5W40 vs 15W40?

[BBailey]

This has probably already been asked & answered but I can't find the answer.

I have put Rotella 15W40 in my 04. 5 600 since new. The truck now has 35K on it and I am thinking about switching to Rotella Synthetic 5W40 this winter. Will changing oil weight like that cause any problems. I know that the manual says I can use the 5W40 but will there be problems after having used the 15W40 since new? Once I make the switch I will probably stay with the synthetic.

 

[EErmert]

Well, don't know if it will help, but I also used Dodge, then Rotella 15-40, then at 32. 5k, went to the Mobil syn. 5-40... Have changed oil filter twice, not the oil... just added a new quart to filter and that is that! So, all is well...



Eric '03 3500 SLT SWB QC SRW 6SP HO LIMITED 4X4 WHITE 42. 3K

 

[Alan Reagan]

There shouldn't be a problem. The 5W is the cold start up equivalent viscosity. At temp they are the same.

 

[nickleinonen]

Will changing oil weight like that cause any problems.

none at all...

 

[jwilliams3]

Good stuff! Run it!

 

[RustyJC]

The 5W-40 will provide better flow and easier starting under cold start conditions (the 5W part of the rating) while still providing 40 weight protection under normal operating conditions.



Historically, the concern has been with the large spread between the low and high numbers (i. e. , 40 minus 5, or 35) in the viscosity ratings. The base stocks of true synthetics provide much/most of this improved viscosity index, so that's a benefit. Dino oils, on the other hand, would (to oversimplify slightly) use a 5 weight base stock and then a heavy dose of viscosity improvers (part of the additive package) to provide 40 weight viscosity when hot. The problem was that these viscosity improvers (comprised of long-chain hydrocarbon molecules) were subject to shear and resultant decreased effectiveness over time, so the more that was used (e. g. , the higher the "spread" between cold and hot viscosity), the greater the degradation potential.



Rusty

 

[mberry]

The 5W-40 will provide better flow and easier starting under cold start conditions (the 5W part of the rating) while still providing 40 weight protection under normal operating conditions.



Historically, the concern has been with the large spread between the low and high numbers (i. e. , 40 minus 5, or 35) in the viscosity ratings. The base stocks of true synthetics provide much/most of this improved viscosity index, so that's a benefit. Dino oils, on the other hand, would (to oversimplify slightly) use a 5 weight base stock and then a heavy dose of viscosity improvers (part of the additive package) to provide 40 weight viscosity when hot. The problem was that these viscosity improvers (comprised of long-chain hydrocarbon molecules) were subject to shear and resultant decreased effectiveness over time, so the more that was used (e. g. , the higher the "spread" between cold and hot viscosity), the greater the degradation potential.



Rusty

Rusty,



Is there anything you don't know!? Great post!

 

[BBailey]

Thanks for the help/information folks! I will be making the switch at the next drain down. I'm also hoping it will help with mileage. Every little bit helps at these prices.

 

[jwduke]

It shouldn't make a difference, the synthetic 5W-40 should be good if you tow a lot.

 

[BHolm]

Doubt you will see a milage change. I ran the Mopar oil, then 20k miles on Amsoil 5-30 and now back on Rotella 15-40 because I was feeling cheap after spending nearly $100 to put fuel in the truck :{ Anyway, I still get the same milage. I have also used Rotella 15-40 year around in my '03s. They live outside in northern Minnesota. No starting problems ever. Nothing wrong with going to synthetic though, I was running 10k intervals on the Amsoil. I stick to 5k on the 15-40 Rotella.