Oil Grade Sensitivity

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What gives everyone the idea modern engines are so oil grade sensitive?

General design specs call for them to work from -40 to +122F. At startup temps the difference is beyond huge. While they are liquid cooled you will see a significant difference in operating temps between 5000 lb at -40 on flat ground and 19500 lb at +122F on a 7% Grade regardless. While I can certainly see the argument for 0W-20 at one extreme.and 15W-40 at the other I think the reality is that it is relatively a minor difference when you look at the operating viscosity an engine is designed to deal with.
 
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This:
oil_filler_cap.jpg
 
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What gives everyone the idea modern engines are so oil grade sensitive?

General design specs call for them to work from -40 to +122F. At startup temps the difference is beyond huge. While they are liquid cooled you will see a significant difference in operating temps between 5000 lb at -40 on flat ground and 19500 lb at +122F on a 7% Grade regardless. While I can certainly see the argument for 0W-20 at one extreme.and 15W-40 at the other I think the reality is that it is relatively a minor difference when you look at the operating viscosity an engine is designed to deal with.
The more I read on here, the more I think it just doesn't matter for the vast majority of run of the mill engines.
 
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Idea comes MPG requirements. The graders are specified for best MPG. I just don't see the reliability or performance once the engine develops common problems, that are still too common today. Yes, it tolerates the oil grade for the 'average consumer'.

I prefer to learn from the common and known failure points across various makes/models/engines and adjust intervals, grades, types as needed in a hopeful attempt at failure prevention. I am not sitting around waiting for an automaker or oil acronym(api/ilsac/acea) to come up with a solution during their next update. Gov't and class actions can also be a krapshoot.
 
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manufacturers dont know if you drive at the north pole or the hottest parts of the world + the recommendations used today are for EPA + NOT for long engine life IMO. obviously if your engine barely cranks in the cold oil is too thick BUT as noted on savage geese vid you will never know what damage overly thin oil is doing without an oil temp gauge because that 20W may be a 10W in extreme heat or heavy hauling, NOT a good thing for sure!!
 
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In regards to everyday cookie cutter OEM engines, the main reason is a lack of understanding of oil grades (and oils in general). I see it in car related Facebook groups quite a bit where people say "You can't run 5w-20 in that engine. You need to run a 0w-20. It says so right on the cap."

The reality of common commuter engines is they will spend 95% of their life at <3000 rpm and nowhere near the max load, friction, and heat the engine is capable of. Changes in oil viscosity and additives aren't going to make a whole lot of difference above the minimum spec.

Some race engines can be picky about viscosity. A lot of high rpm naturally aspirated engines with thin (0.7mm) low tension rings, tightly packed on a 1" c/h piston, will be picky about viscosity. They can be sensitive to hydrodynamic friction. I've seen an engine lose >20 hp on the dyno switching from a 0w-5 to a 0w-20 oil, a 4 cSt change in KV100 and 0.6 cP change in HTHS, (operating temp of 130*F) because the increased viscosity and hydrodynamic friction upset the low tension rings at high rpm, causing ring flutter and compromising the seal. That's not a typical application. Definitely an exception, not the norm. The guy switched the oil grades hoping for a little more longevity out of the engine, but lost a good bit of ET (could feel the car nosing over on the top end) and started getting detonation from oil shooting past the unsealed rings into the chamber. Repeating it on the dyno showed why.

Those engines that are sensitive are usually sensitive to any change though as they are very specifically built. I've seen an engine that was dealing with detonation issues and sooty plugs completely solve it by making a small 2 degree change in the floor of the intake port leading into the short radius. The air/fuel mixture was creating a vortex near the plug that was wetting down the plug with big fuel droplets. That simple change pushed that vortex away from the plug and stopped the detonation, as well as picked up power... despite the heads flowing less on the flow bench. I'm getting off a tangent now, sorry.
 

gathermewool

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Agreed, OP. I don’t recall reading about too many oil-related issues that weren‘t one-offs or the fault of the owner. Did I miss something?

In many turbo Subies, the specified 5W-30 shears down to a 20 anyway. It would be interesting to see what a 20 shears down to, if at all.

As far as protection, my FA20DIT-powered Forester is hamstrung by LSPI and deposits concerns. My Legacy is designed and treated such that it will probably run for forever or until it’s HG blows for the umpteenth times (jk!) on any oil.
 
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Oil grades are market specific. Engines can tolerate a huge variety of viscosities.
Mine doesn't seem to care what viscosity I put in it, even with CVVT it still runs the same. Much quieter at high rpm with thicker oil though. I spend a lot of time above 4000 rpm and really beat it so thicker oil is probably a safer bet.

Fuel octane and quality are the only thing that my engine seems finicky about.
 
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I just spent sometime looking at a bunch of toyota vehicles with common engines engines that are in service in the U.S. and other parts of the world.

Every single manual for US vehicles calls for 0w-20 while for other parts of the world all give a range depending on temperature most all engines had 15w-40 as their top tier while some had up to 20w-50.

On top of that on the foreign manuals there was still a warning the even heavier oil may be needed if used for towing and excessive high speed driving.
 
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I remember several years ago, a friend of mine had a Opel Astra 1.4 with the GM Ecotec engine in it that ran like a dream. He was unfortunate too put a 20w-50 oil in it and the engine made lots of valve train noises. He then put in the right spec oil in it, i believe it was a 5W-30 viscosity oil and the engine was smooth as butter again.
 
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Gene K

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On top of that on the foreign manuals there was still a warning the even heavier oil may be needed if used for towing and excessive high speed driving.
That's in Toyota's USA Manuals as well although some believe it's simply in there as part of a simple explanation about different grades and not guidance.

My personal belief is it is intentionally not guidance to avoid any EPA Cafe issues while giving owner's cover if they chose to use a different grade while engaged in an activity resulting in high loads and oil temps.
 
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That's in Toyota's USA Manuals as well although some believe it's simply in there as part of a simple explanation about different grades and not guidance.

My personal belief is it is intentionally not guidance to avoid any EPA Cafe issues while giving owner's cover if they chose to use a different grade while engaged in an activity resulting in high loads and oil temps.
This is why they say to use heavier oil under more severe use conditions.

 
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