Rodger,
The Scangauge is giving you an instantanious MPG reading and under more ideal conditions you can probably get more. However that is not an MPG Average, and you probably get much worse mileage just getting up to your cruising speed or just getting the engine warmed up.
My MB C300 has an onboard computer that calculates average MPG from the time you start the engine in the morning. When I start out in the morning and pull out of my driveway, I'm averaging about 17 MPG. Within a mile or so I'm up in the 19 MPG range and it continues to improve. Each wait at a stop light drops the average by about 0.1-0.2 average MPG. If I accelearate slowly from the light, I see a drop of about 0.1 average MPG every 200-250 feet while I am still accelerating. Once I get to my cruising speed (regardless of what it may be), I start to gain about 0.1 average MPG every mile or so.
The longer I cruise at a constant speed the more my average MPG goes up, but it increases much slower to where it may take 4-5 miles to increase the average MPG by another 0.1 MPG.
Last week I had to visit 4 ov my companies locations. The trip took all day and when I got home I had traveled 252 miles and averaged 28.5 MPG for the whole day. While my driving speed was only about 53 MPH, I was avaeraging about 72 MPH on the open country roads where the speed limit was 70 MPH. I did have several bursts of speed that hit about 80-82 MPH while passing some slow moving trucks when I was in a leagal passing zone. Those busts of speed would drop my average MPG by about 0.5 MPG and it would take miles of cruising at a set speed to regain that 0.5 MPG back.
I fugure that if I averaged 28.5 MPG for those 252, I would guess that my car was probably getting instantanious readings of 30-32+ MPG for much of the trip to overcome the starting mileage, and frequent stops and accelleration when going through the many small towns that I passed through that day.
I have learned a lot about saving gas just from watching that Average MPG readout and how different driving tactics effect your gas mileage. We all know that rapid accelleration uses more fuel, but when you see how 6 or 7 seconds of full throttle accelleration can really goble up gas that may take 20 miles of sensable cruising to regain the average MPG you wasted.
If you watch you instantanious MPG Scangauge, you can easily see what eats into your gas mileage and what kind of driving maximizes you mileage. It's a great learning tool and I am of the opinion that if you really want to save gas and improve your MPG, forget about mods...Get something like a Scangauge or computer that will give you an instantaneous display and update of your current MPG and it will show you what your driving habits and driving conditions are doing to your gas mileage.
...Rich
