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.

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 4×4 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,

HO Confused?

I bought a 2004 Dodge 2500 HD 4×4 from a co-worker last summer. He had ordered a new truck, and I was able to buy his old truck for what the dealer offered him for a trade-in (below market).   Anyway, the truck is supposed to have a 5.9L HO Cummins engine.  No one at my local Dodge dealer can tell me if it really is a HO engine.  The HP rating is stamped 305, but the engine doesn’t say anything about HO engine.  I was told that the horsepower rating of the 2004 HO was 325HP.  Dodge couldn’t answer this question.  Hopefully you can.  The engine is great regardless.  With a K&N & Magnaflow exhaust (suggested by your magazine, tuner next.) it is even better.

Jeremy Falcon
Via Email

According to my info archive, the early 2004 model-year Dodge Cummins, when equipped with an automatic was not an HO, and was rated for 305-hp and 555 lb-ft of torque.  The mid model-year 2004.5 HO was bumped up to 325/600.  These later engines got the “HO” designation, which can be found on a valve cover data plate.

Yes, the 305 is still a great engine, and has a lot of potential.  Thanks for writing.

6.5L Diesel Performance Upgrades

I just purchased a 1998 Chevy K2500 equipped with a 6.5L turbo diesel. I really don’t want to do any work inside the engine, so what are the best performance add-ons for this truck? It currently has a straight exhaust and the fuel injection pump’s PMD (Pump Mounted Driver) module has been moved to a remote mount beneath the front bumper to allow it to run cooler. The truck has 175k miles on it, and this is my first diesel truck.

Chris Olmstead
Via Email

Hi Chris, Suggestions for performance improvements sort of depends on what sort of performance increase you’re looking for. Knowing how you use the truck now and how that could change in the future would also be helpful.

Step 1– In general, installing a boost pressure gauge and exhaust temperature gauge should be the first steps in any performance improvement program.

Step 2– The next step involves installing a 3-1/2″ mandrel-bent free-flowing exhaust system.

Step 3– Make sure your engine-driven fan-clutch is engaging whenever the engine coolant temperature reaches 210. You should be able to hear the engine fan “roar” stoplight to stoplight on a hot summer day or anytime you’re towing a heavy trailer up a steep grade.

Step 4– For an otherwise stock engine, I’d consider replacing the stock turbocharger with a Holset HX-35W. This Holset was used on the 1997-2002 Dodge Cummins. Then add an engine programming upgrade that adapts to the new turbo, while adding a bump in fuel rate. This combo will provide for a healthy improvement in performance.

Just don’t forget the boost pressure and exhaust temperature gauges. Once you’ve added performance products, the nut behind the wheel is what helps protect the engine, plus the gauges will help you improve powertrain management for best performance (determine what gear/RPM/Boost/etc.) work best when pulling hills).

Good luck,

Keeping On

Hello Diesel World, I have been a reader for a while now and have recently purchased my first diesel… a 1993 Chevrolet 4×4 with a 6.2L diesel engine. I know that the 6.2L diesel is not in the same league as the new trucks, even though it has quite a few miles on it, the engine still starts very well, runs smooth and the overall truck is still in great shape.

But, I use the truck to commute 5 days a week, so fuel economy is important, but I would also like to improve the truck’s towing performance a bit. Please let me know where to start! Thanks!

Winston Guild
Williams Lake, BC Canada

Hello Winston, Welcome to the Diesel World! 1993 was the last year for GM’s 6.2L diesel engine. Some things to keep in mind when discussing the 6.2 is that it was designed primarily as a fuel economy engine, and having just enough power to do what most people needed to get done. In 1993, the non-turbocharged 6.2L diesel was flywheel-rated at about 155-horsepower and 275 lb-ft of torque.

There’s actually a lot you can do to improve performance, and for not a lot of money. A turbocharger has always been at the top of the list when considering power improvements for the 6.2L, and you can install all of the factory turbo-related components used in the 1992-99 GM 6.5L turbo diesel powered pickups and SUVs. These parts are easy and cheap to find, and they’ll bolt right on without any modifications. With 7-10 psi boost pressure and a minor fuel calibration increase (that you can do yourself), the engine should produce up to approximately 180-horsepower and 360 lb-ft of torque. This is a big percent improvement. If you run at typical freeway speeds, your truck’s fuel economy shouldn’t be affected, but you will see a big improvement in performance.

Incidentally, GM used the very same cylinder block casting for both its 6.2L and 6.5L diesel engines during the 1992-93 model years. The 6.2 just used smaller pistons. So, this means the 1992-93 6.2 can be bored to a 6.5, when the time comes to rebuild the engine. Good luck.Yes, the 305 is still a great engine, and has a lot of potential.  Thanks for writing.


You May Also Like

Improved Filtration Will Make Your Power Stroke Last Longer

Despite its poor reputation, the Ford 6.0L Power Stroke diesel is a marvel of modern manufacturing and engineering technology. They’re tough and with care will last a long time. Issues…

Firepunk Diesel Dirt Drags

Dirt flying, engines revving, and a crowd roaring as you fly across the finish line. What more could you ask for? Firepunk Diesel put on their fourth annual Dirt Drags in September…


Owning a truck can be overwhelming because of the seemingly infinite parts that need maintenance or replacing over time. Instead of making a list of every part in your truck, take a peek at…


As much as some of us hate to admit it, diesel engines do fail. Pushed too far, there is only so much stress an OEM rotating assembly or valvetrain will tolerate. And sometimes even balanced,…