My truck has 20k miles and I want to change over to synthetic oil and a bypass filter. Which Amsoil motor oil is best for a 2006? The Series 3000 5/30 and the Marine 15/40 are both recommended by Amsoil, and I am wondering which is best for my application.

 

15/40 I believe is the best out there

 

I am using Amsoil's Heavy Duty Diesel & Marine 15W-40

 

Yep Heavy Duty Diesel Marine 15W-40 and BMK-11 bypass.

 

Thanks for the info. I was kind of leaning in the direction of the 15/40, but the possibility of more mpg with a lighter 5/30 weight oil (less drag in the engine) was kind of attractive. The other thing that made it hard to choose was that the four ball wear tests between the two oils gave almost identical results.

 

Either oil will work as I've read post from guys in So Cal who use 5w30 year round with out any problems.

 

heavy duty Diesel marine 15W-40 and BMK-11 bypass. i get 20,000 miles out of my oil. oil analysis says i could go longer though!

 

According to Amsoil the HDD 5w-30 is there absolute best diesel oil, and despite being lighter it out preforms their 15w-40 in every aspect. I run the HDD.

 

Crap John! I just bought the 15w40 marine. After I saw my UOA on the 5w40 Rotella syn I think I'm sticking with the heavy weight. I was shooting for the best one this go around though.

Wood

 

I am tempted to try a year on the 15w-40 to look at UOA and MPG differences...

 

I sent my original question to Amsoil's tech help section and just got their answer back. They recommend the HDD 5-30. As long as it really is better I don't mind the fact that it is significantly more expensive than their other diesel rated oils. With oil analysis the cost should be spread over a long enough time that it doesn't amount to that much. If mileage is improved it might even pay for itself with the high cost of diesel.

 

it depends on the climate really, if you live in a hot place mostly year round (south of I-10) then the 5-40 will do fine, if where you live actually has winters and cold months, then the 15-40 is the best all around.

 

Then why does Dodge recommend a 5w-40 in winter climates? And I don't recommend the Amsoil 5w-40 to any 5.9 owner, either the HDD 5w-30 or AME 15w-40.

 

I agree...the 5W40 should be winter and 15W40 summer. I currently run Valvoline 15W40 year round. But, we only get to overnight freezing temps December & January. Not like areas where there is white clumpy stuff on the ground!

Tony

 

As stated, you got it backwards. Lighter oil for colder climates, thicker for warmer.