analyzing viscosity of 20 thru 50wt in excel

[1 FMF]

I had posted in "interesting articles" forum about an article in this month's Machinery Lubrication which stated minimum recommended viscosity of journal bearings at operating temperature is 13 cSt.

Let me explain, no there's to much to explain let me sum up, journal bearings are what's in every car engine which the cranshaft rides on, and which caries the brunt of the force from the piston pushing down during the power stroke. So for this argument, these journal bearings are the most important in an engine and common sense tells me would be the most significant source of wear in an engine. We want to minimize wear, therefore we want an oil with minimum viscosity such that the shaft in the journal bearing doesn't shear or break through the oil film.
I think there's more to it than this, so please read journal bearings min recommeded viscosity 13 cSt
to hopefully get the article and get the info for where I'm coming from.

Let's take a conservative approach and say that car engines operate over all conditions, low to high speed. So at low speed < 2000 rpm a high viscosity is desireable to prevent metal-metal contact of rotating parts. And at high speeds > 4000 rpm a low viscosity (shear-stable) oil is desireable becuase of hydrodynamic lubrication and fluid (oil) friction/drag. So what oil do you use?

Someone posted a link to a shell viscosity blend calculator. I used it to create chart above. Debate is open to wether the shell calc is accurate and means anything. I plotted the oils you see listed.

I've read in previous machinery lubrication articles which hinted at optimum oil temp in an engine, although for a natural gas industrial type engine, was 190F. Higher than that resulted in oxidation, and higher temps means higher oxidation obviously. Lower than 190F resulted in nitration, and lower than 160F I think they said was really bad for nitration. This too is up for debate. Is it correct, or at least close? What is optimum oil temp?

What I find interesting is for 5w30, the most recommended oil viscosity, that optimum oil temp of 190F it shows 13 cSt. Coincidence? Conspiracy theory? If I disappear that means CAFE and the EPA got me.

I have an oil temp gauge on my car. With an OEM thermostat of 190 or 195F my oil temps run 190-250F. Coolant temps are almost always < 226F, around 200-220F best I can tell. My experience has been that with 30 weight oils in summer the oil temp has been 220-260+ on average depending on driving conditions. Stop+go traffic and no air through radiator = hot aluminum motor @ > 220+ F coolant temps. Radiator fans come on low speed at 226F and high speed at 234F per my service manual.
Running mobil 5w40 truck/suv currently. Observed oil temps have been 200-240F on average depending on driving conditions. On average, it's been lower than a 30 weight oil, and I seem to notice that oil temp cools quicker now with the 5w40: from 240-250 to 220-230 on average. With the 30 weight it would always stay 230+ always until I shut car off for good amount of time. Also, the 5w40 does not heat up quicker compared to a 30 weight, contrary to what the current belief seems to be.

Back to my chart, I referred to optimum oil temp being 190F, great for 5w-30.
However, my engine and maybe most engines run oil temps at 220+ since thermostats are usually 190F. Can we agree that thermostats are 190F for the reason of lower emissions and greater efficiency?
Then, if oil temps are around 220F normally and min recommended viscosity for journal bearings according to what I think is a reputable source is 13 cSt, then aren't 40 weight oils a good thing? And I mean good thing not as better than 30 weight but as in won't do harm like some people claim since the almighty owner's manual doesn't "recommend" a 40 weight oil. I won't ask about a 50 weight oil, yet.

So here's my thoughts, I've shown hard data, I've said where I've got the number's from and asked if we have consensus on what I think are common understandings. Take my personal experience however. Pick it apart, what do you think? At the least make a good discussion.

> my viscosity #'s for 40C and 100C were taken out of the sticky link at top of this forum, oil technical data. These numbers I got were from the manuf's website and you should be able to verify these as well. These were put into the shell calculator to come up with cSt numbers > 212F (100C).

 

[TxGreaseMonkey]

Interesting material. From my experience, though, I'm less concerned with journal bearings and more concerned with camshaft, valve, and rocker arm wear. This is where wear is usually the greatest, since they are last on the oil line, exhibit the highest pressures in an engine, and are the first to go if there are lubrication problems. It's interesting that 5W-30 fits their position so nicely. It agrees with my experience that most cars today exhibit less wear, perform better, run cooler, and get very good gas mileage with 5W-30. We shouldn't be surprised, though, because most cars are designed to operate with this weight oil in North America.

 

[mechtech]

1 FMF - Thanks for the great chart.
In my decades of auto/bike engine experiences as a mechanic, I've never seen a bearing go south without something else going wrong, and causing it.
[things like a plugged pickup screen, and very low oil]
My father was a mechanical engineer,and said that there is a hydrodynamic film, a wedge of oil, that is like a little oil pump on plain automotive bearings. It compresses and forms a surface that is very tough to break through. Plain bearings should never touch the crank.
A proper feed of oil , at the right location, was critical.
Really, they are made of soft lead, and any touching would wipe them out in a few seconds.
He liked thinner oils for cars.

