My 1999 MB E320 sedan, which I have had for 10 years, gets around 21 to 22 MPG on the highway. I have read that the average MPG I should expect is around 27. I use cruise control for most of my highway driving, change my oil (Mobil 1 5W40) and filters every 7,000 miles, and use the recommended octane gasoline.

Can anyone tell me if 21/22MPG is correct, of if I should expect higher mileage. If higher, how can I increase the mileage? I live in the Washinton D.C. area.

 

my 99 sedan gets 20 city, 29 highway

you'll need to determine what needs improvement, maintenance check,
replacement, etc. we can't tell you what is causing the problem. the car
operates as a system and the contributing cause(s) can be anything from poorly
inflated tires, fuel filter, poorly gapped spark plugs, fouled injectors, or any host
of issues.

so it isn't as if it's just limited to gas, changing oil, and air filter. an in depth
review of sensor read outs may be helpful as well (e.g. emissions)

 

Raymond, thank you.

 

shouldn't you be using 0W40?

 

illest, I was told by my local MB dealer that I should be using Mobil 1 5W40. I also read on some web pages that I should use 0-40.

 

seems a bit low. its not the oil though. how is it running? Tires and tire pressure ok?

 

Seems pretty low. I have a 98 wagon with 140K and I get 18-20 around town and 28-30 on highway.

If you haven't replaced the MAF in the last 50K miles I would start there. Not only does it cause the engine to run rich it will eventually damage the catalytic convertors. $$$

Another thing often not considered is the alignment. Rapid tire wear may not be obvious but the lower gas mileage is. I would recommend a 4 wheel alignment at the dealer. Very few Indies have the right equipment.

 

Richard, what is MAF? The tires and aligment are very good and I keep the tire pressure at the reommended settings. I have around 144,500 miles on the car and had to replace one of the catalytic convertors about two years ago. The other one is still on it and I have had no other problems with the car. The car performs very well and when needed takes off like a rabbit at any speed.

 

MAF stands for Mass Air Flow. It is a sensor that sits just downstream from the air filter housing. Scanning with a OBD scanner usually produces trouble codes such as P0170 and P0173 but no CEL. A faulty MAF has the least effect on acceleration since that's when the engine is calling for extra fuel. Part of it's purpose is to trim the fuel mixture during idle and slow speed driving.

If your gas mileage has been like this for ten years then maybe something else is going on.

 

Richard, thank you. I'll have my mechanic run a diagnostic test to see what pops up.