"" wrote: > Mike Copeland wrote: > > Recently I had an experienced auto service guy that has > owned his own > > shop for many years tell me that I should not be using 5W-30 > in my > > Silverado as the factory suggests, even though I have 145K > on it with no > > oil related problems. He said that when he does an oil > change he puts > > 20W-50 in all vehicles. I was a little surprised that he > would advise > > contrary to factory recommendations. He showed me an article > from about > > ten ago that said 30W oil does not protect an engine at > normal operating > > temps. This did not seem reasonable to me. If that were the > case I would > > imagine a lot more engine failures would be happening. > > Comments? > > I have a Word .doc with specs which I can't post because they > would be > all over the page. I'll post the text and delete the specs. > If it > sounds interesting enough e-mail me and I'll send you the > .doc. (I got > is some time back from a Ford N/G. I've been using Valvoline > Racing > 20/50 with my 4.6 Ford (T-Bird) and at 140 K it's still > running beautifully. > > Heres the text: > Very few manufactures recommend 10W-40 any more, and some > threaten to > void warranties if it is used. It was not included in this > article for > that reason. 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. > > The Data: > > Listed alphabetically --- indicates the data was not available > > Brand VI Flash Pour %ash %zinc > > 20W-50 > AMSOIL 136 482 -38 Castrol GTX 122 440 -15 .85 .12 > Exxon High Performance 119 419 -13 .70 .11 > Havoline Formula 3 125 465 -30 1.0 --- > > snip / / / / / / / > > All of the oils above meet current SG/CD ratings and all > vehicle > manufacture's warranty requirements in the proper viscosity. > All are > "good enough", but those with the better numbers are icing on > the cake. > > The synthetics offer the only truly significant differences, > due to > their superior high temperature oxidation resistance, high > film > strength, very low tendency to form deposits, stable viscosity > base, and > low temperature flow characteristics. Synthetics are superior > lubricants > compared to traditional petroleum oils. You will have to > decide if their > high cost is justified in your application. > > The extended oil drain intervals given by the vehicle > manufacturers > (typically 7500 miles) and synthetic oil companies (up to > 25,000 miles) > are for what is called normal service. Normal service is > defined as the > engine at normal operating temperature, at highway speeds, and > in a dust > free environment. Stop and go, city driving, trips of less > than 10 > miles, or extreme heat or cold puts the oil change interval > into the > severe service category, which is 3000 miles for most > vehicles. > Synthetics can be run two to three times the mileage of > petroleum oils > with no problems. They do not react to combustion and > combustion > by-products to the extent that the dead dinosaur juice does. > The longer > drain intervals possible help take the bite out of the higher > cost of > the synthetics. If your car or bike is still under warranty > you will > have to stick to the recommended drain intervals. > > These are set for petroleum oils and the manufacturers make no > official > allowance for the use of synthetics. > > Oil additives should not be used. The oil companies have gone > to great > lengths to develop an additive package that meets the > vehicle's > requirements. Some of these additives are synergistic, that is > the > effect of two additives together is greater than the effect of > each > acting separately. If you add anything to the oil you may > upset this > balance and prevent the oil from performing to specification. > > 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.
Nice comment but I believe you left on one important factor about oil viscosity. The lower the rating (ie 10w30 vs 20w50) the less power that is required to shear in it the bearings and from the cylinders walls so the less power in loss. (shearing is normal and not to be confused with film strength or rupture) It is very foolish to use
20w50 in a modern engine unless the temps are above 100F a lot and even then 15w40 is not than enough here. You are not lubing any better than with a good 10w30 oil (actually worse in some ways) and not extending your engines life over a good 10w30 oil. I have seen some engines with a bit of wear actually use more 20w50 oil than 15w40. Also, the reason that Detriot no longer recommands 10w40 because they had a lot of trouble (particularly GM) with teh VI in Dino 10w40 oil cooking out and causing the rings to stick.