Well I've my by 07 classic dmax for about a year now and I've been using Rotella 15w40 every 3k like "the book" says. Alot of guys here say that 5w40 synthetic is good year round but "the book" (my owner's manual) says not to use it in temperatures above 100 F. Well I live in AZ and I drive 6 months out of the year in 100+ temperatures.

My question is this ... Is anyone else using 5w40 in the Arizona summer in your d-max ? If so, are you noticing any problems with how it runs or how it starts up ?

Thanks

I live in surprise AZ and run mobil-1 syn 5w-40 turbo diesel truck oil. Mobil recomends it for 15w-40 applications. I looked at amsoil 15w-40 syn. but they did not pay to have it API certified, Mobil one did. I started running it at the end of last summer . Accoding to the dash guages it runs the same pressure and a the same engine temp. I Hope this helps.

One more thing, the dip stick only droped down one notch in 8000 miles. Basicly it used one quarter of one quart in 8000 miles.

Well I've my by 07 classic dmax for about a year now and I've been using Rotella 15w40 every 3k like "the book" says. Alot of guys here say that 5w40 synthetic is good year round but "the book" (my owner's manual) says not to use it in temperatures above 100 F. Well I live in AZ and I drive 6 months out of the year in 100+ temperatures.

My question is this ... Is anyone else using 5w40 in the Arizona summer in your d-max ? If so, are you noticing any problems with how it runs or how it starts up ?

Thanks

This is an age old question that has been discussed several times before. 15W40 is what the owners manual says to use. 5W40 is the viscosity usually for the synthetic oils. The only number that you should be concerned with is the 40W for your Arizona temps. When the engine is at normal operating temps, the oil is at the 40W viscosity (thicker) level. 5W40 is safe to use, and you may even notice a little better fuel mileage while using it. The 5W40 is usually used in colder temps due to the lower viscisity number of 5W (thinner). The 5 equates to a thinner oil when colder. Thinner is usually better for startups. This is all spoken in laymens terms. In any event, 5W40 is safe to use. It will not hurt our Duramax's.

On a side note, changing your oil at 3K intervals is overkill and a waste of your hard earned money. You may want to invest in an oil analysis at your 3K interval, and see if it is OK to extend your change interval to maybe 5K or maybe even 7500 miles. That has been the norm for being "safe" for a non oil bypass setup.

Lastly, I am moving this thread to maintenance and fluids as it is non engine specific. You will get better responses here! ;)

Thanks for the responses.

where does one get oil analysis done. do i just put some oil in a bottle and send it to someone? any help would be good. thanks

On a side note, changing your oil at 3K intervals is overkill and a waste of your hard earned money. ;)


Agree.

I change my oil more often, but if you use the DIC it works out to about 10,000 between changes.

where does one get oil analysis done. do i just put some oil in a bottle and send it to someone? any help would be good. thanks

I believe Heath, a vendor on the site, does oil analysis, and a few others as well. Also check blackstonelabs, stavelyfa, and avlubricants.

http://store.avlube.com/index.html

http://www.thesuperiorsynthetic.com/

Hope this helps. The two links are vendors here!