THE FOLLOWING ARE TWO COPY PASTED MATERIALS THAT PROVIDE THE LAY MAN A MORE COMPREHENSIVE UNDERSTANDING ON EVERYTHING ABOUT OIL.
API GL-1 Straight mineral oil
API GL-2 Mild EP for worm gears
API GL-3 Mild EP for spur and spiral bevel gears in axles and transmissions
API GL-4 Medium EP, MIL-L-2105 quality, moderate severity hypoid gears, manual transmissions
API GL-5 High EP, MIL-L-2105D quality, all hypoid axles, some manual transmissions
API GL-6 Extra high EP, now obsolete
Is it important to select the right API GL rating?
Yes. Selecting the correct gear oil performance level will provide the best protection to the components of the transmission.
What do the SAE grades mean?
SAE stands for the Society of Automotive Engineers. The SAE classification system is a way of defining how thin or how thick an oil is. This is known as an oil�s viscosity. The classifications are listed here in order of increasing thickness: SAE 75W, SAE 80W, SAE 85W, SAE 90, SAE 140, SAE 250.
What does EP mean?
EP means extreme pressure and refers to the additive used in gear oils. This additive is designed to stop metal-to-metal contact taking place between transmission components. The EP additives are usually based on sulphur and phosphorous. These elements bond to the metal surfaces where there are points of extreme pressure and temperature, forming a sacrificial chemical layer. The sulphur gives gear oils their characteristic smell.
Will synthetic gear oils and mineral gear oils mix together?
Yes, but beware that there two kinds of synthetic gear available: polyalphaolefin (PAO) based and polyalkylene glycol (PAG) based. PAOs are basically a man made version of mineral oils (although with greatly improved properties) and can therefore be mixed with mineral oils. In fact, semi-synthetic products have mineral and synthetic base fluids in them, so obviously, they must be able to mix. PAGs, on the other hand, will not mix with PAOs or mineral oil. Utmost care must be taken when using this kind of product.
Hypoid is an abbreviation for hypocycloidal and relates to the geometry of the crown wheel and pinion arrangement usually on rear wheel drive cars. The pinion is usually highly offset to reduce propshaft intrusion into the passenger compartment.
Do I need a special oil for limited slip differentials?
Yes. When the power distribution between two drive shafts is no longer equal (usually due to the surface condition that the drive wheels are turning on, i.e. ice, mud), limited slip differentials are able to effectively lock the two half shafts, ensuring equal power distribution once again. When this limited slip differential mechanism �kicks in� there is a high shock loading on the clutch mechanism that requires protection from wear and slippage. Use of the incorrect oil can lead to clutch degradation and vibration.
Why should I choose non-EP straight oils for my classic car?
Depending on the age, make and model non-EP gear oils may be required for use in gearboxes and final drives. Certain designs contained a lot of phosphor-bronze (copper containing) components that are sensitive particularly to the sulphur extreme pressure (EP) additive. The sulphur attacks the copper and destroys the integrity of the meshing gear surfaces.
Is it alright to use ATF in a manual gearbox?
Certain designs do specify the use of an ATF in manual gearboxes, but they should only be used where it is clearly stated by the manufacturer.
Is there one gear oil that will meet all my requirements?
This will depend on makes and models, but very often the answer is no. Gearboxes, final drives, transfer boxes, etc., all have their own specific lubrication requirements. The specification of the oil required will be outlined by the design engineers, who will determine which type of oil will provide the maximum protection to the transmission components. It may certainly be possible to rationalise and reduce the number of lubricants used, but the magical
single product may not be achievable.
What is the difference between a gear oil, an atf and an mtf and why are they sometimes interchangeable?
There is a fair amount of common ground, all do a basically similar job, an ATF could be regarded as a low viscosity gear oil with more precisely controlled frictional properties.
What is an MTF and why is it used instead of a gear oil?
