Why are diesel oils "heavy duty?"

[dsmith41]

So it looks like it exists but I have no idea where to get it. I don't live in Canada.

I have been toying with the idea of running the 5w-40 Rotella in my Ford Ranger 4.0 SOHC but I think I am leaning towards GC. My manual calls for a 30 weight anyway. I'm thinking the heavier 5w-40 will reduce my fuel economy and I worry about its possible effect on my cat with the ZDDP, even though I believe ZDDP levels have been reduced recently for the SM rating.

 

[travlnman]

I currently use Rotella T Syn 5W40 in my '06 4cyl Ranger, and my wife's '08 Mustang GT. Both have never run smoother! As far as mileage, the difference will be less in your calculations than any other variable, i.e. different brands, different pump calibrations, weather, traffic, driver's mood etc......

 

[dsmith41]

The Rotella T 5w-40 is a group III right?

 

[travlnman]

Somebody else will have to confirm that, I'm not sure. My oil choices have been much simplified. 15w40 goes into the lawn mowers, and 5w40 goes into the cars and trucks. It sounds silly, but it really did smooth out both engines, they were ok to begin with, but there is a difference. Probably because of the higher viscosity, but I'm sure someone will have some insight there too. I have always worked on the assumption that the syn 5w40 was GRP III, if I'm wrong, somebody will tell us.

 

[travlnman]

Upon further research through this forum, I have found a thread on the 2nd or 3rd page in , that has some confirming that the RTS 5w40 is a Group III base.