Kevdog,

In your owner's manual you should find a specification of how many gallons are left when the reserve light comes on. I have owned a '98 and an '00 ML320. For both the number of gallons left is specified as 3 gallons of usable fuel.

How far you can go on the 3 gallons is predicated by driving conditions, your driving style, vehicle condition, etc. A trip computer can take into account a certain amount of this and will calculate a close estimate of the number of miles left for the gas you have left.

With freeway driving I have traveled close to 100 miles from the time the reserve light came on. I don't believe the reserve light sensor is coming on at exactly 3 gallons of course, but at least it is erroring in my favor. Generally when the light comes on I estimate the miles left by using the average MPG I get. Then I will factor in what kind of driving I am doing; freeway, city, etc. and estimate miles left. Of course I could simply switch the computer over to miles left but I never think of that.

Lest one thinks I run the tank to reserve levels all the time, I have done it mainly when traveling to our neighboring state to the west where gas varies from 16 to 35 cents per gallon cheaper than our state.

Jim W.