Why Do Knowledgeable Folks on Here use 20 wt Oil

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As others have stated , it depends on factors such as the engine design , whether it’s a GDI fuel diluter or not and if a engine has a known problem with bearings or not (Hyundai Theta II 2.4L GDI) ? Besides the factory fill plus one run of QSUD 5W20 , my above Hyundai engine ran free and fast (although noisey) on 5W20 . A questionable low mileage OCI on 5W20 with fuel dilution , plus member suggestions and comments Hyundai moved up to 5W30 on the service of Theta II 2.4L engines caused me to jump up to 5W30 early on . Ideally , an engine oil should be thick enough to keep load bearing wear surfaces separated by an adequate oil film while sheer , possible fuel dilution and other factors may be in play to impact oil film thickness reduction . Lastly , as other smart members have stated - changing your oil regularly and erroring on the side of a lower OCI may be more important than whether you use a 20 or 30 weight oil (plus a good engine design where either a 20 or 30 weight oil is acceptable) . Gas mileage should not really be a factor in the 20 or 30 weight oil decision .
 
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The Y axis represents friction. The X axis represents N x v/L which is the "Bearing characteristic number" The transition is > .0000017.
v= viscosity N= rpm L= Load
Numbers under .0000017 are unstable and lead to mixed and thin film lubrication. With lower viscosity there is less cushion when loads increase like when shifting or hard acceleration. To me its just common sense.
That graph you call the "3 factor bearing graph" is actually called the "Stribeck Curve", and pertains to the lubrication regimes that exists between any two moving parts, not just journal bearings (Google it). Journal bearings behave per and are designed by the Sommerfeld equation, that's where the "bearing charactor number" comes from … it's the Sommerfeld number (Google that too). 😁

This thick vs thin thread has some steam, but I'll say what I end up saying in most of these threads. If the cap says xW-20 or lower, go up a KV100 grade because MOFT headroom is a good thing. Helps keep those top rod bearings and cam chains healthy. Most likely why Ford finally woke up and went from 5W-20 to 5W-30 in the Coyote sold in the USA. It was always speced for 5W-30 in some other counties. Ford trashed CAFE for more engine protection, like it should be. 😀
 
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Getting ready to head to VIR this weekend for a 2-day HPDE. A buddy tracks his GR Supra and I just found out he runs the factory recommended 0W20 and will be there...he has several track days on it so far....my prediction? Will be fine...
What's the definition of "fine"? Not taken back home on a trailer, lol. Guy on YT who tracked his car on the oil cap 5W-20 inspected his rod bearings after a few heavy track sessions and wondered why his journal bearings had so much wear. He thought it was a good idea to run the 5W-20 because he wanted cooler oil temps. 😄 🙃

The GR Supra probably has a good oil cooler, but going up a grade would still add protection.
 
There's a ton of multi run analysis threads and even ones comparing 30 and 20 in the same engine.

Here's two I found in 1 minute:
Even so thats not the way comparative quality analysis is accomplished between oils. The proper ASTM test doesn’t use a simple and uncontrolled spectrographic analysis.

People on here do but that doesn’t make it accurate.
 
Those are great engines, my daughter’s 2016 RDX has one. I use 0w30 and it’s never burned a drop of oil, knock on wood.
Lubrication is just one of the 5 functions of motor oil, - the main one - that gets all the attention.
Oil has to lubricate, cool, clean, seal, and be a hydraulic fluid.
The hydraulic fluid function, in things like actuators, tensioners, and lifters, is pretty important, and needed at low temperatures too.
So the w number is as important as the grade.
Using 0w30 covers it well.
 
In a two stroke outboard that uses pre mixed oil into the gas you run 50 parts gas to 1 part oil for everyday normal use. 50:1 Pulling skiers and running hard you use 40 parts oil. 40:1 If you ring it’s neck out because you are way under powered or racing high rpm you run 30 to 1 gas oil ratio. 30:1 On engines that internally mix in oil into the fuel line it may go as light as 100:1 if you are at idle or trolling slow. 100:1

In car engines you do the same except instead of increasing oil ratio you change viscosity. Example in my E350 4x4 adventure van pulling the race trailer I’m not running the recommended 5w20 pulling that load thru mountains so I step it up to 5w30 with an extra shot of molly. If you baby your engine with a light load then thin oil lubricates perfect and keeps things clean. If you frequently max it out or pull mountains then go up in viscosity. Pick your viscosity based on how hard you are asking that engine to work.
 
