homebrewer

Icemark, the 10w-40 and 5w-40 warnings are BULLSHIT.

You cannot make a blanket statement and state that a certain grade of oil has a higher level fo zinc (actually the additive is called ZDDP).

10W-40 and 5W-40 oil made with Group III basestocks have LESS viscosity index improvers than 10W-30 weights made with Group I and II basestocks. The visocity index improvers are thought to be responsible for engine deposits.

Please don't perpetuate the myth of 40 weight multi viscosity oil. It simply isn't true. If it were many OEM manufactuers would not recommend 5w40 oil.

Shoot, Ferrari calls for a Shell 10-60 weight oil in some of their engines. It is very expensive though.

Icemark

No not bullshit at all but proven and posted countless times.

Go get the oil companies own analysis of the oil. You will see that exactly.

Add in the fact that many manufactures specifically call out that your warranty will be voided if you use 10W40 and 10W50 oils in there cars (GM and Toyota for example). But for giggles, tell me even one of the top 5 automotive manufactures to suggest the use of 10W40 or 10W50 oils in their current product.

But (again) lets post up some numbers to prove this (and it sounds like a little education on your part before calling my post bullshit)

Lets start with the basics of oil:

Multi viscosity oils work like this: Polymers are added to a light base (5W, 10W, 20W), which prevent the oil from thinning as much as it warms up. At cold temperatures the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would. The result is that at 100 degrees C the oil has thinned only as much as the higher viscosity number indicates. Another way of looking at multi-vis oils is to think of a 20W-50 as a 20 weight oil that will not thin more than a 50 weight would when hot.

Multi viscosity oils are one of the great improvements in oils, but they should be chosen wisely. Always use a multi grade with the narrowest span of viscosity that is appropriate for the temperatures you are going to encounter. In the winter base your decision on the lowest temperature you will encounter, in the summer, the highest temperature you expect. The polymers can shear and burn forming deposits that can cause ring sticking and other problems. 10W-40 and 5W-30 require a lot of polymers (synthetics excluded) to achieve that range. This has caused problems in diesel and high temp- high rev'ing engines (like our rotarys), but fewer polymers are better for all engines. The wide viscosity range oils, in general, are more prone to viscosity and thermal breakdown due to the high polymer content. It is the oil that lubricates, not the additives. Oils that can do their job with the fewest additives are the best.

Very few manufactures recommend 10W-40 any more, and some threaten to void warranties if it is used. 20W-50 is the same 30 point spread, but because it starts with a heavier base it requires less viscosity index improvers (polymers) to do the job. AMSOIL can formulate their 10W-30 and 15W-40 with no viscosity index improvers but uses some in the 10W-40 and 5W-30. Mobil 1 uses no viscosity improvers in their 5W-30, and I assume the new 10W-30. Follow your manufacturer's recommendations as to which weights are appropriate for your vehicle.

Viscosity Index is an empirical 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 your bearings happy. These numbers can only be compared within a viscosity range. It is not an indication of how well the oil resists thermal breakdown.

Flash point 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 tendency for the oil to suffer vaporization 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 used. The higher the flash point the better. 400 F is the minimum to prevent possible high consumption. Flash point is in degrees F.

Pour point is 5 degrees F above the point at which a chilled oil shows no movement at the surface for 5 seconds when inclined. This measurement is especially important for oils used in the winter. A borderline pumping temperature is given by some manufacturers. This is the temperature at which the oil will pump and maintain adequate oil pressure. This was not given by a lot of the manufacturers, but seems to be about 20 degrees F above the pour point. The lower the pour point the better. Pour point is in degrees F.

% sulfated ash is how much solid material 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. For high rev'ing engines, rotaries, and two strokes, you want oils with a low ash content.

% zinc is the amount of zinc used as an extreme pressure, anti- wear additive. The zinc is only used when there is actual metal to metal contact in the engine. Hopefully the oil will do its job and this will rarely occur, but if it does, the zinc compounds react with the metal to prevent scuffing and wear. A level of .11% is enough to protect an automobile engine for the extended oil drain interval, under normal use. Those of you with high revving, air cooled motorcycles or turbo charged cars or bikes might want to look at the oils with the higher zinc content. More doesn't give you better protection, it gives you longer protection if the rate of metal to metal contact is abnormally high. High zinc content can lead to deposit formation and plug fouling.

So now that you (and the other readers understand a little more about the basics of oil- for about the 20th time this is posted), lets look at some numbers:

Brand VI Flash Pour %ash %zinc

20W-50
AMSOIL 136 482 -38 <.5 ---
Castrol GTX 122 440 -15 .85 .12

5W-50
Castrol Syntec 180 437 -45 1.2 .10 (and .095 % Phosphor:O )
Quaker State Synquest 173 457 .76 --- .14

5W-40
Havoline 170 450 -40 1.4 .16

10W-30
AMSOIL 142 480 -70 <.5 ---
Castrol GTX 140 415 -33 .85 .12
Red Line 139 475 -40 --- ---
Valvoline Turbo 135 410 -26 .99 .13
Valvoline Race 130 410 -26 1.2 .20
Valvoline Synthetic 140 450 -40 1.5 .12

5W-30
AMSOIL 168 480 -76 <.5 ---
Castrol GTX 156 400 -35 .80 .12


See those numbers back up what I am saying.

But remember the numbers above are not, by any means, all there is to determining what makes a top quality oil. The exact base stock used, the type, quality, and quantity of additives used are very important. The given data combined with the manufacturer's claims, your personal experience, and the reputation of the oil among others who use it should help you make an informed choice.