First of all, you must Understand that the Engine Oils, Basically Does all these Things:
First: Engine Oil stops all the Metal surfaces in your Engine from Grinding together and Tearing themselves apart from Friction, by Lubricating its internals.
Second: Engine Oil transferes the Heat away from the Combustion cycle.
Third: Engine Oil must also be able to Hold in Suspension all the Nasty by-products of combustion, such as Silica (silicon oxide) and Acids, also External contamination, such as Dust.
Fourth: Engine Oil minimises the Exposure to Oxygen and thus Oxidation at Higher temperatures.
It does all of these things under Tremendous Heat and Pressure...
Part one: the Proper Viscosity (SAE Grade) Recommended for your engine.
Remember that Those oils with a "W" on their SAE Grade, are "Multigrade" Oils, (W for Winter times) which means that the Oil will be as Thin as the First Number on their SAE Grade when the Engine is Cool (to aid a Faster and proper oil Flow when you First start the Engine); and will become as Thick as the Second Number on their SAE Grade when the engine Reaches its Normal operating Temperatures.
In example: a 20W~50 Oil Will be 20 when Cool and Gradually will become thicker as temperature Raises, so after some minutes Running inside the Engine, that Oil will become 30, then 40... and the Peak number is 50; usually only reached at Normal Driving Temps, but it might Vary, depending on how Hot the operating temps are on each engine.
That Happens since Polymers where added to the Oil and Those absorb temperatures... also a Thinner Oil will increase the Oil's Pressure and that is really needed on Cold Starts, to help the Oil to Reach the Farther engine's places Faster.
A Monograde Oil (Single SAE Number) will not vary at all and will keep its Thickness Number Permanently, unless it becomes Very hot, when its Thickness 'Could be' Reduced, it is known as "Oil Break Down"... (Specially on Cheap brands with poor Quality) ...That is the inverse situation and could be Harmful for a Very Hot Operating or for an Overheating Engine: That oil under that conditions could Lost its main Lubricating Properties. :-\
I Really advice against the use of Monograde oils on Cars, because they Won't flow properly on Cold Starts and remember: Those parts that worns faster inside the Engine are those parts that doesn't get Oil fast enough with Proper Pressure; so a Multigrade Oil will Reduce both the Time working without Oil on Cold Starts and the low Pressure. :cool:
Monograde oils could still be good for Power Plants, 18 wheels' trucks, etc... But Not ideal for a Car's engine.
Keep the Proper SAE Grade in Mind when you Buy your Next Oil.
Part Two: The Motor Oil's Quality.
The American Petroleum institute (API) Has Two ways to classify Motor Oils: the Gasoline Motor Oils are clasified under the "S" Letter (From "Spark" combustion engine) While Diesel engine oil is clasified under the "C" Letter (From "Compresor" Combustion engine)
The API has a program to certify that the Motor oils, meets the strict Performance and quality standards put in place by the OEM. The Service Rating is shown in the API “Service Seal” on the product label, that may look like one of these examples:
So, The letter that follows the "S" or the "C" will let you know if the Additives Package (Detergents, Dispersants, Stabilizers, etc... ) is Better or Worse for your application.
Any Letter from "A" to "Z" could be next to the "S" or "C" Letter, the more Newer Classification will place a Newer Letter there, as Follows:
- SA = Early -older- motor Oils, Very Basic and without any Additive.
- SL = Very Recent Classification, includes a Complete Additive Package for Gasoline Engines under the APi Norm.
- CF = -or any other Letter instead the "F" like "H", etc.- (Could have a Number 2 or 4 Next to it) The CF or CF4 are for Normal (four Stroke) Diesel engines, while CF2 oils are for Two Stroke engines.
I've used Diesel oil on Gasoline engines for Years, with Great Results; if you want to do so, you should check if that Diesel Oil carry the Additives Package for gasoline engines too, if not, AVOID use it.
I Kindly Suggest you to Check ANY Motor oil to see if it has the Round Seal from the API ... as the above posted Examples.
And the Proper SAE Grade inside that Seal's Circle.
If you Pour a "Diesel Only" Oil in a Gasoline Engine, it could be somehow Harmful for the Engine in certain way... While the Diesel Oils with gasoline Additives Pack included, are Very Good and Outstanding Oils for Gasoline Engines.
On the Other Hand: if you Pour just "Gasoline" Non-diesel motor oil on a Diesel engine, the Oil will be Blackened almost inmediately and will fail for Proper Lubrication and Protection of the Metallic Surfaces, Beside other malfunctions; because the Gasoline oil will absorb the Harmful particles that Diesel Combustion filter to the oil and it couldn't manage that because Gasoline Motor Oils aren't intended for such contamination.
The newest Service category Rating for Gasoline engines in 2012 model year cars and light trucks is “SN.”
The API SN rating is equivalent to the new GF-5 oil rating by the International Lubricant Standardization and Approval Committee (ILSAC).
