Getting Better Mileage From An Older Peterbilt

I would agree with stranger as to making sure the engine is tuned. Probably wouldn't hurt to have the injectors gone thru and rebuild the pump. Get the rail pressure set up a little higher than stock with about a number 12 button in the pump. Also as he mentioned make sure the overhead is run correctly. That is critical and it should be run at least every 50,000 miles or you will beat the copper out of the injectors. With the ulsd fuel try adding some howes or lucas to boost the cetane level. Dragging a belly dump especially on job sites tends to use more fuel than going down the road. One other consideration is how many miles are you actually putting on the rig? Even boosting fuel economy by 2mpg and running 1000 miles a week will only net you a 75.00 savings.Anyway that's my 2 cents worth

 

ever consider a transmision with a deep reduction so you could use a more highway friendly rear gear without loosing th ebottom end?

I know that's pricey but if you want to keep it (and I would) then it's all stuf you will end up doing anyways.I wouldn't get rid of it. The piece of mind "knowing" your truck is priceless. You buy something else and you on't know what you will get.
Pittsburg diesel injection can set up a cummins pump like nobody else. Great thing is that cummins pumps are cheap. You can buy one from them instead of having to pull yours and wait for it. Call them and talk to them, they are the best cummins performance people I know of

 

What about water/meth injection? Quite a popular mod to increase mileage and cool exhaust temps on diesel pickups. I'm about to add that too my duramax. Reasonable cost of about $500.00 and u pick up added hp too! Just a thought!

 

Suggestions here may improve fuel mileage a bit but not much. I ran a similar setup hauling logs and was happy with 4 mpg. Running in a 55mph state and the work you do I would stay with the rear end ratio you have. If you do a lot of running empty a 15 speed would help ( the big jump in top gear was designed for work trucks.)

 

I just read this whole thread an no one mentioned the easiest and first thing i would to get better fuel mileage out of your rig. I would change the gear ratio in the rears and get it more realistic like 3.73 or so would do wonders for the fuel millage and still be able to pull well. The tune up and over head and every thing are givens but the easiest and quickest way to get better fuel millage is go to a taller gear and bring the rpm down on that motor.

 

you don't want to bring the rpm down too much on this engine. Giving it a little more rail pressure will give more power and better economy. The small cam is not designed to run much lower than 1500 rpm. If you try pulling the rpm down and lugging you will start breaking head bolts. For a 55 mph state 4.11 single over 13 and tall 24.5's are a good combo. The tall rubber gives more ground clearence for dirt work and they cap very well. If you are running a lug tread design that also will lower economy by 2 tenths a mile also.

 

That's beacuase he's working of road where he needs that gear

 

howabout an RTO18?

 

Hey I was reading this thread and had some thoughts.

First is that your Small Cam 350 is designed to run from 1700-2100 rpm. It's fuel milage will never be as good as a newer engine. Running it below 1700 rpm can damage it.

Does this truck have a air fan or a solid driven fan? If it's solid driven that will kill your fuel milage.