MTF ( manual transmission fluid ) is a term preferred by some OEMs, perhaps they think it's more descriptive than "gear oil". It doesn't call up any particular performance or viscosity. For example a Volvo MTF will not be the same as a Honda MTF.
How do gear oil, atf and mtf viscosities relate to engine oil viscosities?
Gear oils and engine oils are classified by 2 different viscosity grading systems. A 75W-90 gear oil, for example, is about the same viscosity as a 10W-40 engine oil. In theory ATFs and MTFs can be any viscosity as required by the OEM. In practice ATFs are approx. the same viscosity as a SAE 10 engine oil or a ISO 32 hydraulic oil. MTFs are about the same, possibly slightly thicker.*
What is a 75w gear oil as this is only a cold crank rating isn�t it?
The target here is 4.1 cSt minimum @ 100 deg. C + the low temp target. If the gear oil in question is, for example, a 75W-80 it must meet both specs which is effectively the 75W low temp + the high temp targets of both specs.; 4.1 cSt minimum for the SAE 75W and 7.0 - 11.0 cSt for the SAE 80. You can see that the SAE 80 target " overlays" the SAE 75W target so expect the KV 100 of a 75W-80 to be about 9 cSt.
Can one gear oil cover a number of viscosities like 75w-90, 80w-90 and 90 and why?
Yes it can, the viscosity grades are not mutually exclusive, it is possible to blend a gear oil with multigrade characteristics such that it falls within, for example, the SAE 75W and the SAE 90 viscosity bands. A mulitgrade oil ( gear or otherwise ) is simply an oil which falls into more than one viscosity grade.
Why do some synthetic gear oils cause poor shifting in older or high mileage boxes?
If this really happens it can be that the generally lower viscosity of a synthetic gear oil may not suit an older or worn box.
Can engine oils be used in gearboxes if they are the right viscosity and are there advantages to using them?
Engine oils can be used in certain gearboxes, in the past it was the norm to do just that. Modern engine oils can be expected to attain the baseline API GL4 performance required for gear protection. Viscosity is not likely to be an issue, the viscosity of a 10W-40 engine oil, for instance, approximates to a 75W-90 in gear oil terms. The gear oil viscosity grade system uses bigger numbers than the engine oil system but that doesn't mean the oils are thicker.
The advantages?*The detergency and antiwear systems in engine oils may cope with excessive "competition" temperatures better.* Engine oils are intended for a shorter service life than gear oils so one point to be aware of is the viscosity modifiers used in multigrade engine oils may not be as shear stable as true gear oil VM�s so a bigger viscosity drop in service is possible. If you are considering this, use a top quality shear stable engine oil, or talk to us first.
Are filled for life gear oils a gimmick and are they in the long term bad for your gearbox?
I wouldn't say they are a gimmick but they do assume "normal" service conditions. Having a modified engine putting more power through the box & competition conditions don't lend themselves to gentle gear changes so you may see higher wear rates and more wear debris in circulation. It's logical to change the oil periodically if only to flush out the wear debris.
Of course the discerning owner may wish to change the oil occcasionally even if the service conditions are considered to be less severe.
This may raise more questions than it answers but hopefully it is of use to some of you.
THE FOLLOWING IS A COPY PASTED MATERIAL FROM A SITE THAT SUPPORTS AMSOIL - CONSIDERED TO BE THE BEST ENGINE OIL EVER - UNTIL GTO.
Motor Oil Viscosity Grades
What does the SAE Viscosity rating on your Motoroil bottle mean?
How do they come up with this rating . . .really?
When you see a W on a viscosity rating it means that this oil viscosity has been tested at a Coldertemperature. The numbers without the W are all tested at 210° F or 100° C which is considered an approximation of engine operating temperature. In other words, a SAE 30 motor oil is the sameviscosity as a 10w-30 or 5W-30 at 210° (100° C). The difference is when the viscosity is tested at a much colder temperature. For example, a 5W-30 motor oil performs like a SAE 5 motor oil would perform at the cold temperature specified, but still has the SAE 30 viscosity at 210° F (100° C) which is engine operating temperature. This allows the engine to get quick oil flow when it is started cold verses dry running until lubricant either warms up sufficiently or is finally forced through the engine oil system. The advantages of a low W viscosity number is obvious. The quicker the oil flows cold, the less dry running. Less dry running means mu
|Why Does Motor Oil|
Motor Oil Degradation - Why does it happen?
