So I have a question about how viscosities correlate to temperature ranges in real world use. I recently read that while a 0w40 meets pumpability requirements at the -35C to -40C range that outperform a 5w30, the 5w30 often has lower viscosity around 0C than the 0w40. I had thought that a 0W oil would outperform a 5w oil for cold flow at pretty much all temperatures below 40C. If that is not the case, is the common BITOG member recommendation of Mobil 1 0w40 in place of a 5w30 in many gasoline truck engines actually causing more engine wear on cold starts?
Oil Viscosity Basics: 0w40 vs 5w30 Cold Start
- Thread starter brandon9715
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No. 0W-40 or 5W-30 will work fine in northern North America winters for cold start protection. Just curious, what engine are you thinking of using it in? Now a 0W or 5W-30 may raise your MPG at operating temp a little compared to a 0 or 5W40 weight, but not enough to notice. If you are having issues with the cold starts, maybe install a block or oil pan heater and battery warmer. I have watched some videos and read about living at the coldest places on earth, and I am sure those people use a 0W oil in their cars. Some of those people literally wrap their vehicles up in thermal blankets overnight so they will start hours after shutting them off. Others just leave them running.
Vehicles in question are my 2015 F150 with the 5.0 and my dad’s 2016 F150 with the 2.7. I’m referring specifically to moving up on the hot viscosity designation and down on the cold viscosity designation. Is a 0w40 more viscous at 0C than a 5w30 at 0C (or vice versa)? I’m seeing conflicting information. Since oil viscosity isn’t linear with temperature, I’m seeing some information that a 0w40 could actually be more viscous during cold winters than a 5w30 if the temperatures aren’t down in the extreme negative temps.
I am not educated enough to give you a proper answer, though there are some here at Bitog that are. I do know either will be fine for cold start engine protection. Generally speaking though, the first number is related to the cold temp viscosity, 0W being a little thinner than a 5W in cold temps. There is more to this however, and I am not educated enough to get into the nitty gritty.
The thing is, “cold flow” doesn’t matter much as long as the oil is pumpable. Such is the nature of a positive displacement oil pump found in vehicle engines. If the oil is at or above the minimum temperature specified by its winter rating, sufficient volume of oil will flow through the engine regardless of viscosity. At some temperature below the minimum temperature specified by the oil’s winter rating, the oil becomes unpumpable (starts to gel) and engine damage will occur.
Above that minimum temperature, it is not certain that a specific grade will “flow” faster or slower than any other based on SAE grade and winter rating alone. You could possibly look at viscosity index for some indication of that, if you can find that value published, with a higher index indicating that the oil viscosity changes less with temperature. Thickened, but pumpable, cold oil protects adequately.
The exception to cold flow not mattering is possibly if you do a cold start close to the minimum temperature rating and immediately go gas pedal to the floor. In that case you can send the oil pump and filter into bypass and partially restrict oil volume flowing the engine, and risk sending what is flowing through unfiltered. It will probably warm up quick and not be catastrophic though. Best practice is to drive reasonably until achieving normal operating temp.
4wd
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Early in my time here - I posted something about flow distribution being different at that point - I will post both the initial response - and what I have posted since then to help think about how oil flows …
4wd
$50 site donor 2026
I’d make sure LSPI is a consideration for the power intensive turbo … it becomes a bit more grey in the 40’s and 0W’s - whereas most of 5W-30’s will be SP/SQ and dexos …
It would be fun to take a quart of each one and leave the oil outside where it's very cold then pour them both at the same time and determine if there is any difference.
The test you see on YouTube where they freeze oils to an exact same temperature and watch how long it take those steel balls to reach the bottom. I am guessing the 0W-40 would reach the bottom first before the5W-30. @dlundblad could be right though.
dnewton3
Staff member
I don't know about "fun", but it would not really be a valuable thing in regard to understanding anything with respect to wear. But it may tell us how quickly you could fill the crankcase after an OCI if you left the oils out in your trunk. Other than that, it's just PF junk science.
4wd
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Yes, I still have an old jug from calcium crazy days - might mix it 50:50 with new stuff and use where safe - only own one of four that’s turbo and it’s dual point injection …
Things are easier to start with 0W40.
4wd
$50 site donor 2026
This is the point where that big buck stops eating and starts looking around - but your crosshairs are locked
It depends upon how an oil gets it's winter rating. If it's lower due to the base oil's characteristics, did they have to use viscosity index improvers to get the operating temp weight? If so, what kind of viscosity index improvers? Did they have to use pour point depressants to get the winter rating that it achieved? If so, they may not need as much, or perhaps not any, viscosity index improvers. Then, there is the difference between base oil types. Some base oils simply have a wider spread between the winter rating and the operating viscosity range, and use neither pour point depressants nor viscosity index improvers. I GUESS that's what High Performance Lubricant's straight 40 weight oil is: uses nothing. However, I've seen it written that it is pumpable down to the 15w range. Not all straight 40 weights are pumpable down to those temps.
SO, it depends on how they achieve the winter and operating temp numbers as to whether one will be more viscous at freezing then another...you'd have to look at them case-by-case to know for certain.
SO, it depends on how they achieve the winter and operating temp numbers as to whether one will be more viscous at freezing then another...you'd have to look at them case-by-case to know for certain.
Check out the Widman calculator suggested earlier and plug in your oils' values.
FWIW I ran Amsoil 0w40 in a 2013 F150 5.0. It ran very smoothly and I did not notice any change in power or mpg.
I have wondered about this same question. When you are trying to start an engine in single digits F how does 0W30 compare to 5W20, 0w40 vs 5W30. Sure the oil is going to pump but will it be a significant difference in how hard it is to turn the engine over. Will it make the difference on an iffy battery.
My wife fell in love with a Yukon with the 'la Grenade engine that requires 0W40 now. For the sake of science I put half bottles of 0W40 and 5W30 in the freezer overnight and checked them the next day. The reading with my Mark1 Eyeball viscometer says they are too similar to tell which is thicker.
My wife fell in love with a Yukon with the 'la Grenade engine that requires 0W40 now. For the sake of science I put half bottles of 0W40 and 5W30 in the freezer overnight and checked them the next day. The reading with my Mark1 Eyeball viscometer says they are too similar to tell which is thicker.
4wd
$50 site donor 2026
The newer 6.2’s don’t … they ran the VIN on my buddies late ‘24 ZR2 and changed the oil with 0W-20 … tows and beats on it off-road
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