oil for silverado

What year?

Doc

Hey Doc,

Not trying to be a wise guy but would the year make a difference? Wouldn't the same engine for whatever year use the same oil?

V.B.

Pre-Vortec 350 is 10W-30, Vortec 350's take 5W-30.

Doc

Okay. Bearing that in mind, I had the local Chevy dealer do an oil change last time I had it in for warranty work. It's an '03 Silverado

- 4.8L. They used 10W 30. When I questioned them as to why they didn't use the 5W 30 the manual specified, the service manager said they just used whatever they had in bulk. When I pressed him further, he said the only reason the manufacturers were specifying 5W 30 was for slightly better mileage figures and that there was absolutely nothing wrong with running a heavier oil.

Is this bullshit? And if so, would you mind providing me with a little ammo for when I have it in for its 8th warranty service in 24K miles next week?

Thanks.

The same thing happened with my dealer when I went in to get the first oil change for my 4.8L 2004 Silverado. The first dealership oil change if free, but I ended up bringing in 6 quarts of my own Castrol 5W-30. I also had to insist on an AC oil filter, or they would have put in some no-name brand filter stuffed with newspaper. This will likely be the last dealer oil change for me.

The dealership oil change guy basically said that General Motors is totally ignorant when it comes to what oil to put in its engines. This is in spite of the fact that the owner's manual plainly states that

5W-30 is the "recommended" oil and that 10W-30 is only "acceptable" if 5W-30 is not available. (Apparently, 5W-30 is not available at any dealership.) The manual goes on to say, "As shown in the viscosity chart, SAE 5W-30 is best for your vehicle." And the fact that the oil filler cap plainly states "5W-30" didn't impress Mr. Goodwrench. He went on and on about what a horse's ass I was for insisting on using the factory recommended 5W-30 in my truck:

"It doesn't get cold enough around here to require 5W-30."

"5W-30 is just too thin an oil to properly lubricate an engine."

"Some of the dealership mechanics immediately drain the factory-supplied

5W-30 oil from their new cars and trucks and put in 10W-40, 20W-50 etc." -- Apparently, any oil not recommended by General Motors is better than 5W-30.

The fact is that the dealership buys in bulk whatever oil is most commonly used in the area, and that happens to be 10W-30. If they were to stock 5W-30 for the few customers who couldn't be talked into using

10W-30, they would need to spend nearly twice as much buying the 5W-30 by the case, instead of by the barrel.

It has always been my assumption that 5W-30 will provide the best possible lubricating qualities at cold startup, when most engine wear occurs. My feeling is that if I use 5W-30 under low-stress conditions and change the oil and filter every 3000 miles, I will be better off than if I had used 10W-30. You will notice that nowhere in the owner's manual does GM specify how often to change your oil. GM would like you to rely on its Oil Life System which is based on engine revolutions and engine temperature. But this system could let you go on for a over a year without an oil change. Just to be safe, I picked a 3000 mile interval.

There can be problems with all multi-viscosity oils, not just 5W-30, if the oil is put under too much stress and/or it is not changed often enough:

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MULTI-VISCOSITY OILS Multi viscosity oils have polymers 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.

10W-40 and 5W-30 require a lot of polymers (synthetics excluded) to achieve that range. The polymers can shear and burn, forming deposits that can cause ring sticking and other problems. This has caused problems in diesel engines, 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. Follow your manufacturer's recommendations as to which weights are appropriate for your vehicle.

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There are problems with all motor oils, even those expensive synthetics that the dealership would like to sell you:

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ADVANTAGES OF SYNTHETIC OIL Better lubrication properties. Longer intervals between oil changes are possible because synthetics suffer less breakdown due to the better base stock used. Usually the synthetics will have a better additive package, allowing the oil to clean better , pump better at lower temperatures, get to critical areas faster among other things.

DISADVANTAGES OF SYNTHETIC OIL Cost is one big disadvantage. Also, can't really be used in an older engine due to the nature of synthetics, it tends to be a bit thinner at high temperature. This can exacerbate oil leaks and oil burning. Since the oil is more expensive, it makes the leaks/burning more expensive Another disadvantage is that synthetic oil usually is lower in viscosity at low temperatures. It will have a tendency to drain down faster. You may hear your engine more on cold startup.

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The best advice given in the quoted article is, "Changing your oil not only removes the acids and other combustion by-products that have collected in the oil, but it also allows for removal of broken down oil."

thanx folks it helps me alot

martin

Doc,

Those differences in weight always bother me. Except that the 5W30 takes more viscosity improver in conventional oils (something to avoid) I really can't see much difference. When either oil gets to operating temperature they are both the same viscosity. When cooler than 212F they have both have thicker viscositys than when they are hot. So when using synthetics without VI, I really can't see that there would be any difference in lubrication except that the 5W fill flow a little better before the engine warms up.

Another thought. Since the 5W30 does not thin as much between 32F (0C) and

212F (100C), pehaps it thins less than the 10W30 at higher temperatures. That would make it even better.

Leaving town for a couple days but will be back to see if you have any ideas.

My .02

5w-30 has better flow characteristics when cold. Most engine wear takes place on starting when there is little oil in top end. 5w-30 can get there faster than 10w-anything. If you want to put in a pre-lube system that "primes" the engine with oil before starting that would help reduce starting wear. Mike >

I agree. The question is why do many companies specify using 5W30 only when the temperatures are low and using 10W30 when it is hot? In even hot weather the flow of the 5W30 will be better before the oil gets to operatings temperature.

I have my doubts as to whether you could actually measure the difference in flow between 5/30 and 10/30 oil at ambient temps like 25C. And there wouldn't be that much difference at cooler temps either. Certainly not enough to damage an engine. And I'm not talking about Alaska-in-winter type temps.

Ian

Granted. The way the numbers are assigned is that the first number is measured viscosity at 0C and the second number is at 100C. The assigned number is the equivalent viscosity of straight weight oil at those temperatures. Therefore as I see it, when heated 5W30 does not thin as much as 10W30. If that continues as the oil gets hotter than 100C, 5W30 would not get as thin as 10W30.

I just have never been able to find anyone who could tell me why 10W30 should be preferred over 5W30 or even 0W30.

It would seem to me that when ambient temp is above 50F 10w will flow like 5W at ~10F. 10W will always protect better but it has to be able to get there first. Mike

I really can't say what the difference might be. I kind of doubt that there would be that much difference. The point is that all oils thin as they get hot. For example 0W30 at 50F will be thicker than 10W30 at 212F.

When below 100C (212F) which is close to the normal operating temperature the oil is less viscous than either of the oils when cooler. I suppose an ideal oil would have the same viscosity regardless of temperature. Another point is that the thermostat in the coolant is usually about 190F. There are spots in the engine where oil flows that can be a lot hotter than that. I expect perhaps 400F or more in really hard working engines that need synthetics.

The only good reason I can see for using 10W30 over 5W30 or 0W30 is that in conventional oils it has less viscosity improvers (Best to avoid VIs if possible). But synthetics don't usually need VIs so back to my original question, why not use the 0W30 or 5W30 in all weather? If you live in a very cold climate I can't see a reason to switch from 0W30 just because the temperatures are getting high.