Synthetic Oil--Is it worth the extra cost?

I have a 2007 Dodge 2500HD with a 5.9 Liter Cummins Diesel engine with 18,500 miles on it. I have been using Shell Rotella T HD 15W-30 motor oil in it ever since its first oil change at intervals of about 4500 miles. I also change the filter with oil change. This summer we plan to pull our 5th wheel camper (approx. 12,300 lbs.) from Illinois to Oregon. I’m wondering if I should switch to a synthetic oil for better engine protection or if there isn’t enough difference to justify the higher price of synthetic oil. Anyone have an opinion on this topic?

If you are still under warranty, you cannot extend the oil change interval past the Dodge interval in your owner’s manual, whatever that is. Synthetic oil provides some additional protection against heat issues. That said, my father in law hauls a trailer similar to yours with a Ford diesel engine, and uses the conventional Rotella with good success. He has seen no reason to change and continues to comply with the Ford oil change intervals.

I Use Synthetic Because It Gets So Cold Where I Live.

The Car Manufacturer recommends it for that use. Also, synthetic used to cost 3-4 times more than dinosaur oil. Now it’s about twice and looks like it’s heading lower and dino is heading higher.

What does your Owner’s Manual say about it?

What does Cummins Diesel say? That would be good to know. I’d give them a call, too.


Dodge and Cummins recommend changing the oil every 7500 miles under normal conditions and every 3750 under severe conditions. I’m assuming pulling our 5th wheel to the west coast would be considered severe since we will be crossing the Rockies and the Cascades. The truck is still under warranty so I will be changing the oil according to their specs which means an oil change once we get to Portland. I’m interested to know if synthetic oil is really that much better than dino oil as far as engine protection is concerned. My tendency is to stay with the Rotella T unless its quality is really that much different from synthetic. I suspect that the added cost doesn’t compensate for the quality difference given the oil change intervals that I’m using. Thanks for your input.

I Was Just Wondering If Dodge And Cummins Had Anything To Say About Synthetic VS. Conventional, And Whether They Had A Recommendation.

Like I say, my car’s manual doesn’t recommend one over the other except in extreme cold, then they say to go with synthetic.

I don’t think you can go wrong with your Shell and a severe interval.


Never use less that what the manufacturer recommends. Never change less often than the manufacturer recommends for your conditions. If the manufacturer recommends longer changes, go for it. If not don’t.

You noticed I did not mention synthetic. That is because it is covered above. Don’t expect synthetic to suddenly change the conditions in that engine to allow for longer changes if the manufacturer has not tested and approved it for that kind of use.

Most truckers I’ve met swear by Rotella-T. It’s probably about the best conventional oil you can find. I do think that full-synthetic (like Mobil-1) will protect your engine better in extremes. (hot or cold)

Yes, under the circumstances you describe, if you are willing to spend a teeny-tiny bit more for oil, in comparison to the money you have in that vehicle, switch to synthetic if the manufacturer does not state it is a bad idea, which is not likely.

Compared to cost of good vehicles, the extra cost of synthetic is trivial. And, remember, there is a reason race cars use synthetics.

Do adhere to the change requirements stated by the manufacturer.

Some people really whine about the extra cost of synthetic. You’d swear the few dollars difference every 3500 miles is bankrupting them. Take a calculator and figure the difference for 30 oil changes. It is trivia compared to what you have in that vehicle.

And, do not feel as if you must apologize to anyone. It is your vehicle, and you know why you want to use it. Period, end of discussion.