# 5W-30 or 15W-40?



## NBI Lawn (Oct 15, 2007)

I have always run Amsoil in my truck, for all 16,000 miles anyway . My question is what oil weight to run. I was thinking of just running the 15-40 year round but am now wondering if I should run 5-30. Maybe 5-30 would allow for better mileage ? I noticed many of the truck stops around the country sell 15-40 for the big trucks, the Cummins is more like a big truck motor so...

Just noticed that Amsoil offers 5-40 and 10-30 diesel oils http://www.amsoil.com/products/heavytrucks/index.aspx


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## snow7899 (Jan 22, 2005)

I run valvoline premium blue extreme. It is only available in 5W-40 full syn, I have never had any problems with it at all. I don't think the 5w-30 or 10W-30 will be thick enough to use.


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## sno commander (Oct 16, 2007)

i use valvoline 15- 40 from napa, its a blue bottle and cummins indorses it, thats good enough for me. Do use mopar filters?, i hear that you should always use them with the diesels for some reason


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## NBI Lawn (Oct 15, 2007)

sno commander;535376 said:


> Do use mopar filters?, i hear that you should always use them with the diesels for some reason


I wonder why? I run the amsoil dual remote filters


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## Spitz (Feb 28, 2008)

I think 5w30 would be a little too thin for summer but it may be ok for winter.. You'll have to look in your owners manual for the temperature recommendations on that one..


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## exmark1 (Nov 30, 2005)

I run 15 / 40 Shell Rotella in all 3 of our diesel trucks year round. Always have on all of our diesel trucks, never had a problem. They are serviced every 5000 miles.


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## snow7899 (Jan 22, 2005)

There was a lot of talk from Dodge on the filter specs and warranty concerns. They said to use either mopar filters or fleetguard standard or stratapore filters with the cummins. Fleetguard is owned by cummins.


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## tuney443 (Jun 25, 2006)

NBI Lawn;535306 said:


> I have always run Amsoil in my truck, for all 16,000 miles anyway . My question is what oil weight to run. I was thinking of just running the 15-40 year round but am now wondering if I should run 5-30. Maybe 5-30 would allow for better mileage ? I noticed many of the truck stops around the country sell 15-40 for the big trucks, the Cummins is more like a big truck motor so...
> 
> Just noticed that Amsoil offers 5-40 and 10-30 diesel oils http://www.amsoil.com/products/heavytrucks/index.aspx


You're under warranty,so why don't you more importantly follow Cummins recommended oil weight for the ambient temperature where you're running?


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## UglyTruck (Feb 8, 2007)

If you're running full synthetic then dont go by the manf recomendations...the reason for full synthetic is to get away from the short interval oil change & the natural breakdown of petroleum based lubrication. I have seen both sides of the AmSoil debate & I gotta say that I believe in the science.(I'm too chheap to try it out, but I believe it)....I say that you should pose this question to AmSoil & follow their recomendation. 

5-30 is way too light an oil to run if you are running petrol based fluids but the answer may suprise you about the full synthetic. dont expect a 4-5 mpg gain...I would think that 1/2 - 1 mpg would be more realistic. after all it is less drag on all moving parts. 

JMO no need to flame...


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## Unimount219 (Jan 9, 2008)

Most of the Diesels that come into my shop for an oil change run 15-40 Shell, ive never seen them even run anything thinner or thicker, and as far as amsoil goes i like the rotella much better especially if you see some of the stuff that comes outta some peoples cars that we drain, and the leaks syn cause


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## blk90s13 (Sep 1, 2005)

exmark1;536098 said:


> I run 15 / 40 Shell Rotella in all 3 of our diesel trucks year round. Always have on all of our diesel trucks, never had a problem. They are serviced every 5000 miles.


same for me + a bottle of lucas syn oil additive


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## Booman70 (Feb 7, 2007)

Ive run the rotella 15w-40 since my truck was new. Picked up rotella 5w-40 syn. on sale will be going with that on next change. Wouldnt go with 5w-30 to thin the manufacturer calls for dino 15w-40 or syn 5w-40 Id stick with one of those


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## NICHOLS LANDSCA (Sep 15, 2007)

snow7899;536239 said:


> There was a lot of talk from Dodge on the filter specs and warranty concerns. They said to use either mopar filters or fleetguard standard or stratapore filters with the cummins. Fleetguard is owned by cummins.


A manufacturer can't tell you that you have to run their filter. They can tell you to run X or equivilant. If they say you have to use X they have to supply it for FREE.


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## festerw (Sep 25, 2003)

snow7899;536239 said:


> There was a lot of talk from Dodge on the filter specs and warranty concerns. They said to use either mopar filters or fleetguard standard or stratapore filters with the cummins. Fleetguard is owned by cummins.





NICHOLS LANDSCA;544432 said:


> A manufacturer can't tell you that you have to run their filter. They can tell you to run X or equivilant. If they say you have to use X they have to supply it for FREE.


That TSB also included Motorcraft, Purolator and AC Delco filters.


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