Winter rating in multigrade - with a tropical twist

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Hi folks,

First time poster here. I searched all over the internet but it seems I'm the first one to ask this very specific question:

It's clear that all other things being equal, a lower "W" rating is preferable (e.g. 0w-40 better than 15w-40). However, almost all information refers to places where temps drop significantly in winter. So, what about tropical countries which have basically constant temps all year? Where I live a "cold" start is at worse done at 15 Celsius (59 F) but the average start is probably closer to 25 C (75+ F), where the advantages of a lower "W" rating are perhaps not that significant. This is made more complicated for the fact that wider range multigrades are sometimes harder to find or considerably more expensive.

I found this table (not sure how accurate) which shows how viscosity behaves at specific temps and after 20-25 C is basically a wash, mostly so if you look at the 10w-30 and 5w-30 lines (same hot viscosity):

graph_4_viscosity_comparison.jpg

Reference: https://www.kewengineering.co.uk/Auto_oils/oil_viscosity_explained.htm

Some folks around here argue that using too high of a W rating here is risking engine damage. My counterargument is that the money/effort spent in searching for that lower W rating is not worth it vs simply buying a good quality oil which has better properties protecting from cold starts via baked-in additives or simply better engineering.

Is my reasoning wrong? Down here the standard (for better or worse) is 20W-50 and I bet most cars 5+ years old get it as default (think of it as the 30psi tire pressure). You don't see those engines blowing to pieces or needing a rebuild constantly so I'm really curious as to whether or not that extreme 20W oil is actually not too bad for the local conditions (of course leaving the 50 grade out).
 
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Some folks around here argue that using too high of a W rating here is risking engine damage. My counterargument is that the money/effort spent in searching for that lower W rating is not worth it vs simply buying a good quality oil which has better properties protecting from cold starts via baked-in additives or simply better engineering.
Only if you are below the pumpability limit for the grade. It's all about temperature, that answers most of everything you posted.
 

Eric_GM

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Thanks. I do understand that at a high level but I'm not that familiar with pumpability values and don't know if, say, in the table above the 582 Cst viscosity at 20 C is on the low or high limit for the average engine. I would say that temps around here drop below 20 C (and stay in the high teens) perhaps once or twice a year.
 
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Perhaps I have a rudimentary understanding of this. Being I'm in central FL which is close to OP's weather parameters, 5w would be negligible compared to a 0w during the Summer, and maybe even during the 4 days it gets below 40 degrees here in February. So 5w20 would be behave nearly identical to 0w20. It is about the ambient temperature, but we always want to consult our owner's manual.
 
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Winter rating is only relvant if below freezing, I run 5w20 simply out of convenience in CA. Main reason OEMs are specing 0w ratings is its usually synthetic. But even in the Equinox they spec 0w20, I run dexos 5w20 - runs the same.
 
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Thanks. I do understand that at a high level but I'm not that familiar with pumpability values and don't know if, say, in the table above the 582 Cst viscosity at 20 C is on the low or high limit for the average engine. I would say that temps around here drop below 20 C (and stay in the high teens) perhaps once or twice a year.

SAE J300 tables give a good clue...


Notice the pumpability limits... 60,000 cP. cP is a dynamic viscosity unit, and is the same as cSt x density. oil density is below 1kg/dm3 so cSt will be above 60,000 at the pumpability limits...

In other words, you can't buy a properly formulated engine oil that's too thick at 15C. Not even straight grades.
 

SR5

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OP, a 10Wx oil (like 10W30) is good down to 0F (-20C), with 5Wx and 0Wx suitable for even colder starting temperatures. The sort of temperatures that you or I will never see, I also live in a warm (hot) climate. I can use 15W40 or 20W50 year round, and I often did. When I went Outback years ago, I ran a 20W60 mineral oil, just to be sure. Now days I would be content with a 5W30 synthetic.

If you consider a 5W20 and a 0W20 that are formulated the same, then the narrow grade (5W20) should be more shear stable and have a lower Noack volatility. Both good features.

In reality the 0W20 is probably formulated with better base stock, like PAO or GTL, meaning they would have similar Noack and shear stability. Similar comparing a 5W40 synthetic to a 15W40 mineral, they would use very different base stock, but both would be good oils if correctly formulated.

They are both xW40 grades, and should behave the same when warm. Obviously the 5W40 oil is better for starting at extreme cold temperatures, but much colder than you or I will ever see, so not a concern for us.

A well formulated 15W40 car oil (PCMO) is a very good oil, read the thread linked below, they are just not very common in North America, so not often discussed here.

 

ZeeOSix

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So, what about tropical countries which have basically constant temps all year? Where I live a "cold" start is at worse done at 15 Celsius (59 F) but the average start is probably closer to 25 C (75+ F), where the advantages of a lower "W" rating are perhaps not that significant. This is made more complicated for the fact that wider range multigrades are sometimes harder to find or considerably more expensive.
If 15C is as cold as it gets, then 10W and 15W oils would be plently thin enough for cold starts.

Some folks around here argue that using too high of a W rating here is risking engine damage.
At 15C cold starts? 😂
 

Eric_GM

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Thank you all, extremely useful info all around!

So basically what I suspected is right, W rating is negligible around here, but I should stick to the required oil grade for the engine (as I've been doing since forever). Seeing folks from Down Under and Florida replying here makes it more surprising that this is something people don't ask often (or ever). PD: The mystery country is Costa Rica, btw.

I once saw this Mobil 1 which I believe is the widest range multigrade I've ever seen locally (I guess even crazier ranges exist). Shame they didn't have enough for what I needed:

8114a0a2-bf43-4f23-b3a3-107f0f5a56ba_1.b3220ca0b1fa50357ebeae9b1ddaf44f.jpeg


Good stuff, guys. Thanks again!
 

SR5

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So basically what I suspected is right, W rating is negligible around here
Correct, the warmer the climate the less important the winter W rating. It's all about starting a cold engine below freezing.

To be honest, I don't like that M1 5W50 you showed, too wide a viscosity grade which means it's prone to shear (becomes thin due to mechanical stress). For you and I, the M1 15W50 would be suitable and far more shear stable in use.

The thing is, global car manufacturers often recommend wide grade oils, e.g. Mercedes Benz with their 0W40, because it works everywhere on the planet. It has 0W for starting in Alaska, and it's a 40 grade for a fast lap of the Nürburgring. It may not be perfect for every application, but it's never wrong.
 
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