That graph you call the "3 factor bearing graph" is actually called the "Stribeck Curve", and pertains to the lubrication regimes that exists between any two moving parts, not just journal bearings (Google it). Journal bearings behave per and are designed by the Sommerfeld equation, that's where the "bearing charactor number" comes from … it's the Sommerfeld number (Google that too). 😁

This thick vs thin thread has some steam, but I'll say what I end up saying in most of these threads. If the cap says xW-20 or lower, go up a KV100 grade because MOFT headroom is a good thing. Helps keep those top rod bearings and cam chains healthy. Most likely why Ford finally woke up and went from 5W-20 to 5W-30 in the Coyote sold in the USA. It was always speced for 5W-30 in some other counties. Ford trashed CAFE for more engine protection, like it should be. 😀
Sorry I learned alll about this in engineering school. Its for sliding surfaces (including bearings ) as noted.
I won't convince and neither am I trying to ;). I have always known it as 3 factor curve. But yea.
 
What's the definition of "fine"? Not taken back home on a trailer, lol. Guy on YT who tracked his car on the oil cap 5W-20 inspected his rod bearings after a few heavy track sessions and wondered why his journal bearings had so much wear. He thought it was a good idea to run the 5W-20 because he wanted cooler oil temps. 😄 🙃
Do you have a link to this?
 
You brought up a very good point. I was taught not to "lug" an engine, and I always downshift, even with an automatic trans, when going up a hill so the engine can run freely under a lighter load.

I've never examined bearings before, but your suggestion looks and sounds reasonable.
Remember even at a low 1200 rpm speed, a four cylinder engine is firing each cylinder Ten times per second.
That equates to 40 firings a second across all cylinders.
Hardly lugging.

Problem with 4 bangers and their flat cranks, they are firing with all 4 pistons at TDC/BDC. Locked using old steam engine lingo.
Regardless, I have a steep hill to climb in a neighborhood that I used to hit with a cold engine in my commute to work. TCU says 1500 rpm, I knock it back a gear to about 2100 and she seems happier with her 12.5/1 compression and running low octane regular gas!

- Arco
 
What's the definition of "fine"? Not taken back home on a trailer, lol. Guy on YT who tracked his car on the oil cap 5W-20 inspected his rod bearings after a few heavy track sessions and wondered why his journal bearings had so much wear. He thought it was a good idea to run the 5W-20 because he wanted cooler oil temps. 😄 🙃

The GR Supra probably has a good oil cooler, but going up a grade would still add protection.
Why would anyone pull their engine part ot inspect rod bearings after a track day? What was the issue that presented itself afterwards that wasn't there before driving this? You've commented this many times - link for the video for my info? I'll be sure to talk to this guy and send him here for a proper thickie beating ;)
 
I guess I need to explain my post better. Sometimes when dissembling an engine for inspection you will find wear on the upper rod bearing halves(like shown below) and no wear at all on the bottom half. What causes this is during TDC of the power stroke energy travels down the connecting rod to the crank. This squeezes the oil “cushion” between the crank journal and upper rod bearing half. If oil temperatures get to hot and viscosity is to low this cushion could go to zero causing friction and wear. This is common during severe service like racing, towing, plowing etc. and one reason why some manufacturers recommended a higher viscosity in severe service. Something like oil starvation usually causes wear to upper and lower rod bearings.

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Are there times when no discernable wear is found? It seems that even with a well-lubricated, maintained, and operated engine, wear would always occur in that area.
 
Are there times when no discernable wear is found? It seems that even with a well-lubricated, maintained, and operated engine, wear would always occur in that area.
There is always some wear, but it is not normal to wear through layers of a bearing. I’ve inspected many 200k+ mile engines with virtually no visible wear on the bearings. If I measured them I would find some wear. These bearings have allowable tolerances.
 
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In a two stroke outboard that uses pre mixed oil into the gas you run 50 parts gas to 1 part oil for everyday normal use. 50:1 Pulling skiers and running hard you use 40 parts oil. 40:1 If you ring it’s neck out because you are way under powered or racing high rpm you run 30 to 1 gas oil ratio. 30:1 On engines that internally mix in oil into the fuel line it may go as light as 100:1 if you are at idle or trolling slow. 100:1

In car engines you do the same except instead of increasing oil ratio you change viscosity. Example in my E350 4x4 adventure van pulling the race trailer I’m not running the recommended 5w20 pulling that load thru mountains so I step it up to 5w30 with an extra shot of molly. If you baby your engine with a light load then thin oil lubricates perfect and keeps things clean. If you frequently max it out or pull mountains then go up in viscosity. Pick your viscosity based on how hard you are asking that engine to work.
Two stroke oil/fuel ratios have more to do with rpm than load.
I have 3 Husqvarna XP chainsaws and a 35cc weed whacker that run over 10,000 rpm. Same goes for small two stroke dirt bikes, while an outboard boat motor might see 5,500 rpm.
I run the high rpm critters at 28-32:1
 
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It really depends on the engine and the conditions subjected to as to whether it would matter to go up a grade. An increase in headroom is a more sound argument since what harm is there anyway, as others have argued.

Let’s say my personal vehicle (Honda Fit L15A1 engine) with low oil temps and seemingly great UOAs (though not meant to determine absolute wear it’s an okay indication how the engine is treating the oil at least); I’ve never thought it was a need to go up a grade.

