Amsoil 15w 40 vs. 5w 30

[Sixspeed]

I am getting ready to switch my truck over to Amsoil motor oil. The recommended oil is 15w40 but I see that there are alot of you guys out there that use the 5w30. I would like to get some opinons on why one over the other.

 

[Pete Peterson]

OIl

SIXSPEED, run the 15/40. It is what Cummins recommends and its still Amsoil so your good to go. The 5/30 is for people who measure their fuel mileage down to the hundredth of a mile to the gallon. Anyway if your over 10 to 15 thousand miles the 15/40 will keep everbody happy at both Dodge and Cummins... ... ... ... . Pete

 

[EMDDIESEL]

I use the 5W-30 since its listed as a heavier duty oil. Also, better mileage. The dealer will never test for viscosity so i am not worried about that.

 

[SHOOT1SAM]

SixSpeed: Another option is 5w-40 Mobil Delvac-1. The heavier weight during hot weather and the lighter, faster flowing weight during cold weather.

 

[John Berger]

I would go with the 15W-40 for the same reasons Pete mentioned. I'm not necessarily good at following my own advice (see sig) but I also have a pretty good dealer with a top notch service manager. Nice thing is you don't have to listen to me, but I've had pretty good results with the 15W-40. As you can see, the opinions are pretty varied. Either way you won't go wrong.



Update: Sorry about the reference to the signature. Due to circumstances beyond my control I've had to invoke Stealth signature mode

 

[JJW_ND]

5w30 does better!

I have ran both for two 25K mile drain intervals. The 15W40 while still OK to continue use at 25K (no bypass filters here) had higher wear metals and much more change in viscosity. I have ran the 5w30 three summers now. Have had many hard pulls in summer heat (even gets hot in ND) to see if 30w oil is to would stand up. Based on the subsequent oil samples Amsoils 5w30 performed better then the 15W40 in my case.



Under very cold conditions, I was not very inpressed with the 15w40. I think the weight of oil is more important then synthetic quality of oil when it comes to -30 cold starts.



Most automotive manufactures are going to thinner oils. Diesels are just slow to change. Do not be worried about the 30w rating. Atleast in Amsoils case, it out performs their 40w. It also out performs PB2000 oil I ran for awhile.



I worry more about how quick I get oil presure on first startup then the effects of running WOT in 100 degree heat for hours on end... been there done that and seen the results!



jjw

ND