6.0 vs. 8.1 liter Vortec, 2500hd
 

I am currently looking at buying a used 2500hd and trying to decide between a 6.0 or the 8.1 liter. How big of a difference is their in the gas mileage department? This truck will be used on a dairy farm but it will not do extremely heavy hauling. The biggest load will probably either be a 16' bumper pull livestock trailer loaded with 4 full sized cows or a load of scrap metal. This will not be used for hauling everyday and it will not get driven everyday either. Since I will not drive it everyday, gas mileage is not a real big concern but still affects my decision. This truck will be driven empty more than loaded.

Another reason I am considering the 8.1 is for the Allison transmission.

Another concern I have is I have heard these engines like to use oil, especially the 8.1. Why is that?

I am looking at a truck in the 2000 to 2007 range. I do not care for the new body style and couldn't afford it anyways.

What axle ratio would be better, 3.73 or the 4.10? Does it make much of a difference in my situation?

8.1 get terrible mpg, i own a 02 2500hd 6.0 and with no load i get 12mpg. for your situation i think the 6.0 could do everything you need and want and save you some money. personally id rather have a duramax then buy a 8.1. my 6.0 doesnt eat oil, and i have never had any tranny issues and i just broke 140k

Go with the 6.0L if you can. You are likely to get 10 to 12 mpg in a 2500 HD truck. The 8.1 will get about 8 miles per gallon on a good day. That is 20 percent less - which adds up when go go juice runs four bucks a gallon.

Good luck!!

P.S. My Silverado 1500 is downright "economical" by comparison. LOL!