Approx. mpg on Chevy diesel??

[skobylenski]

So here's the deal, my parents are looking at (actually I'm looking at it for them, since its in New York) a 1994 Chevy 3500, 4x4, crew cab, long box, single rear wheel, 5 speed, 6.5L diesel pickup. What sort of fuel mileage is typical of a truck like this? It has 130,000 miles on it (not that that really matters all that much). I'm not sure of the axle ratio, either.

Now I know, I've put in the good word for another Cummins, so I don't want to hear it about how much Chevy sucks and all that jazz and they've looked at one (a '90 4x2 with the 3 speed), which got about 17mpg, which they were obviously not impressed with since the Tahoe that will get replaced by the next truck gets 18mpg....lol.

Anyway, I just want a ballpark figure that we could expect to see with this greyhound bus of a truck, since I know the axle ratio will make a difference to an extent.

Thanks, Scott