This is Part 2 of the oil study:
It is safe to say all modern engine oils are good; the mineral/petroleum oils, the "blended" and of course the synthetic oils. The synthetic oils are without a doubt the best. They do cost more, but they offer more too.
First, lets explain "viscosity" and "grade". Viscosity is a measure of the "flowability" of an oil. More specifically, it is the property of an oil to develope and maintain a certain amount of shearing stress dependent on flow, and then to offer continued resistance to flow. Thicker oils generally have a higher viscosity, and thinner oils a lower viscosity. This is the most important property for an engine. An oil with too low a viscosity can shear and lose film strength at high temperatures. An oil with too high a visosity may not pump to the proper parts at low temperatures and the film may tear at high RPMs.
Explaning the numbers in the data:
"Viscosity Index" (ASTM D-2270) is an imperical number indicating the rate of change in viscosity of an oil within a given temperature range. HIGHER numbers indicate a low change, lower numbers indicate a relatively large change. The HIGHER the number the better. This is one major property of an oil that keeps the bearings happy! These numbers can ONLY be comapred within a viscosity range. It is not an indication of how well the oil resists thermal breakdown.
HT/HS or "High Temperature/High Shear" (ASTM D-4683) is an rating that determines the oils stability in a high temperature, high stress conditions. The oil's ability to withstand shearing and tearing is very important especially in a high RPM engine. The oil's ability to protect bearings, cylinder walls and rings, connecting rod bearings, main bearings, cam lobes and lifters, etc. is vital to an engine. For an oil to pass the ASTM D-4683, an oil must have a protective viscosity of 2.9 cP at 302 degrees F. The HIGHER the number the better!
"Wear" is a "Four Ball Wear Test" (ASTM D-4172 and others) that is used to determine how a particular oil protects aginst surface scaring. Most tests are run using a 40kg weight at 75 degrees C rotating at either 1,200 rpm or 1,800 rpm for 1 hour. The depth of scare produced by this tests determines the oils wear test rating. Unfortunantely, this test procedure is not required of most engine oils today and few producers still use the tests and publish their results. However, Amsoil and Red Line are proud of their "scar" test data and gladly offer it. A few other producers also have the data available for some of their oils. Look for oils that carry a SMALLER scar depth!
"Ash" (ASTM D-874) is the percentage of solid material sulfated ash (by weight) which is left when the oil burns. A high ash content will tend to form more sludge and deposits in the engine. Low ash content also seems to promote long valve life. Look for oils with a LOW ash content. Less than 1% maximum and the lower the better.
"Flash" (ASTM D-92) is the temperature at which an oil gives off vapors that can be ignited with a flame held over the oil. The lower the flash point the greater the tendency for the oil to suffer vaporazation loss at high temperatures and to burn off on hot cylinder walls and pistons. The flash point can be an indicator of the quality of the base stock oil used. The HIGHER the flash point the better! 400 F is the minimum to prevent possible high consumption. The flash points shown in the data are in F.
I could have listed the various oil's zinc content, pour points, pumpability points, evaporation volatility, cold-cranking rating, corrosion fighting qualities, and so on but I felt the main topics were enough to raise an eyebrow.
So much for the data listed. Now for a few other interesting bits of information about engines oils.
Did you know that oil has a Ph? If the Ph is too far out of wack, galvanic corrosion can eat things up! It's no different than a swimming pool's water becoming un-balanced at eating at the metallic parts of the pump, etc. In an engine, there is a microscopic variation of this called "fretting corrosion" that can get to parts that are in contact but move very little under quite a bit of pressure. That is what gives the odd stain patterns on shafts and surfaces that are together a long time. The Ph of the oil is really affected by the water it picks up becvause water will react with gasses to form acids. That is why lots of short trips are bad, lots of blow-by and gasses and lots of moisture that does not have time to be driven out.
Oil starts a bit on the "basic" side and gets more acidic over time. I think they assume that maost cars get a fair number of short trips. This is a bit of a problem for a farm tractor that doesn't get used too much since a "basic" Ph will corrode aluminum and an acid will corrode zinc and iron. Ideally you could keep "half worn" oil all the time but you can't. Maybe this is truly a justification for not changing oil too frequently!
Did you know that an oil's "film strength" refers to the amount of pressure required to force out a film of oil from between two pieces of flat metal? The higher the film strength, the more protection is provided to such parts as piston rings, timing chain, cams, lifters and rocker arms...wherever the lubricate is not under oil-system pressure. Synthetic oils routinely exhibit a nominal film strength of well over 3,000 psi, while petroleum oils average somewhat less tha 500 psi! The result is more protection between between moving parts with synthetic oils versus mineral/petroleum.
Did you know that contrary to what many take for granted, higher viscosity in and of itself does not translate into better engine protection. Extensive testing has shown the opposite to be in fact true. As long as a lower-viscosity oil is formulated to resist evaporation and provide high film strength, this lighter oil will actually deliver ,ore complete protectection to the engine parts, since its more rapid circulation delivers both better lubrication per se, and far better cooling characteristics... a critical advantage, given that oil flow furnishes up to 30% of an engine's cooling requirements. In short, don't be too concerned with the relatively lower viscosity ratings of some synthetic oils. Synthetics are a whole different ball game from yesteryear's petroleums.
Did you know that our engines have temperatures in this range (F)?:
Upper Cylinder Wall 300-500
Exhaust Valve 1200-1500
Piston Crown 700-800
Hydraulic Valve Lifter 250-300
Crankcase 200-300
Top Piston Ring 300-650
Exhaust Gases 500-1000
Combustion Chamber 3000-5000
Coolant Jacket 165-230
Connecting Rod Bearings 200-375
Main Bearings 200-350
Other factors to consider when selecting an oil are the possible use of a light weight fast flowing oil to help prevent dry start-up damage even in warm climates. If you have an oil cooled turbocharger, look for a high flash point oil so coking of the oil will be reduced.
I might add that Red Line Oil Company was the most helpful in finding good quality information. They were also extremely proud of their oils in regard to still being effective at reduced friction (coefficient of friction) even after their oils had been used for 15,000 miles, comparing them to unused oils of other brands. Obviously the used oils had a certain amount of hydrocarbons in them which will cause extra wear. They are also the only oil producer I ran across that tests their oils under moderate loads (40g) and heavy loads (160g) in the wear tests and constantly compare their oils to other brands.
I would also like to say that all the enginners I spoke with at the various companies were more than willing to offer whatever help they could.
In closing I realize a lot of the information is actually too much information but hopefully those who enjoy this type of thing will get something out of it. I know I have. I have learned a lot more than I ever dreamed I would, however I'll be the first to admit, there's much, much more!
Like I said earlier, take this imformation for what's it's worth and good luck in your search for the best oil for your car's engine.....
Bob <font color="1E90FF">/</font><font color="7D26CD">/</font><font color="red">/</font><b><font color="gray">M3</font></b>
The Hammer
Administrator
Let me get this straight... You are swapping out parts designed by hundreds of engineers that get paid thousands of dollars for something you bought at Pep Boys because your buddy who doesn't have a job told you it was 'better'?!?
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