 

[JohnBrowning]

This is one reason why I am so glad to see 5W40's available from a lot of sources like Amsoil,Redline,Mobil,Delo,Schaffers,Castrol.......I have been saying for well over a year that for 90%+ of N.America a quality 5W40 especialy a true 100% GIV or V is the best year round comprimise. I also think that the fact that most of them provide higher levels of ZDDP or other AW agents is also a plus for them! In this way valvetrains and bearings are all happy.

 

[johnd]

Very good information. All of the sudden I'm feeling a lot better about the 10w30 that I've been using than the 5w30 that I was thinking about changing to since my engine temps are about the same as yours.

 

[Mitch Alsup]

If journal bearings were the source of much of the wear within an engine I would be in good agreement with your conjecture.

However, journals are easily designed (width and diameter) to tollerate rather thin oils. Want to use a thinner oil, widen the journal and reduce the clearances.

Vavle trains can be a completely different story as there are at least 8 different kinds of valve actuation systems, and some are rather tollerant of thin oils, while others are rather intollerant of thin oils.

Say you have a high reving 4-valve engine with direct actuatio of the valve by the cam shaft. If you want to run a thinner oil, here, you hve to make the cam following buckets larger in diameter--but wait, if you did that, there is not enough room between the valves to hold this larger bucket--and the whole top end of the engine has to change to accomodate the thinner oil.

Conversely, a cam-in-block V8 with pushrods, roller tappets and rollerized rockers can already tollerate very thin oils!

 

[427Z06]

Mitch, you summed up my thoughts so well, you didn't leave much for me to add.

Just the same, I still wonder why one of BITOG's staunchest supporters of the concept that UOAs are a valid predictor of engine wear, totally ignores the data and tells everyone that thicker 5w40s are needed to make everyone happy.

 

[JohnBrowning]

Mitch, Your points are well made and support the use of 5W40 from my perspective. A 5W40 is neither too thick or too thin. It is in fact the perfect comprimise. You would be hard pressed to find anything from a 5W20 loveing Honda to a 10W60 loveing European import that could not live a long and healthy life of a GIV or GV 5W40!

You can also only make the bearing jornal so large as RPM become an issue as the jornal gets wider and wider. Wide bearing jornals do not like high rpm's.

Their is enough variation between 5W40's that thick and thin examples of both can be found. We have yet to see a bad report from Delvac-1.

 

[427Z06]

quote:

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Originally posted by JohnBrowning:
We have yet to see a bad report from Delvac-1.

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They're there, just hard to see if you have Delvacitis.

 

[buster]

quote:

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Just the same, I still wonder why one of BITOG's staunchest supporters of the concept that UOAs are a valid predictor of engine wear, totally ignores the data and tells everyone that thicker 5w40s are needed to make everyone happy

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I'll admit it, I'm jumping on the AEHaas/427Z06 bandwagon. I'm now a huge fan of 20wt oils. My car has come to life. I can't stress enough how much better it runs on M1 0w-20. I also trust the engineers that design engines that call for 20wts. On top of that, UOA's have proven that 20wts are excellent. Anything thicker for a daily driver is not necessary.

 

[Gary Allan]

quote:

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I'll admit it, I'm jumping on the AEHaas/427Z06 bandwagon.

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Don't try and hide behind them, Buster!! You've had both feet firmly out of the closet for quite some time on this lightweight thing. You've been

about your lightweight agenda ...

So ..wave your banner high ..don't be an apologist..


Lightweight Pride: Nothing 'gurrrrlyman about it'

I've heard that Anita Briant even drives cars that are spec'd for, and use, 5w-20 weight oils.

All kidding aside ..even many engines spec'd for 30 weight can use it ..and never experience any issues ..seen or unseen. Now a high revving Euro ..a turbo ...a tow vehicle ..sure ..but the average car isn't even driven enough to have it ever reach full temp anyway ..and even if it does ..is it any different than a 30 weight spec'd vehicle occassionally getting a work out?? Probably not. They aren't that far apart. It's just the designation that makes it appear such a radical departure from 30 weight.

quote:

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quote:Originally posted by JohnBrowning:
We have yet to see a bad report from Delvac-1.

They're there, just hard to see if you have Delvacitis.

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Well, you're correct. I myself saw my first D1/TSUV insult event. I was taken back by the thought of such a thing. My champion of all time "The Greatest" of heavywieghts had fallen in the ring. Although it still carried the day ...it was shattering to me.

I have a feeling that the opponent had a roll of nickles in his glove ...or was it Pb

 

[Al]

FME thanks for taking the time and trouble to post this. This chart should be made a sticky somewhere. The discussion resulting is much needed here.

As was mentioned..so many variables in engines, considering design, use, weather, etc. So as usual it gets back to UOA results. There is no question that the 40 weights will act as a buffer in some cases. Personally with my driving style (easy) I prefer to go with the economy of the lighter oils. I have reasonable expectation that in another 100K my engine will still pe performing nicely for someone else.

Again..thanks for taking the time and trouble for this.great job. I'm making this post my enterance to BITOG for my "favotites"