Just discovered that my last oil change I used Delo SAE 40, instead of 15W40. To be honest I have not understood the implications of running these different viscosities and their real impact on the Duramax. Can anyone fill me in on what problems I might run into? Its been running on SAE 40 since the last oil change at 35000, now 40,000 just doing the oil change now. Thanks.

Assuming it has all of the same detergents as the multigrade, running a straight 40w oil as oppossed to a 15w40 multigrade with the viscosity improvers - really nothing. Most of the industrial machines we assess run either a 30 or 40w straight oil. In June in CA running a straight 40 weight oil should not have any detrimental effects whatsoever. http://www.dieselplace.com/forum/smileys/Geek.gif

The Delo 40 does not meet the required API specifications, however, beyond just the multi-vis aspect but additization, etc... Again, straight 40W in CA, as previously mentioned, should be no great problem but....
Best to use the optimum oil vis, not only for running, but for start-up, which the 15W portion of the specification provides..
I would suggest changing to the appropriate multi-vis as soon as practicable and consider it a good relatively inexpensive engine flush.
George Morrison

Thanks for the info. I've obsessed over the maintenance of this truck and changed the oil every 3K, now lengthening it to every 5K, done the chassis lubes every other oil change, changed the diff oil and transmission flush. So I didnt feel too good about pulling a bonehead move and not checking the viscosity of the oil. Anyway you guys made me feel abit better. The oil is being changed out today.

I was worried about you George - nice to see a post from you.

Ditto

Good to hear from you George!http://www.dieselplace.com/forum/smileys/Approve.gif I've also been wondering where you were.


Steve