I'm about ready to make the switch to Amsoil. My question is should I go with the Heavy Duty Diesel/Marine 15W-40, or the Series 3000 Heavy Duty 5W-30? The extra money for the Series 3000 isn't really an issue, I'm just wondering if I will benefit from it. I live in the San Diego area, not exactly a cold climate, but overnight temps do drop down around freezing in the winter. Most of my driving is just the 20 mile (one-way) commute to work, probably 75% city. But I do tow a good amount during the winter months. <br><br>What do you guys think? Which would be better for my application?<br><br>Thanks

 

15/40<br><br>Don~

 

15w40

 

15w-40 all year.

 

Chevron Delo 15w-40w.... ;D ;D

 

15W-40.<br><br>I've used both, I'm happier with the 15W-40. If there's an mpg difference, it's hard to measure; the 5W-30 had more blowby; oil analysis results show no significant difference, and I don't have second thoughts about &quot;using the weight recommended in the owner's manual&quot; or &quot;running hard in hotter weather&quot;. If I were expecting continuous temps below freezing, like in teens, I'd reconsider. But it started fine, with 15W-40, in high teens this winter.<br>

 

15W-40.<br><br>Using a synthetic in cold temp IMHO negates the need for a lighter weight oil in the cold.<br><br>Since a 15w-40 synthetic will still flow at -40F, I would say that it is truly a year round oil no matter where you live (Arctic being a possible exception)<br><br>HOHN