Oil and then Water questions.

[MaxACL]

I

[More Power]

In general, oil pressure will inversely follow engine temperature, meaning the hotter the engine - the lower the oil pressure. It has to do with changing viscosity - thicker when cold, thinner when hot. This affects diesel fuel as well, but that's another story....

I haven't heard of an oil pump failure on these engines. I wouldn't suspect it unless all oil pressure was lost.

Don't tow heavy with the grille cover on, no matter the outside temp. I wouldn't suspect a thermostat problem till you've towed in similar conditions without the grille cover. According to the literature on the Duramax, part of the reason for using two thermostats is for redundancy.

Jim

[Mark Rinker]

No wisdom or smarts here...just opinions...you know what they say...everyone has one (or two...)

All three Duramaxs I've towed with have widely varying oil pressures based on temp, load and RPM. In the heat of summer when towing heavy, the oil pressure at idle after a hard pull can drop low enough (on the gauge) to make you wonder whats up, but I've never seen a message, code, etc. on low oil pressure. I even had it checked out by the dealer on my LLY. The 2005 gauges will idle close to the red when its hot out, but you are nowhere close to the minimum spec of 14psi.

Today was pretty cold (5-10 degrees) and I threw the winter front on for a 500 mile roundtrip, half of it loaded with ~15K in tow. My water and tranny temps stayed in the 190-200 range, but the mileage SUCKED - about 7.5mpg loaded, and 14-15mpg on the way home with empty gooseneck trailer in tow. Extreme cold robs power - even with the winter front on. I agree with MP, though - you're on your own when towing with the winter front on. GM says its a no-no.

I run Mobil synthetic with 10K change intervals. Personally, I never touch the shift lever. I accept the gear and RPM that the ECM/TCM give me under all towing conditions. First trucks that I have never been tempted to 'control' shiftpoints with manual shifting. Your 5'r must be HEAVY, or a big wind drag to lug your Dmax down to 55...but not many mountains to contend with here in Minnesota.

[MaxACL]

Mark,
I have a ZF-6 and have to shift when I think the engine tells me to. I know diesels like RPMs.

Wish I could find Mobil 1 for my beast:)

Mike

[Mark Rinker]

Duh...sometimes my brain is thinking of a response faster than my eyes are reading.

The stock ECM/TCM programming on the Allison automatics does a good job of keeping the RPMs in the peak range of 1700-2000. I have found when I try to 'drive' the truck too much with my foot, that is when mileage really drops off.

I can still maintain good average speeds and mileage when towing with a bit more patience - when it comes to acceleration from 0 to 65.