I did some checking on the way into work this morning.
Local temps were high teens this morning, for reference.
Most of you know, but for the record I run 10w30 dino HDEO.
* Upon startup, oil pressure heads to about 94-97"ish" psi at cold idle (hard to tell since the gage is not well marked). I sit and idle for no more than 15-30 seconds while I get situated, belted, etc.
* While still cold and driving at about 10 mph down my 1/2 mile long driveway, the PSI stays around that 90+psi range.
* As I accelerate down the county road, it's already viscosity shifting and the pressure will go to around 70 psi, even at 2000 rpm when the Allison shifts gears.
* Within two miles of driving, the oil pressure is already rising and falling with the rpm changes as I slow down for turns and then accelerate again.
* Within a few more miles, the engine is perhaps 180 degF and the oil pressure is almost settled. The engine will continue to work its way up to about 200 degF.
Once warmed up, this is where my pressure runs:
* When driving at 60mph, I sustain a steady 40"ish" psi at 1450 rpm.
* When driving at 65mph, I sustain a steady 45"ish" psi at 1600 rpm.
* When sitting at a stoplight at idle, it will be about 30psi at 700 rpm. Even last year in the stupid heat of AZ and UT when pulling my travel trailer, it never dropped below 28psi at a stoplight.
* When accelerating firmly, the pressure will jump up to around 60 psi, if I get the rpm's above 2,000; it is very consistent in that manner and will essentially hold that 60psi "ish" pressure, no matter how much above 2,000 rpm I push it, once it is warmed up.
I will note that the old hot-rodder addage of "10psi per 1000 rpm" typically does not apply to a normal engine, and certainly does not apply to a diesel today from my experiences.
Many of us converse with local Dmax owners, as well as compare notes here at BITOG. It is my general perception that 60 psi, when warm at a steady moderate cruise speed, would be "high" contrased to normal results. The Dmax oil pressure will see a very significant response as the rpm moves from 1400rpm to above 2000rpm, but it seems to be fairly predictable overall.
I run the 10w30 dino for four reasons:
1) just to be different and shock the "must use 15w40" crowd
2) compare/contrast wear protection to thicker fluids and syns
3) gain any mpg I can find
4) easier (quicker) starts in uber cold temps (self-defined as below -15F, which are admittedly very rare in IN and only happen once a decade or so)
In my quest, I have found that there is clearly no discernable difference in wear protection; the Dmax simply does not care what's inside as long as it's a qualified HDEO. Further, when cold, the oil pressure seems to be a bit lower with a thinner HDEO, and therefore I presume it flows sooner and "better". But that is a moot point because the wear data I have shows no advantage overall in that manner. So my only "benefits" seen with thinner grades would be to continue to annoy the "thicker is better" crowd, and to gain (perhaps imperceptably) some mpg. I might also be getting a bit quicker spin up, which is easier on the batteries and starter, but it's been so long since I've had a 40 grade in the crankcase I've somewhat lost my perception between the two choices; any gain in that manner would be almost moot in my normal low temps.
I guess what I'm saying, Charles, is that your gain of a bit of pressure really won't make a hoot of difference in more or less wear. This really is anecdotal; it's an interesting side bar but really won't manifest into anything noteworthy as far as wear in the engine.
What I find interesting is the fuel economy. Your mpg gain is enviable, but I cannot explain how you achieved it, unless the TDT you put in somehow is not the full 40 grade it purports to be (a UOA would answer this). To go from at 40 grade syn Amsoil to a 40 grade syn TDT really makes it hard to understand an estimated 7-8% gain. That is great for you, though; fuel savings is always welcome!
