Originally Posted By: Jetronic
Since the truck is used for towing, I'd go for a thicker 5w-30. Are there any available to you for a decent price that have an ACEA A3/B4 rating. The variable displacement oil pump has no issues with higher viscosity oil, it works during the warm-up of the engine, doesn't it? Viscosity also has no bearing on the Start/Stop functionality.
Your current oil ended up way out of spec, viscosity wise, it should not be lower than 9.3 cSt. How thick was the Mobil originally, I would expect 10 cSt at least? That means you lost over 20% in kinematic viscosity, which equates to 10% HTHS loss if the cause was permanent shearing. With fuel dilution the HTHS loss is likely higher, closer to 15%. If you get the same percentage drop with an A3/B4 oil (not likely) You'll still be in spec for a 30 weight oil. I guess the start/stop and oil pump don't mind thin oil either?
I don't understand where Blackstone gets it "should be values" from, probably from the universal averages.
How is the oil cooler setup on these engines? Is it an oil/water cooler or oil/air? In any event though, the oil will be significantly hotter than the coolant, close to 250 degrees on those sections where the transmission downshifts and rpms go up over normal (if you have those). I'm sure you know the oil temp in the hot spots will be even higher.
Lots of good thoughts here, I'll try to break my response down similarly.
From my understanding of the variable displacement pump is that it will work based on the engine's needs, not just during startup.
I haven't been able to map all the scenarios in which the auto S/S will not work but my concern with thicker oil is the delay in getting where it needs to go under successive startups. See how well hybrids perform with 20wt oil.
For the pump and auto S/S system not minding thinner oil. It is almost certain that lower viscosities were seen in testing and thus indirectly (possibly directly) validated.
The oil cooler is an oil/water cooler. The only time rpm ever goes over 3k is during engine braking when coming to a stop. The standard spot is around 2200-2300 rpm in 6th gear. I am very interested to see what the actual oil temps are. With a large 6qt sump it should help to keep the bulk heat down that is introduced even with the piston cooling nozzles. When I'm bored one day I'll probably throw in an oil temp monitor just to see what is happening. But with coolant only rising 6 deg_F with the turbos and partially integrated exhaust manifolding being cooled I have to imagine there isn't a lot of left over heat.
imgurl
