Looking at pulling a 30ft trailer and needing best mpg mods for a 96 6.5..

If your truck is in good working order (engine health, IP, injectors, tires, alignment, etc), it's all in your right foot.

Over 55-ish mph, your MPG will start dropping off pretty sharply while towing anything with any kind of "sail" to it.

Some "upgrades" that can help are:

1. exhaust. 3.5" or better. I don't usually recommend this due to environmental and legal concerns, but removing the catalytic convertor gain see mpg gains. Check your local laws before breaking out the sawsall. Also be aware that if you're traveling state to state (or country) you could be violating their laws also. Johnny law often doesn't care where you're from, just about writing the ticket for where you are. I been hearing California has roadside emissions checks now. Just something to think about. Often old convertors can be clogged with diesel soot, which is the real problem. Most diesel cats are so far downstream they just don't get hot enough to burn off. The 6.X trucks are one of these. A straight through or high flow muffler design can also help.

2. Intake. factory K47 RPO or S&S.

3. PCM. get a heath diesel program for your application. There are others out there (kennedy, Kojo, etc), but I haven't used them so can't recommend or knock them.

4. Proper gearing for your tire size. Larger the tire, the lower the MPG (mostly). Bigger tires effectively raise your ratio. While this sounds good (lower RPM) if you take your engine to far off of it's torque peak, you're not getting the best mpg for the power you are producing. Bigger tires also add weight in the worst possible place, where the engine has to turn it and the weight has the most leverage. Generally, stick to stock sizes for stock gearing.

5. EGT gauge. More for not killing your truck. But if you limit your egt's, you're also limiting the fuel. Unfortunately, you'll also be limiting your speed. Just a necessary evil on a GM 6.x engine.

6. Synthetics. Engine, trans, transfer and axles. May add a mpg or two at best.

7. WMI. MAY give an incremental MPG increase. Don't expect more than 1-2 MPG, no matter what the add hype or your buddy says. Mine adds absolutely NO mpg. Nada, zip, zilch. If it does in any way, it's not measurable. More for EGT control. Keeps the egt's down so you can keep your foot in it longer, so you can keep your speed, which burns more fuel, which brings down mpg, you get the idea. It's essentially "off" when I'm flat running. Don't need it, no benefit to having it spraying. Hill climbing only.

8. Wastegate system. If you're running the stock vacuum wastegate, make sure it's in good shape. Vac pump, lines, actuator, etc. I've got a Turbo master on mine, but a good working vac system can see gains in the MPG area. The turbo master is recommended for use with a heath PCM. The TM runs higher boost in daily/towing conditions, which enables the PCM to add more fuel, which allows better towing/performance, which brings down mpg....etc. Of note, I've run the Heath PCM with the stock system, it didn't like it at all. Over boost conditions. Probably has to do with the Heath PCM being engineered to run a TM. If you're going to run the stock vac system with a heath PCM, MAKE SURE HE KNOWS IT WHEN YOU PLACE YOUR ORDER!

Overall, expect to get somewhere around 8-12 mpg if towing heavy or tall. Maybe a few more if you're got higher than a 4:10 final. 4:10's are better for heavy or tall trailers though, at least from a driving comfort point of view.

My 98 has a new engine (replaced with an Optimizer 6500 this past summer), 4:10 final gears, 4L80E, heath PCM, 4" exhaust, 2.5" crossover, WMI and a raft of other goodies.

Towing this:



34 feet, near 8500 lbs, I get around 10-12 mpg. But I also only get around 13-14 mpg empty. The truck doesn't really notice the trailer back there, if you're talking mpg that is....

Biggest thing I can offer is that if you're into it hard and blowing black smoke with these trucks, you're just wasting fuel and driving egt's through the roof. If you back off to very little black or none, the egt's and ect's come down and your mpg goes up. Unfortunately, that also means your speed comes down also.

Fact of life living with a 6.X engine.

Unless you spend a lot of money on them.

Including the price of the truck parts and labor, I'm into my truck for somewhere around 15-17,000.

Even then, you still have to drive the EGT's instead of the speedo on any serious climbs.

But I can climb vantage, 4th of july or look out pass at legal speeds with (essentially) no egt/ect concerns. Although, I will say look out pass was a butt kicker. Had to drop to 45-50 mph on that one more than one. That is one heck of a hill, not a long climb but quick rise in a short length. Fortunately, there were lots of people ahead of me who couldn't maintain that speed, so I had no issue keeping with the flow of traffic.

Flat running, anything uder 60-65 mph is just cannon fodder. I can pass whenever/whatever I want. MPG goes down sharply as MPH goes up though. I usually set the cruise on 100 kph (about 60 mph) and leave it alone on flat highway running. I just keep and eye on the egt's as the cruise will just hammer the temps when it starts a small climb.

I've gotten more than one odd stare form a few early 'stroke/cummins drivers as I've motored on by.....it's no power house, but it gets it done just fine.

wow thanks for the info!

Thanks, I try.



There's other tips out there, but like I mentioned it's a lot of what everybody already knows; tire pressures, alignment, air filter, engine heath, driving style, etc.....