MPG Surprise
 

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.

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

The DOE/EPA fuel economy mileage on the original sticker has the city MPG at 16 and highway at 20. The EPA estimates are usually generous so the mileages we are receiving are very nice. I never expected to get much above 20. At least this is some compensation for the higher fuel prices.

Jim W.

We seem to avg. around 21.9 combined city and Hwy. Driving from Tucson to San Diego....avg speed 80-84 nets about 21. If I hold the speed to 75 the fuel consumption meter bounces between 24 and 27. Higher speed really drop the economy.

Interestingly, going up the mountains the minimum seem to be around 14...still holding 65- 70 but in third gear.

'98 ML320

Trip mileage is approx. 24-25 (approx 70-75mph) mpg and around town approx. 15mpg. Started checking after I had about 2000 miles on the new ML, and has remained constant since then. Speed, mountains, and head wind do affect the mpg. Never has burned any oil with oil changes at about 8000 miles. Dealer used dino oil for the first 2 years, then Mobil 1. I've been using Mobil 1 since then. Org.Dunlop tires at about 32 psi. About 30,000 miles now. 2000 320ML

always averaged over 21 mpg
 

Despite having EGR valve problem code on our ML320 (1998), Since we have owned it(3.5 yrs) it has always averaged 22-23 mpg. On our move up to Iowa from Texas, we averaged 22.5 mpg. I have a heavy foot, wife has light, but the gas consumption always remains constant. I like to cruise at 80-85 on hwy, wife sticks to 65-70.

One thing we always do without fail is use the highest grade fuel. We never use mid or low grade, ever.

Just thought Id share since most ML drivers on this board seem to think that 18-19 is good.

The best I can say for these SUV's is the MPG outstrip the competition. I have a 01 ML430 and towing a 3400 lb. tent trailer have experienced 21-22 MPG on the flats and around 14 MPG through mountain passes. I am completely amazed and enjoy such economy with a V-8 powerplant. :)

-Kevin

Factors that influenced us to buy the M-Class (first a 1998 then a 2000) rather than the competition were the overall size of the vehicle, the mileage rating for its weight, a 5,000 pound towing capacity, the price was either better or competitive with alternatives and the vehicle is made as an SUV, not a converted pickup or a converted car chassis. At the time we bought ours there were no other purpose built SUV's, just conversions. Our current mileage succes has been a very nice surprise, although it looks like we could have gotten better mileage earlier on.

Jim W.