Originally Posted by DiamondStarMonsters

Some things cannot and should not be dumbed down for consumption by the lowest common denominator. Oil is one of them.

Fluid dynamics is not something you can just put in layman's terms and illustrate the mechanics of it in an accurate fashion.

You want an example of how a simple change in oil can create a significant difference in fuel economy and power (which are both related by the way, one often follows the other)

The following was originally intended for one of my boosted gas 2.0L's

There is something called Bearing Operating Condition(BOC) which can be one of 3 states, but you really only want it operating in the 3rd state, fully developed hydrodynamic lubrication. Which correlates to a BOC of 35+. The formula to find BOC is as follows:

BOC = Viscosity x RPM x Diameter x K / Unit Load



Viscosity is in units of absolute viscosity. "K" is a value to convert RPM and Diameter into surface speed. Unit Load is the applied force divided by the projected area of the bearing (the insert width times the journal diameter).

First, viscosity. I can't find absolute/dynamic viscosity numbers for various grades of motor oil, so I took the Kinematic Viscosity of 10w30 (dino) motor oil at 100*C and multiplied it by it's specific gravity. This should give me the Dynamic Viscosity.

Second is the value "K". To find surface speed you multiply circumference by RPM. So Diameter x Pi x RPM = Surface speed, therefore K = Pi Right?

Lastly, unit load. I used 12,000 lbs of force, but this is relative to motoGP/Formula1 type engines, not boosted 4cylinders. I know our engine's see a BMEP nearly twice that of a formula 1 car, so it is a conservative place to start.

I also had no bearings out of the motor to measure their width, so I just put a caliper on the main cap and eyeballed it. I came up with an area of 1.425, so a load value of 8421.

Put it all together, 8.4 x 9500 x 2.245 x 3.1415 / 8421 = 66

The optimal range between 35 and 50 so we are well out of that range.

From here we can use the Stribeck Curve to find our friction coefficient, which I found to be .0057

So with an applied load of 12,000lbs, that gives us a friction load of 68.4 lbs. The diameter of the journal used is 2.245, so 1.1225 x 68.4 = 76.7 in/lbs or 6.39 lb/ft.

At 9500 this equates to 11.56 hp per main bearing.


That is 8600 watts of energy wasted per bearing, and that is only for the 5 main bearings!

That is not accounting for all the rockers, cam journals, cylinder bore contact patches, rod journals or wrist pins. Or the oil pump its self.

So maybe you should bone up on the basics, BC.

What units are used for measuring viscosity?

How does temperature affect viscosity?

What are the real differences between weights of comparable group oils at a given temperature?

These all are key to understanding what the hell I am trying to tell you.

None of this is made up or conventional knowledge. When I tell you something, think about it don't just throw it back in my face or I won't bother explaining it further.

There is method to my madness and I wouldn't be sharing if it didn't have merit for Joe Commuter perusing this board.

If you actually give a damn about learning the science involved for oil go here and read everything two or three times and absorb it:
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Originally Posted by mahout

For those of us engineers who have participated in the development of engines I can assure you that engineers at Honda evaluated 0W-20 oils in the Fit and other engines. Synthetic oils are the choice not only for decreased friction - better mpg - but because of the shear strength. One of the biggest difficulties with conventional hydrocarbon oils is their less resistance to 'shredding' under load pressures, much as happens when you pull a sheet until it tears. In the lubricating process that tearing immediately lets metal to metal contact. And for those of us who have dismantled an engine after wear tests and weighed the moving parts I can assure you that synthetics are much better. In fact, 0W-20 synthetic oil works great while 0W-20 conventional oils are almost certain to fail at load. And 0W-20 is better than 5W-30 conventional oils.

Originally Posted by SilverBullet

Ive been reading about hydrocarbon shearing and its not about shearing as no zddp and the oil thinning out at high heat. If oil shearing is a problem then oil volume is lost. . I do see why synthetics are better but they also get dirty and the oil thins out too and with less zddp there still could be metal to metal contact.

Moly and zddp is the reason no metal to metal contact. Thats why its important to use the MM with the factory fill. Honda uses moly and is one reason Honda engines last so long

Originally Posted by mahout

Oil shear strength varies considerably between hydrocarbon oils and synthetic oils. As temperature rises the oil indeed thins and shear is the result of high loads 'ripping' the thin sheet. When that ripping occurs there will be metal to metal contact. Its not a strict function of the thickness of the oil layer, which I think you equate to volume, but of the strength of the layer itself. A thicker layer of paper will rip faster and under less load than a thinner layer of steel. The analogy isn't perfect but you get the idea.
And because turboed engines develop higher loads on rotating opposing surfaces synthetics are always better. But using synthetics isn't a guarantee of no metal to metal contact, just that it takes longer to get there.

Originally Posted by FIT410S

so today im just had my second oil change at around 8600 miles or 20% on the indicator. btw after the first change i had about 4200 total miles on the car at 20 or 10% indicator, so i went another 4200 or so miles before i got to 20% again and the car felt like it needed the change. i drive mostly short trips in the washington dc area, so that is hard on the car.

i had a mobile filter and mobile 1 syn ex put in for the first change

this time i had a purolator pl14610 ( 5 bucks with free shipping from amazon ) and mobile 1 5w20 ( 24 bucks per gallon walmart) put in.

I seem to notice as the 100% gets lower and lower the car seems to drive rougher below 50% and at 20% I felt it needed the change.

It may just be in my head. but after the change and back to 100% the car seems to drive much smoother. Does anyone else notice this?

note: the mechanic left a small amount in the gallon jug ( feels like 1/2 quart )

Originally Posted by FIT410S

you guys are quite knowledgeable I must say. thanks for the fun reads and help.

what i should of done was check the oil level at 80 60 50 40 20 % and see if the oil level was decreasing.

when i get the oil change thats what it feels like, that there is more oil. i know on my honda civic with synthetic after about 4k miles the oil level went down to about 1/2 on the dip stick.

has anyone been monitoring this as the % in the car goes down?

Originally Posted by Brain Champagne

Which is about two hundred bucks over the life of a car, so the question is does it save enough gas or batteries or wear to make it worthwhile?

I use it, but I figure that at $200 it's pretty much a wash.

Originally Posted by raytseng

It depends on your specific car. some people go the whole distance with absolutely zero oil consumption. Others go from Full to Add over 1 oil change; so just change it at that point and don't add any. Still others consume more and need to top-off a few times in-between.

Most people with the relatively new fit should consume zero or close to zero.

Check after some time to see if you get any consumption. Once you get a feel of it, you can check less frequently or more frequently as needed. Since you are having short trips you may have some fuel or water dilution which throw off the readings. You may want to take your reading only after having a recent freeway trip (at least 10min) to get an accurate reading.

You should note that anywhere between Add and Full is within specification. You don't need to always be at Full.

Originally Posted by jjrbus

Hmmmm

If you can afford it, synthetic is better, I can afford it. But I will not spend the money!!

Truck engines change at 100,000 with synthetic?? Some diesel engines never change the oil!! They have the oil analyzed and put in needed additives.

Testing needs to be done over a period of time to look for changes.

98 Ford 190,000mi cheap oil and filters, still running strong. Oil changed at 3000 Mi when driving around town in summer up to 9000 mi when doing all road mileage.
JIm 0311