Why do some cars call for 5W20, not 0W20?

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Feb 28, 2021
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There are numerous discussions on 5W20 vs. 0W20 motor oil. It seems to me that the common consensus is that 0W20 is better than 5W20 for engine lubrication, at least not worse, for oils of the same brand.

What has puzzled me is why some cars (slightly older models) call for 5W20 in their user's manuals, not 0W20? I suspect (in another thread) it was due to availability and price sometime ago, but never get it explained or confirmed. Hope someone can give a more concrete answer.

I sent an email to Honda for their Gen 2 Odyssey, but got a useless answer something like "Our engineering team determined that 5W20 is the oil you should use".
 
0w20 was just was not as popular yet. Slow baby stepping their way down the viscosity chart as mpg becomes more important and oil technology progresses. It's hard to break old mindsets as there are still folks who will not use anything 0w or w20 let alone both together. People who use the points spread basis to judge modern oils prefer the lower spread and still believe 10w40 is the fast shearing engine sludging oil of yesteryear and 0w20 is water that could never properly lubricate an engine.
 
My 2018 Mk4 Ford Focus 1.0 EcoBoost also calls for the 5W-20 with spec of Ford WSS-M2C948-B

I don't know why because a 0w-20 is a better oil in terms, but it must be a reason i would think.
 
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Slow baby stepping their way down the viscosity chart as mpg becomes more important and oil technology progresses.
0W-20 will theoretically use a couple drops less fuel during warm-ups compared to 5W-20, so ultimately it's probably really driven by the car companies trying to get 0.0001% better fuel mileage for CAFE credit.
 
In addition, maybe more importantly, 0W(-20) provides better lubrication therefore engine longevity during start up, especially in a cold environment.
 
I have one car that allows 5W20, 5W30 and 10W30 and no mention of 0W20 and have another car that says 0W20 only and says use 5W20 if 0W20 is not available but change back to 0W20 quickly or next time.

Assuming that 5W meets the cold temp spec. so there is no technical reason to select 0W over 5W:

One reason could be the OCI. I think the longer the recommended oci, the more chances of 0W-20 being specified since you can formulate a more inferior 5W20 (e.g. blend) but it's hard(er) to make an inferior or "cheap oil" with 0W20 which has a superior base oil. So the longer the oci, the more of "synthetic" oil requirements (i.e 0W).

price diff between 0 and 5W could have been another reason in older days but it may no longer be an issue. So if the recommended oci is shorter, there is no need for pricier 0W.

Some say 5W20 has less vii and it's better ... I rather take 0W20 with naturally higher vi than risk it with some potentially inferior 5W blend.

I've also read that some designers (old-timers?) prefer less of a pao, ester or higher group oils and prefer more of lower group (III) oils or "syn-blend" as they are more seal friendly, etc. ... This is just a wild guess and something I've read here and there on the internet. Not sure if I believe it 100% :)

Basically I think oci maybe the main factor. I am a thickie and like oils with less spread but in this case, if I had to use a 20, I would never use 5W20. However, I don't mind using 0W20 even though it has a larger spread.
 
I am a thickie and like oils with less spread but in this case, if I had to use a 20, I would never use 5W20. However, I don't mind using 0W20 even though it has a larger spread.
Could you please elaborate "0W20 has a larger spread"?
 
Could you please elaborate "0W20 has a larger spread"?

xW-y spread is y minus x.
For example 5W-20 spread is 15 as opposed to 20 for 0W-20.

Typically the higher the spread, the more viscosity modifier (viscosity index improver) is added to the oil.
 
0W-20 will theoretically use a couple drops less fuel during warm-ups compared to 5W-20, so ultimately it's probably really driven by the car companies trying to get 0.0001% better fuel mileage for CAFE credit.
You mean try to save a half pint of fuel over 20K miles of driving? lol
 
You mean try to save a half pint of fuel over 20K miles of driving? lol
And that would only apply for a very few seconds during starts at extremely cold temperatures that applies to a small segment of the world during short periods of time (-35F and below). One struggles to think the half a pint over 20k would apply to even a significant portion of the population.
 
Care to elaborate?
Most wear occurs during warmup before the oil's additives are fully functional. Wear is a result of insufficient film thickness and that's not an issue at startup. All oils provide sufficient MOFT at cold temperatures.

And what do you mean by better lubrication? A Group II base stock is a better lubricant than PAO for example.
 
Wear is a result of insufficient film thickness and that's not an issue at startup.
So you mean a sufficient amount of oil file already exists at all important interfaces as soon as engine parts start moving? It does not take time for the oil pump to supply the oil?
 
And that would only apply for a very few seconds during starts at extremely cold temperatures that applies to a small segment of the world during short periods of time (-35F and below). One struggles to think the half a pint over 20k would apply to even a significant portion of the population.
I was being a bit sarcastic, perhaps exaggerating a bit. It might equal a pint of fuel saved ;)
 
So you mean a sufficient amount of oil file already exists at all important interfaces as soon as engine parts start moving? It does not take time for the oil pump to supply the oil?
As long as the winter rating is not inappropriate for the starting conditions the oil will be pumped.
 
Will it take longer for the 5W20 to get to the interfaces than for 0W20?
No. Only if you are below the gelling temperature of the oil and it causes the pump to cavitate. That would be somewhere below -35F.

It's a common misconception on the Internet that "most wear occurs at startup", typically because it sounds like it should be so. There are some pretty long threads on here discussing that, look for the ones where user Shannow was a contributor.
 
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