% optimistic, ie. showing 60 mpg against an actual 55. Why? A clue - upon starting up the indication is 40 mpg and reducing, while still stationary ! Surely this should be 0 mpg and rising when the car starts moving?

 

[Rory]

It does take a while for the system to sort itself out after a reset so your comment about the first 50/100 miles doesn't surprise me. ASSYST is supposed to (amongst other things) monitor the oil quality, so I guess the last 500 mile could be that the quality is suffering, or, it could be that the system is really clever and would think that with 500 miles to go you ought to have booked it in for service so it might as well just count down steadily and not muck you about!

As for resetting at 1000 miles - that does seem odd. There are lots of complaints from people with E Class that variable mileage seems to work fine up until first service, but then subsequently it simply counts down mile for mile, but I've never heard that on a C Class before.