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Cold weather oil weight

I have a 1999 CHevy Silverado V8 which I will be changing the oil in soon. This is the first time I have changed the oil in the truck (note, not the first time the oil has been changed, just the first time I have done it :-)). Anyway, I am trying to figure out what weight oil to use for the winters up here, it regularly drops below zero, and can go as low as -50. However, I still have a few months of “reasonable” weather before we get to those extremes. Reasonable being between 20 and 60 degrees.

Check your owner’s manual for the specifics, based on the temperature range you expect for your winter. 5W30 might work, but the manual may recommend something else, given the -50 or so you might get.

A quick search shows two themes: most recommend using a synthetic, and many use a 0W40 or 0W30 for the winter’s cold months.

First step is to check the owner’s manual. Chances are it will say something like 5WXX. The five is the low temperature ability of the oil. Lower is the low temperature rating and 5 is as low as you want to go. The other two numbers mean almost nothing until it get up to about freezing.

Assuming the recommended number starts with 5, you should be fine.

I’d consider a 0W-30 Synthetic for this kind of weather. It will still protect as well as a 30W, but will flow better at very low temps. I’d also consider a block heater for the -50 days.

Yeah, block heater of some type would be a major plus. Fairbanks, I’m assuming? I’d go with a full synthetic, 0W-30 if that’s close to your manual’s requirements.

I lived in grand forks, -46 was the coldest while I was there, and never used any weight different than specs for the vehicle, but definitely used a block heater.

Fifty below zero with any kind of wind? Nobody’s goin’ nowhere!


96 below wind chill, we moved on.

I would go with a 0W40 synthetic if the truck is used for heavy work, a 0W30 full synthetic is OK if the truck is used as a car.

Mobil 1 and other full sythtics and 0W40 has a “pour point” of lower than -54C or -66F!!!, so you should be OK even without a block heater. And you don’t need to drain it in the spring; the “40” part of the spec. ensures it has good heat resistance.

Shell’s Rotella T SB premium oil has 0W40 and 0W30 with a similar low pour point, and should be OK as well.

Keep in mind that in 1999 few car engineers in Detroit had any experience with 0W synthetic oils; I started using them (Shell’s Synarctic) in 1979, but had to shop around for it.

P.S. The Alyeska Pipeline Company standardized on Mobil 1 for all their vehicles. They cut the number of oils types down from 16 to only 4, because of the wider viscosity range of synthetic.

Heck, if you could find some Polar-Artic 0w-10 you could use it as long as the ambient keeps the cooling system at thermostat setting. But, to avoid the onslaught of flame throwers, I’d use a 0w-20 and use a block warmer.

Before the crew lights up on that too, keep in mind that M1 was brought to market as a 5w-20 and worked just fine in many engines.

Now a thing about the Dubbya number. No matter what anyone thinks, a 0w-20 is lighter than a 0w-30 …is lighter than a 0w-40 AT ALL SENSIBLE FLOW SITUATIONS. They will all will be within stress limits on the CCS (cold crank simulator) …which means that they WILL PUMP and not just spin around in a gelatinous mass on the pump gears. A “0w” is within the SAME LIMITS as a “5w” @ -5F colder. That’s it -5F colder. The W has nothing to do with operational viscosity WHATSOEVER. The operational visc is the 20,30,40. The “w” is just how it “reacts” at those temps. It’s not a rational thing.

Take a mixer that you put on your drill driver to mix paint. You’ll start forming circles that get slower and slower as they get to the exterior of the can. That’s shearing in laminar flow. The heavier the fluid …the thicker the layers of the circles. This is referred to as a Newtonian fluid.

At those temps, normal/sensible flow is not possible and instead of forming those neat progressive circles, stuff just wraps around the spindle of your mixer and climbs and never forms that shearing action, that’s when the fluid is referred to as a non-Newtonian fluid. That’s the realm that the Dubbya rating is dwelling in. It has little to do with any point where the fluid is actually flowing.

In any event. Use the lowest viscosity (top number) that you feel comfortable with that also has the “0w” rating. You’re one of he few people that might actually experience the cold properties of the fluid. Once flowing, each fluid will tax the energy to pump it in respect to their viscosity. A 0w-40 is at least 150% more “thick” than a 0w-20 at just about any temp once flowing. @ -35F …it can be quite a bit.

If your driving event is 15minutes or less, I doubt you’re in any sensible viscosity range. If it looked like a 70 weight, I’d be surprised.

Oh yeah: Don’t forget to let it warm up before driving. Even a synthetic won’t be properly protecting the engine in those temps until it warms up and thins a little. Plus your trans fluid, power steering fluid, differential oil, etc. are all going to be that cold. So take it easy on the truck when it’s that cold out, at least until it’s up to operating temperature. You might consider a full-synthetic lube for the differential too.

I had a Pontiac V8 in this kind of weather. Although it started easily with 0W30, it needed to warm up before I could move the automatic transmission shift lever! As pointed out, the other mechanical stuff will be very stiff, and you can’t just take off. But you already know that living in Alaska.

With front wheel drive cars with CV boots, I park with the wheels straight forward. That way I get a little straight running to warm up the rubber and the grease inside before it needs to bend when turning the wheel.