-The wider the range of viscosities on the oil, the less durable and resistant it is to 'Viscosity Index Breakdown'. For example, 10W-30 oil does not have as much 'V.I. Improver' as 5W-30, so there are fewer additives to be broken down by the shearing of the engine. In fact, 10W-30 is by far the most 'durable' multi-vis oil there is. You should try to stay away from the wider spreads like 15W-50, 20W-50 and especially the 5W-50.
-Also, thicker is not better, no matter what your mechanic or engineer told you. 20W-50 has 40% more viscosity at operating temperature than 10W-30. This means that your engine has to work 40% harder just to move the oil around inside your engine. An engine with thick 'oil' produces significantly less power, uses more fuel, produces more emissions and runs hotter, all contributing to shorter engine life. A thinner oil can more easily and quickly be 'pumped-up’ to the critical parts of the engine, takes less energy to move it around, helps the engine to produce more power, less emissions, better economy. And the engine will last longer too!
-The first number IS the weight of the oil at cold start-up, so a lower number means a thinner oil that will be pumped up more readily.
-The second number is the viscosity (sic) of the oil once it has reached operating temperature (150 degrees).
-5W-30 or 10W-30 is better in colder climes. By the way, the 'W' does not stand for 'weight', as many erroneously assume. In fact, the 'W' that is in the S.A.E. designation for an oils viscosity stands for 'winter', indicating that the oil will flow at its rated viscosity in 'winter driving conditions'
-Now, the first number in a multi-vis oil describes its viscometrics at cold start-up. (engine off for 4 hours or longer, regardless of the outside ambient temperature)
-The second number describes it performance at operating temperature. This is where a lot of people get confused.
-Here’s a shocker: The actual oil in your engine never wears out! It will always be oil. So additives are a very important part of the oil.
-There are 3 things that make motor oil unfit for continued use in an engine:
1) The additive package becomes depleted and can no longer offer all the performance and wear improvements necessary.
2) The oil becomes overly contaminated with particulate matter, combustion by-products, corrosive acids, dust, dirt, silica (VERY damaging!), and sludge. The sludge is a direct result of the combination of heat, air, water and petroleum (which is chemically the reactive trace elements left in the crude after refining: Sulfur and Phosphorous are the big ones).
3) The oil becomes fuel diluted with raw gasoline. Gas does not lubricate and an oil filter does not filter-out gas. Gas goes right through undeterred. An oil filter is designed to filter out particulate matter only. Cars that are driven mainly in the city with a lot of low-speed driving, a lot of traffic lights, and do a lot of idling tend to put a lot more unburned gas into the oil. It is common for cars to burn a considerable amount of oil because it has become fuel diluted, reducing its ability to lubricate. Then, because the thinned-out oil cannot seal as well, it will let even more unburned fuel and contaminates past the rings, and more of the oil will burn away. The gas being introduced will sometimes take the 'place' of the oil, and when you look on your dipstick, you see that it is 'full'. This will lead some to believe that their car does not burn oil.
-Assuming that you’re rebuilt engine is stock or close to it, I would use a good quality 10W-30 'dino' (conventional) oil until there is about 10-12,000 miles accumulated on the engine.
No matter how well the parts are manufactured the internals of your engine still have a lot of relatively 'rough' friction surfaces when freshly put together. I'm talking about rings, cams, rockers, and bearings...stuff like that. For approximately the first 10-12,000 miles of a fresh engine's life, the parts all go through a combination of physical and molecular changes. First, there is a tremendous amount of friction on these surfaces for the first 12K, and the result is that the parts are reaching what engineers call 'equilibrium'. The parts are wearing into a state of near perfect smoothness, in relation to each other. Much more perfectly smooth than any manufacturer could ever produce. Secondly, as this first 12K elapses the internal parts of the engine are also going through a 'molecular' change. The best hardening processes used by manufacturers cannot achieve what the constant heat and operation of 12K can put the parts through. The parts will become even more hardened, and much more resistant to wear and tear.
