I am not pulling your leg but I have been having a pleasant phenomenon happing with my 2000 ML320 - the gas mileage has been increasing substantially the past 3-4 months. We had been getting around 21 mpg on a trip. Today I just completed an 1116 mile trip where I have averaged 23.7, with as high as 25.8 on one 183 mile leg of highway driving. The driving environment was a range from gravel roads, township roads, county roads, state highways, multilane non-freeway, freeway and city. It was as about a complete mixture as possible. My speeds were at or above the speed limit and I haven't changed my driving habits, and the performance hasn't been affected. I use the cruise control whenever reasonable. The odometer is correct, as I was on a route with mostly known distances and the segment mileages were correct. I have new tires but the same model as the old ones. I used the AC about 50% of the time. The trip was a round-robin trip so altitude changes were not a factor, and didn't vary more than 100 feet anyway. The temperature was 60-75 degrees with rain about 50% of the time, and drove throughout various times of the day from 8 AM through 1 AM. I bought gas at a variety of stations in various towns; Conoco, Holiday, Exxon and Kwik Trip, so the brand of gas shouldn't be a factor. One fill was after about three-fourths tank of gravel roads.

The only changes lately have been with the 320's CEL. About the end of March it came on intermittently and was on about 60% of the time. On this trip it was on about the same amount. I had had the 320 in for a free inspection at a customer appreciation event and the tech's made a note that the airflow sensor needed replacement. The vehicle is due for a "B" service.

I have no complaints about the increased gas mileage, of course, but am curious as to why it is happening. The overall average mpg has been increasing since the vehicle was new but the past 3-4 months it has jumped. Any ideas?

Jim W.

The Mass Air Flow (MAF) sensor is a common issue. When it goes bad, the computer does not know how much fuel to inject (mix with the air). Usually, the result is poor gas mileage. In your case, it sounds like the computer is running your engine a little lean. If this is the case, it can create some engine problems if prolonged, so I would install a new MAF sooner rather than latter.

Can I say that I haven't heard any pinging under load so I hope that is a good sign. I do like this good mileage.

Jim W.

The results of our 510 mile trip: One leg was driving west and northwest, then reversing the course for the return leg. Practically all was freeway with no more than 50 miles of city driving. Our speed was at the posted speed limits or slightly above. Outbound we got 25.1 mpg, the return trip was 26.3 mpg. Very acceptable.

The next day I made the same trip pulling a tandem axle, 1500 lb. trailer, and made 21.4 mpg on the outbound leg against a pretty strong quartering headwind, rain most of the trip with some pretty heavy rain. Again at or slightly above the speed limit. The return leg was with a pretty heavy load on the trailer and the mileage will be much affected. There seemed to be no change in performance compared to past trips and no adverse noises, shifting points, etc.

I hope other M-Class owners can experience the mileage increase.

Jim W.

We get about the same mpg with our 2000 ML320 also, avg 23 on highway up to 27 depending on who's driving & about 19 in town. Been like that for the past year and a half. I have 50K on ours now.

__________________
90 300TE
00 ML320

Mine has gotten around 24 mpg on the hiway since i bought it. It dropped a little when i got the 2nd set of tires (Nokia), but the rain and ice handling are more than worth the minor trade

__________________
...Tracy

'00 ML320 "Casper"
'92 400E "Stella"