Motoroil chemistry is more complex than you think.
It's All in the Molecules
Synthetic Motor Oils are Superior
Extended Drain Intervals
The Choice is Clear
- How to Read an Oil Bottle - What do those API, SAE and ILSAC Numbers Mean?
- SAE Filtration Study - Better Filtration Reduces Wear and Maintenance Costs
- Motor Oil Viscosity Grades - What do the numbers on motor oil bottles mean?
- Motor Oil Testing Methods - What determines a really good motor oil?
- Change Engine Oil Light - How do these systems work and how good are they?
- Motor Oil Service Ratings - Good information on motor oil service ratings
- Don't Forget The Gear Oil! - Explains Gear Lube technology & maintenance
- Extending Differential Life - Changing differential fluid after break-in extends life
- Drivetrain Service Ratings Explained - Gear Lube service ratings explained
The addition of Pour Point Depressant additives (VI) keep the paraffin in petroleum base oils from coalescing together when temperature drops. Pour Point Depressants can keep an oil fluid in extreme cold temperatures, such as in the arctic regions. We will not go into Pour Point Depressing additives at this time except to say they are only used where temperatures are very extreme to keep the motor oil from becoming completely immobilized by the cold temperature extreme. For now we will just discuss the Viscosity Improvers (VI) additives.
The reason is simple: it would be a SAE 10 motor oil at 210° F! The lower the viscosity, the more wear will inevitably occur. This is why it is best to use the proper oil viscosity recommended by the auto manufacturer as it will protect hot and at cold start ups. Obviously a 10W-10 motor oil won't have the film strength to prevent engine wear at full operating temperature like a 5W-20, 10W-30 or 5W-30 motor oil for example.
Multi-grade motor oils perform a great service not being too thick at cold startup to prevent engine wear by providing more instantaneous oil flow to critical engine parts. However, there is a draw back. These additives shear back in high heat or during high shear force operation and break down causing some sludging. What's worse is once the additive begins to be depleted the motor oil no long resists thinning so now you have a thinner motor oil at 210 degrees. Your 10W-30 motor oil can easily become a 10W-20 or even a SAE 10 (10W-10) motor oil. I don't have to tell you why that is bad. The more VI additives the worse the problem which is why auto manufacturers decided to steer car owners away from motor oils loaded with VI additives like the 10W-40 and 20W-50 viscosities.
Group IV (4) and Group V (5) base oil (synthetics) are chemically made from uniform molecules with no paraffin and don't need Viscosity Additives. However, in recent years Group III (3) based oils have been labeled "synthetic" through a legal loophole. These are petroleum based Group II (2) oils that have had the sulfur refined out making them more pure and longer lasting. Group III (3) "synthetic" motor oils must employ Viscosity Additives being petroleum based.
As more and more large oil companies switched their "synthetic" motor oils to the less expensive/more profitable Group III (3) base stocks it has become much easier to identify which are PAO based true synthetic. Of the large oil companies, only Mobil 1, as of this writing (12-15-2007), is still a PAO based true synthetic. The rest, including Castrol Syntec, have switched to the cheaper/more profitable Group III (3) petroleum based "synthetic" motor oil. AMSOIL Synthetic Motor Oils are PAO based true synthetic motor oils with the exception of the short oil drain XL-7500 synthetic motor oils sold at some Auto Parts Stores and Quick Oil Change Centers. This leaves more than 20 PAO based true synthetic motor oils manufactured and marketed by AMSOIL with only 4 Group III (3) based synthetic motor oils identified by the "XL-7500" product name.