ViperQA1 said:I'm not seeing any mileage improvements with AMSOIL synth 15W-40.
betterthanstock said:To see an improvement, use thinner oil 5w-40 or 5w-30. My 03 manual shows 5w-40 synthetic as the preferred oil.
Cummins has a report that shows 5w-30 as being actually a little thicker than 15w40 when hot ( due to the flatter decrease of viscosity of synthetics).
So you will gain at low temperatures, and lose mileage at very high temperatures, when mineral oil becomes water-thin.
I still like the extra protection of synthetics when shutting down a hot turbo, and most of my trips are under 20 miles, so I benefit from less heavy oil during the first 10-15 miles until it gets really hot. Maybe I'll switch to 5w-30 (from 5w40) and see what I gain.
EMD-Run8 said:It costs less than Redline, Royal Purple, etc![]()
ViperQA1 said:It just gets too hot here for thin oil.
You missed the point. The 5w30 is thicker, yes THICKER at high temperature than 15w40, because the slope on which viscosity decreases vs. temperature is flatter. That's what Cummins was showing in the graph, that by using 5W30 (and even more so 5W40) it would actually be thicker at higher temp, therefore costing you a little mileage vs. 15w40, which gets thinner at 230deg than 5w30 and 5w40. I said that since about half my miles are at lower oil temperature, I prefer to gain mileage at cold temp. with my 5w40 and to lose a tiny bit at high temp (vs 15w40). I also like the extra protection when warm, of a thicker oil, rather than the water thin 15w40 at 230 deg.
Coolslice said:If you really want a mileage increase, use Amsoil and buy the Tornado to go with it. . :-laf
betterthanstock said:You missed the point. The 5w30 is thicker, yes THICKER at high temperature than 15w40, because the slope on which viscosity decreases vs. temperature is flatter. That's what Cummins was showing in the graph, that by using 5W30 (and even more so 5W40) it would actually be thicker at higher temp, therefore costing you a little mileage vs. 15w40, which gets thinner at 230deg than 5w30 and 5w40. I said that since about half my miles are at lower oil temperature, I prefer to gain mileage at cold temp. with my 5w40 and to lose a tiny bit at high temp (vs 15w40). I also like the extra protection when warm, of a thicker oil, rather than the water thin 15w40 at 230 deg.
click here, then go to page 12:
http://www.everytime.cummins.com/every/pdf/MPG_Secrets_Whitepaper.pdf