SHOULD I SWITCH TO SYNTHETIC LUBES?

I recently purchased a very low mileage 2010 6.7L Dodge Cummins, 2500 4X4, with 3.73 gearing and 6-speed automatic transmission. I use this truck for basic transportation mostly, but occasionally for light towing. I love this truck. I live in Ontario Canada, which is not as cold as the Yukon or Fairbanks, but winter is coming and I am considering changing all of the various lubes used in the truck to synthetic. I am a fan of synthetic oil as I run it in my motorcycle, and all my other gasoline and diesel vehicles, both summer and winter. I’ve always liked the overall benefits of synthetic, such as better lubrication and easier cold weather starting. Now, I have noticed in the relatively short time with my “new” Cummins that my fuel economy (via onboard computer) improves by as much as 3-4 MPG as the engine warms up. I will be changing my engine oil to "Mobil 1, 5W-40 Full Synthetic", and I also plan to change all the other fluids to synthetic as well; including my truck’s transmission ATF and the front and rear differential lube - for improved lubrication, better cold-weather performance and less viscosity drag when cold. Is this a good idea? I know there are arguments pro and con if the cost of synthetic in transmissions and differentials will really be recouped. I believe it will be both long-term financially and certainly cold-weather starting, performance and mileage. Do you recommend synthetic ATF for automatic transmissions and the front and rear differential lubes? For a 9 year old truck, I have to say that the 6.7L Cummins and the 6-speed automatic transmission is a great combination. This truck still looks and drives like a new truck, and I want to keep it that way for another 9 years. Thanks,

Louis Rankin

Sault Ste. Marie, Ontario Canada Thanks for writing. Diesel World did a mileage study a few years ago (happened to be on a Ford) that compared various fuel economy enhancements, their cost, and the time it took for each to break even in its ROI (return on investment). The most cost-effective "modification" turned out to be installing synthetic fluids/lubricants throughout. They cost more, but provide for longer service intervals and we were able to measure the fuel economy improvements and see a reduction in running temperatures. Since the 2001 model year, Dodge, Ford and GM have all used synthetic lube in the rear differential. GM also uses synthetic in the front differential in its 4x4 trucks. It could take 5 gallons to flush and fill the automatic transmission with synthetic ATF. The transfer case only requires a couple of quarts, so synthetic gets the nod there right away. It’s surprising how warm the transfer case can get. This high temperature usually blackens conventional ATF before its recommended service interval. The new high-pressure common-rail diesels all run so cleanly that 7500-mile oil drain intervals have become common place for many years. With a long drain interval, synthetic motor oil makes even more sense, both from a cost of service as well as a fuel economy standpoint. Thanks for reading,