You can't go wrong with any top brand 15W-40. My first choice would be Schaeffer's syn blend. Among the readily available oils, I'd pick the Conoco/Phillips/76/Kendall oil with their exclusive Liquid Titanium additive. It seems to be something real, not just marketing hype. (I'm sure all the other oil makers will have something similar and equal soon.)
You need to see if GM is now approving any 5W-40 oils for this engine. The minimum HTHS viscosity for 5W-40 is lower than for 15W-40, so that might be the reason GM didn't approve this viscosity. If GM does approve 5W-40 HDEO, pick any top brand and you can't go wrong.
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I don't know for sure, but I would assume that GM has approved the 5W-40 viscosity in these engines as many people are using RTS 5W-40 or Mobil 1 TDT. The local Chevy dealer here uses only the RTS (Rotella syn) for synthetic oil changes. They use Delvac 15W-40 for conventional oil changes.
The Schaeffers offerings are CJ-4 and are excellent, both the 15W-40 blend and the 5W-40 full syn. Plus, when purchased in $350 quantity, shipping is free, making it lower-priced than all the other synthetic oils, even RTS. If you decide to go for the Schaeffers, get with the site sponsor here, Mark, screen name 'salesrep' for very good service. I just received 3 (6 gallon) cases of 15W-40 blend and a case of fuel additive not long ago. It's hard to beat Schaeffers for quality AND price. Plus the convenience for me of making a 5 minute phone call to get the stuff delivered a few days later.
I'm going to be using the factory OLM setup.
I will more than likely use synth, just wondered if anyone knew of any issues I should be aware of.
I have learned from both here and others that this engine is not hard on oil at all.
Peruse the UOAs here and over at dieselplace.com, and you'll see that for 10k miles OCIs or less, the Dmax can produce stellar results on quality dino oil and filters. No need for synthetics, when you're in FL; it's not like extreme cold starts are a problem, nor is extreme heat.
(note: moving thread to HDEO where it belongs - MOD)
I would not put a synthetic HDMO in a new Duramax until about 10,000 miles. With diesels you have to allow time for valves to set and rings to break in. Synthetics will slow down the process. Other diesel engine companies suggest not to run synthetics till after 20,000 miles. Also don't let your new Duramax idle more than 5 minutes during the break in period. I would run full synthetic in the Allison from day one and most dealers are ordering that way now but double check.
I'll be the first to call bunk on the synthetic mythologies ...
Plenty of companies using it (in gassers) right from the factory. Are diesels different than gassers? In cycle operation, yes. But in machining technology and materials used, not really.
What's up with the 5 minute idle comment? Are you referring to the DPF cycle? Sure it burns more fuel during regen, but there are times when people leave the vehicle running for convenience; to keep the vehicle cool or warm. Long idle periods used to contribute to "wet-stacking" in older IDI diesels, but today's common rail, electronically controlled, injection systems don't have near as large an issue. It's there, but nowhere as bad as it used to be. And synthetics have nothing to do with this one way or another.
Further, I don't know of any "dealer" that order the trucks with "synthetic" for the Allison 1000 series in the 2500/3500 GM vehicles. There is no transmission fluid RPO; these come straight from the Baltimore facility with DEX VI in them now, which is stardard GM factory fill in all their applications for cars and light trucks. The Allison 1000 built in Indy is supplied for the TopKick/Kodiak trucks, and used TES-295 from the factory. But again, there is no RPO. You get what you get; there is no "optional" tranny fluid.
And where's the logic in suggesting not to use synthetic in the engine right away, but proporting it for immediate use in the tranny? Do you think trannies don't go through a break in cycle?
The rear differentials come with synthetic GL-5 in them from GM (commonly called "grape juice"). Would you suggest removing it for "break in", and then changing back to synthetic again???????????????
Synthetics extend drain intervals. Synthetics survive extreme temps better (and I mean E-X-T-R-E-M-E). Synthetics don't grossly affect break-in.
That's my take on it.
Lets don't get off track. If you read other diesel engine company's manuals they suggest not using synthetics for a length of time. I'm a huge fan of synthetics and everything I own down to my lawnmower has synthetics in it. Allison trans come from the factory with Dexron VI ( Petro- Canada ) in it up to the 4500 trucks and then they put in the TES295 Castrol. Diesel engines are a lot different than gas and should be treated as such. The Trans and rear end I use synthetics in it from day one and I would recommend synthetics in any diesel engine after the recommended break in time. Until then use a high grade oil like Rotella T.
Many diesels come with synthetic from the factory, and that's all you can use. Every modern Euro passenger diesel I know of is this way.
The fundamentals are the same for a turbo diesel as a turbo sparker as far as break-in. Boost it and heat it up. Plenty of those use synthetic from the factory. Not using synthetic during break-in is a myth. It might have applied years ago, but it sure doesn't now. Machining is many times better now.