The new SN and GF-5 rated motor oils are backward compatible and can be used in any older engines.
For Diesel engines, The current category is “CJ-4” (introduced in 2007 for newer diesels that have exhaust gas recirculation). The previous CI-4 (2002), CH-4 (1998) CG-4 (1995) and CF-4 (1990) categories all can be used in older four-stroke diesel engines. CF-2 (1994) is the API classification for two-stroke Diesels.
Part Three: Synthetic Motor Oils.
Synthetic Motor Oil... It's a confusing topic, and there's a lot of Rhetoric, largely Because some Manufacturers and Peddlers of Synthetics have made a lot of inaccurate and self-serving claims over the years. Some, actually a lot, of this Rhetoric is pretty Strident and Opinionated.
The problem that Most People encounter when switching a High Mileage car to Synthetic Oils, is due to the Detergents in the synthetic oil.
The conventional oil "Gunk" accumulates Around the Gaskets and other Places, often times preventing leaks... The Synthetic oil begins to Remove this "Gunk" and things like Oil Pan Gaskets, Main Seals, and Valve Cover Gaskets, start to Leak oil.
Now there are "High Mileage" Syntetic motor oils, so the Leakage problem could be, somehow, controlled ... ...
But another thing to Consider is, Based on your Car's year model and type of cam/lifter configuration... a Roller Cam system works fine with Synthetic oil; However, with the removal of Zinc from Engine Oils over the last few years, many Flat Tappet Cams have been unhappy with this change.
Most Synthetic oils Doesn't contain Enough Zinc and are Not additive friendly ... ...
Briefly, there are Two Types of "synthetic" Oils on the market.
Group IV oils consist of Molecules that are synthesized from simpler chemical compounds. This lets the Chemical Engineers to "tune" the characteristics of a lubricant to exact specifications.
These oils are "Fully Syntetic" and flows more Freely at extreme Low temperatures and don't Break Down at very High temperatures; also they generally can be specified one or two grades Lighter than a mineral oil, which consumes less energy and saves Fuel. (Energy Conserving Oils)
Group III Oils are made from Reprocessed petroleum products normally left over after making Crude oil into Gasoline, Diesel fuel, Heating oil and other products... so they're "Half Syntetic" oils, or Syntetic Blends.
They're more modestly priced and have many of the desirable characteristics of the higher-priced Spread. In much of the World outside the USA, Group III-based lubricants are not allowed to be marketed as "synthetic."
Don't assume that if is a Synthetic Oil, it is so Good... (Read: very Expensive) ...that you don't need to Change it as often. The base lubricant may be way Better, but the Additive package... (which can be as Much as 25 percent of the Volume of the Product in a Bottle) ...can still Become Exhausted.
Also: Unburned Fuel, Partially Burned Hydrocarbons, Atmospheric Dirt, Metal Wear Particles and Blowby Carbon Particles will Build Up just as fast in a Synthetic-Lubricated engine as in one with petroleum-based oil ... ...
The Only Way to Remove this stuff is to Drain and Replace the oil.
I've always recommended 3000-Mile oil Change intervals.
So, with that facts in Mind, To switch to Syntetic motor oils on older engines intended for the Average Driving needs, does Not make any sense; Those syntetic oils are Better for Newer engines... (with Closer tolerances and better PCV systems which keep their oils Cleaner) ...or when the Car is build for Race or Special purposses; but otherwise you'll be Wasting a lot of Money unnecesary, because you'll need to Drain the Oil every 3000 Miles to keep the Oil with proper Lubrication and the Engine internals safely clean.
Part Four: Motor Oil Flush.
I Suggest to use a Motor Oil Flush Cleaner Detergent at least once per Year. I Use it Two or three Times per Year on my BumbleBeast's Weberized EA82 because I Drive it very Hard, 40% off-Roading (on weekends) and 60% in City Streets. (is my Daily Driver).
It is Amazing how many Mud and Dirt those Cleaners Remove from the Engine... You just need to pour a Bottle to the Old oil Just before changing it, and let the engine idle for ten Minutes... (Follow the Directions on the Motor Flush Bottle, it might vary on Different Brands) ...then Flush the old Oil and Voilá!
I Hope this will Help, because Motor oils Shall not be Choosen by Brand or Marketing, but by the API Classification and SAE Grade considering the Specific Application where they're Needed.
I Found an important Document which have a Professional Oil Test, done between the Different oil Brands and between Petroleum Based Oils and Synthetic Oils; they compare the Wear that leaves after the Test on a Metallic Surface, using each Brand of Oil; it has Pictures, so you can Easily "See" which oil is Worse and which oil is Better to suit your Needs.
You can Download the Document, a .pdf File with less than 5 Mb, ~► Here.
Edited by Loyale 2.7 Turbo, 03 March 2012 - 12:21 AM.
To add the Download Link ;)