-The A.P.I. adopted a classification system to rate the performance of motor oil back in 1961. For gasoline burning engines, it uses letters and the first letter is always an 'S', signifying that it is for 'Service Stations’ (remember those?), assuming that a service station would only be adding oil to gas-burning engines, since no one ever believed there would be diesel powered cars at that time. I always found it easier to think of the 'S' as standing for 'spark ignition', which is how a gas engine works. Anyway, the first letter is 'S', and the second letter denotes the performance characteristics of the oil through the use of additives. 'SA' oil was introduced in 1961. Every time the oils required performance was improved, the second letter was advanced. We are currently at a level of 'SL' for new vehicles sold today. This is a superseding system, meaning that every newer performance-grade oil can be used in any application that called for a lesser grade. e.g...today's 'SL' rated oil can be used in a 1995 vehicle that originally called for an 'SG' rated oil. And that older car will derive extra benefits from the newer oil that were not available when the car was new. However, an older 'SG' rated oil CANNOT be used in today's cars that require an 'SL' rated oil. By the way, it is highly unlikely that anyone would ever be able to accidentally find or buy any outdated motor oil considering that motor oil is a fast moving commodity. It just doesn’t sit on the shelves for too long!
-For all you guys out there that are looking to use some great oil at a great price... :gman: I have a shocker for you: The oil that Wal-Mart sells under their house name (Super-Tech) is very good quality oil. In many tests done over the last year or so, the 'Super-Tech' oil was superior to many name-brand oils. The oil is supplied to Wal-Mart by Pennzoil/Quaker-State. It uses the same high-quality group II/III base stocks as their name oil, but uses an off-the shelf additive package.
The oil companies found out that by adding a small amount of synthetic base stock to conventional 'dino' stock, they were able to significantly increase its cold and hot temperature performance. It approaches full-synthetic performance, but is still a ways away. They are significantly better than regular 'dino'. However, there are still the trace elements in the 'dino' portion of the oil, and that is what contributes to sludge formation. For that reason, I do not use blended oils. Blended oils use anywhere from 2% to 5% synthetic base, depending on viscosity and brand. None are higher than 5%. (Most erroneously assume it is 50/50). This is a BIG moneymaker for the oil companies. :tonka:
In a gearbox such as a differential or a manual transmission, the only type of lubrication that you get is a 'Hydro-Static Boundary Layer', which simply means that there is no mechanical or pressurized mechanism for 'forcing' the lubricant in-between the moving parts.
If there were insufficient boundary layers of lubrication between the gears in a diff or a manual tranny, then the internals of the gearbox would 'weld' themselves together relatively quickly.
So there is a complex group of additives to address just this predicament, and it is called 'E.P'. The additives that make up 'E.P.'(which stands for 'extreme pressure') are developed from zinc, copper, brass, and other chlorinated solvents. These are commonly referred to as the 'yellow metals', and they possess some very desirable properties. They have a very low coefficient of friction, and they tend to 'stay-put', which makes them very resistant to the gearbox's attempts to remove them from contact surfaces through the mechanical shearing action of the component in question.
Basically, no matter how much pressure is applied to these additives, they cannot be 'squeezed' out from between the contact surfaces. This is what allows gear oils to lubricate so effectively without any type of 'Hydro-Dynamic' protection.
This may bring up a couple of questions amongst the more curious: First, if 'E.P.' is that good, how come it isn't put in motor oil to provide even better protection when the engine is first started, or if you were suddenly to lose oil pressure? Great idea, but it can't work for a couple of reasons;
Mostly because it is not legal for the additive to be put in motor oil, because chlorine and any chlorinated solvent or derivative is considered to be a carcinogen, so it can't be in there. The thinking is that a portion will escape to the atmosphere through normal combustion and exhaust, and the government says no!
Transmissions and gearboxes are considered to be 'sealed', so the same rules do not apply.
So, as long as the gear oil you are using is of the correct viscosity range, has the correct EP and LS (limited slip) additives in it, then synthetic is in all respects a better choice than any dino lubricant.
By Kit Sullivan, The Director of Operations & Training and holds a 'Master Tech' certification from 'A.S.E