[Diesel_Dave]

Originally Posted by Night_Sailor

1) That bigger exhaust systems don't do much unless you are at high throttle settings. I don't plan to tow 15,000 lbs or strain my Duramax if I don't have to. These seem like a waste of money.

Agreed. Bigger exhaust is better, but the effect is very small unless you're running near max power.

Originally Posted by Night_Sailor

2) I also researched air filters and found that free flowing air cleaners help, but also let in a lot of dirt, while the factory air filters do a tremendously better job keeping dirt out of these motors. I'll keep my stock air filter

I'd keep the stock filter too. Oak Ridge National Labs did a study with diesel and found the effect of air filter restriction on fuel economy to be quite small. Like the exhaust, less restiction is better, but the effect is quite small.

Originally Posted by Night_Sailor

3) That synthetic lubricants don't have a significant effect either, although I intend to try that.

I found a good benefit to switching to 5W-30 synthetic (5-10%). One thing to keep in mind is that the effect of synthetics will be greater in colder weather and with shorter trips (more cold oil operation)

Originally Posted by Night_Sailor

4) I did find research that fuel additives do improve fuel economy. The best reported was bio-diesel blends. I plan to try that as soon as I can find a good source for this. Next best is a product called Opti-Lube XPD. This is a cetane booster and lubricant. From what I gather the new low sulfer diesel fuel does not have adequate lubricants in it and over the next few years, bio diesel blends will be common. In the mean time I started using Opti-Lube XPD and saw an immediate jump in fuel economy to 17.75 mpg on mostly highway at 62-65 mph, with some city. I was impressed. Tires were stock sizes and non aggressive tread patterns.

I next cut back my speed on the parkway and saw a further improvement. Even using air conditioning, at 55mph, I saw my new best record, 18.82 mpg on 51.4 gallons. I think 19 mpg might be achievable if I keep my speed at 50 mph.

All these were measured with full tanks driven to the warning lights or a bit beyond--53 gallon tanks with typical fills at 47-52 gallons. In the past my typical range was 700-750 miles, 650 in the winter. Now I'm routinely getting 900 miles on a tank, and once 969 miles! (32 miles past the low fuel warning light) I plan to try their oil additive next.

Last trip at 65-70mph yielded 16.81 mpg. I can honestly report a gain of between 6% and 11% improvement due to the additive alone; the rest I attribute entirely to slower driving.

My motor is turning the same rpm/s with less work/fuel needed to maintain these speeds, and it runs much quieter for this reason.

I hope some of you other diesel guys will give this product a try and report your results.

I don't put too much stock in FE claims from fuel additives. That being said, it is somewhat fuel system dependent. Older fuel systems aren't as robust as the newer common rail systems, like mine. I did an A-B-A on Howe's Meaner Power Kleaner and found no difference whatsoever. Recently, I've started using some Schaeffer's Diesel Treat, but my intention is more to keep the fuel system clean than it is to get better FE directly. Keep in mind that even 5-10% gains are tough to reliably see in real world driving because there's som much variation in weather, trafic, etc.

As to biodiesel, I haven't run it in my truck, but I've burned lots of it in an engine lab on the dyno. The energy content is lower, but only about 11% for pure B100. The cetane rating typically is a little higher, so in some rare cases, blends like B5 & B20, have actually been shown to have a very slight FE inprovement (<5%), but even that is fuel system dependent. You may have economic and/or environmental motivations for running biodiesel, but don't expect any mileage improvemnt from it.

In the mean time, good luck and start keeping a detailed fuel log if you haven't already.