Using Synthetic 5-40 Oil

I just saw Wal-Mart selling Rotella-T 5-40 full synthetic oil for $10 a gallon....but is it safe in a Dmax this time of year?

I read that GM is adamant that 15-40 is critical except in very cold weather.

There are a lot of DP members using Mobil 1 Delvac or Shell Rotella Synthetic, both are 5w-40.

I am using Rotella Synthetic. I do not tow, but I zip along quickly in warm weather on interstates. At idle, I see a bit under 30 psi oil pressure, and at 2000 rpm see 60 psi, which is essentially the same as what I saw with 15-40 conventional oil.

It was funny when I bought this truck. I thought I knew more about it than the salesman. He also expressed reservations about 5w-40 oil, but then told me about all of the aftermarket performance enhancing boxes that I could add, just make sure I remove them before bringing truck in for warranty work. ;)

Obviously, since I use it myself, I think that the synthetic works fine year round and does no harm, at least if you don't tow heavy loads. I wonder if anyone on DP has done an oil analysis of their Duramax oil with either Delvac 1 or Shell Rotella Synthetic?

[quote]The correct oil filter for use on the Duramax 6600 engine is the AC PF2232 or the production oil filter, GM P/N 97214983. This filter was designed specifically for use on the Duramax 6600 engine and incorporates improved filtering capabilities as well as an integral oil pressure relief valve. The oil filter should be torqued to 24 N.m (18 lb ft) to prevent leaks under high pressure conditions.

Oil Viscosity for Cold Weather Operation

SAE 5W-40 viscosity oil designated as API CH-4 or CG-4 should be used if the ambient temperature falls below -18

The 5W is the rating of Delvac 1 relates to cold weather operations and not its normal operational viscosity. Since Delvac 1 easily flows to 40 below zero, it meets the 5W(winter) specification. One of the many benefits of full synthetic oil is its viscosity stability. It does not 'thicken' with cold temperatures or 'thin' with high temperatures as does conventional mineral based oil. (it does but to a *much* lesser degree) Thus we gain all the advantages of having excellent lubrcation on cold start-up yet unequalled protection at high temperatures.
Delvac 1 is not a 'thin' oil; the base stock used to make Delvac 1 is actually 'thicker' than the base oil used to make a conventional mineral based 15W-40 engine oil.

As example: military 'special' vehicles that may be assigned for immediate service anywhere/any climate in the world, are initial filled with Delvac 1 as the vehicle is equipped for deployment for any environment, arctic or desert.
George

AW Shucks George, This is why we love you man! :D

Delvac 1 and a good (Harvard) bypass system will yield excellent results as has been documented through ferrographic analysis AND particle count on my Dmax...

Thanks for the responses, they have been useful.

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