Current Temps In Louisville, KY:
Feels Like -4°F
UV Index: 0 Minimal
Dew Point: 1°F
Pressure: 30.15 inches and rising
Wind: From the West Northwest at 9 mph
Just started the truck up here awhile ago...and I'm running Pennzoil Long-Life 15w-40 in my 4.3L Chevy, and although it definitely does crank slower, I have no "funny" noises on startup and oil pressure comes up almost immediately.
Considering this, I'd say a HM10w-40 is at least good to these temperatures.
[ January 30, 2004, 10:17 PM: Message edited by: Jelly ]
I am running Valvoline Maxlife 10w40 this winter. I am right outside of Detroit, Michigan, so it dosen't get as cold by me as farther from the city. I cheat, though, with an oil pan heater (250 watt) for at home, but do get cold starts at work. Today it was around 15F and it had sat for 9 hours. No noises on start up, cranked fine, but the mechanical oil pressure gauge needle didn't leave the zero mark for about 3 seconds. Then it takes a few minutes for the cold oil pressure to reach what it normally reaches in less than half a minute. I think I have started as low as 10F on a 9 hour cold engine and it was about the same. Had some cranking problems, but adding a pint of water to the battery solved that (4 year old maintenance free battery).
Not sure what you mean on oil consumption. That is more a function of engine condition and/or thickness and quality of the oil.
Per spec sheets, conventional 10w-40 typically has a Borderline Pumping Temp of -22F, same as 10w-30, but this degrades quickly along with the Pour Point. The old-school owner's manual cut-off point for 10w-40 was typically 0 (zero) degrees F: Temps colder than this called for 5w-30.
There are limits to when a 15W-40, 10W-40, etc should be used. This has to do with the MRV (Mini Rotary Viscometer) and MRV BPT (Borderline Pumping Temp) test values.
The absolute MRV limit is set at 60,000 cP: approaching or beyond this "yield stress" the oil can no longer flow into the oil inlet.
I don't have data for the oil you're using, but I do have the Esso recommendations:
Their 15W-40 oils generally have a Yield Stress at around -30 C / -22 F, though Esso also recommends they not be used colder than -20 C / -4 F in most motors.
The Esso HDX Plus 10W-40 and Esso Protec Extra 10W-40 is MRV BPT at -28 C / -18 F.
Remember also that different motors have different reactions to higher MRV values. Some motors may be fine right up to the Yield Stress. Others may require an MRV value quite a bit lower to avoid low oil pressure and noises.
All other things being equal, generally a heavier-grade oil, say 10W-40 or 15W-40 or 20W-50, will reduce oil consumption compared to especially a regular 5W-30. Their base stocks have less volitility than a regular 5W-30, hence less oil consumption.
Since synthetics have less volitility, they also have lower oil consumption. If you're really worried, and want better cold temp operation, use Mobil 1 15W-50.