However, I did recently (at 320k) because it’s well over 300k miles (just passed 340k) and there is a slow rear main leak. It felt slightly more peppy since upping a grade. But, I also changed to running premium fuel (dealing with emissions passing in my area on an aftermarket CAT) 93 regularly instead of 87. And, I also had a spark plug back out recently, though I was already on 30 grade when that happened, so the oil grade may have nothing to do with it, but I say all of this to say my performance wasn’t worse being thicker one grade. I had other factors to engine running condition than oil grade. Maybe it likes the Amsoil Signature better rather than the grade of oil. 😶‍🌫️🫡

So, what is the harm?

160F peak oil temps
Port fuel injected
70% highway miles
Seldom short tripped
Not severe winters; nor track days…

In this case, the cap recommended 5w20 (before 0w20 was the standard) has likely been sufficient. Though a Honda I4 non-turbo going past 300k miles isn’t remarkable. So, part of me does wonder if I had gone up a grade with long term ownership would I have a slightly less worn engine today? That’s possible though likely not a factor for my engine given the above factors.

A thicker oil grade is recommended in other parts of the world for the same engine. It does lead one to wonder how come that discrepancy? Thus, this whole debate that continues to loop.

So, if a more demanding engine condition and engine design on the oil; comparing manual specs outside of the US? Yeah, I’m down for going up a grade. It’s not going to hurt anything if maybe a slight fuel economy drop. How you drive it will have more impact than a single grade of oil change.

.02
 
Two stroke oil/fuel ratios have more to do with rpm than load.
I have 3 Husqvarna XP chainsaws and a 35cc weed whacker that run over 10,000 rpm. Same goes for small two stroke dirt bikes, while an outboard boat motor might see 5,500 rpm.
I bought a new XP 346 back in the day. It will make even the most experienced chainsaw operators put their saws down and say wow! Honestly one of the best performing fuel operated piece of machinery on earth. Maybe one of Elon‘s rockets would be ahead of it? I doubt it. Nothing does what is supposed to better than a Husqvarna HP.
 
It really depends on the engine and the conditions subjected to as to whether it would matter to go up a grade. An increase in headroom is a more sound argument since what harm is there anyway, as others have argued.

Let’s say my personal vehicle (Honda Fit L15A1 engine) with low oil temps and seemingly great UOAs (though not meant to determine absolute wear it’s an okay indication how the engine is treating the oil at least); I’ve never thought it was a need to go up a grade.

However, I did recently (at 320k) because it’s well over 300k miles (just passed 340k) and there is a slow rear main leak. It felt slightly more peppy since upping a grade. But, I also changed to running premium fuel (dealing with emissions passing in my area on an aftermarket CAT) 93 regularly instead of 87. And, I also had a spark plug back out recently, though I was already on 30 grade when that happened, so the oil grade may have nothing to do with it, but I say all of this to say my performance wasn’t worse being thicker one grade. I had other factors to engine running condition than oil grade. Maybe it likes the Amsoil Signature better rather than the grade of oil. 😶‍🌫️🫡

So, what is the harm?

160F peak oil temps
Port fuel injected
70% highway miles
Seldom short tripped
Not severe winters; nor track days…

In this case, the cap recommended 5w20 (before 0w20 was the standard) has likely been sufficient. Though a Honda I4 non-turbo going past 300k miles isn’t remarkable. So, part of me does wonder if I had gone up a grade with long term ownership would I have a slightly less worn engine today? That’s possible though likely not a factor for my engine given the above factors.

A thicker oil grade is recommended in other parts of the world for the same engine. It does lead one to wonder how come that discrepancy? Thus, this whole debate that continues to loop.

So, if a more demanding engine condition and engine design on the oil; comparing manual specs outside of the US? Yeah, I’m down for going up a grade. It’s not going to hurt anything if maybe a slight fuel economy drop. How you drive it will have more impact than a single grade of oil change.

.02
A friend of mine tracks his Fit. Champcar endurance series. I'm sure they are using a 40 grade but I'll find out....

EDIT: they run M1 5W30 for this...however, for some racing series they run the recommended 0W20! In that series rule state you have to run what the manufacturer calls for so what's on the cap is what they run. Would anyone know? Of course not but rules are rules.

1000028602.webp
 
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A friend of mine tracks his Fit. Champcar endurance series. I'm sure they are using a 40 grade but I'll find out....

EDIT: they run M1 5W30 for this...however, for some racing series they run the recommended 0W20! In that series rule state you have to run what the manufacturer calls for so what's on the cap is what they run. Would anyone know? Of course not but rules are rules.

View attachment 266659
For actual racing, yeah, why run thicker than necessary? If anything the rule is to prevent people from going down in viscosity for extra power at the cost of quicker engine rebuilds.
 
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