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I was wondering what weight of oil do you run during the seasons? Do you run 5w30 all year, which some people have told me? Or do you run 10w30 all year, which other people have told me? Or do you do what I do by using 5w30 in the winter and 10w30 in the summer. Or doesn't it matter all together? My manual says that I can run either weight as long as it's 0 degrees and above, anything lower it states to go with 5w30. I don't tow that much or do anything that could get the oil really hot, but I still run 10w30 in the summer regardless.

My oil cap says 5w30 on it though, so does this mean that 5w is best?

 

 

1998 Z71 ext. cab

5.7L

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That just means 5w30 is recommended. It pretty much just gives a broader temperature range, they both turn into 30 anyway, its just the startup thats different!

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It depends on the viscosity of the oil. 5W30 definately has a lower viscosity and pour point in cold conditions compared to the 10w30 (5 vs 10) but interestingly some oils 5w30 actually has a higher viscosity than the 10w30 (meaning more protection from the 5w30 when hot than the 10w30) Here is royal purples oil that shows just that. Each manufacturer could be different though so find their data sheets online.

 

royal purple properties

 

notice on the bottom page that 5w30 has 332 viscosity compared to 360 for 10w30 at 100 degrees (5w30 will pour easier when cold), but at 210 degrees 5w30 is 64 compared to 10w30 63...the 5w30 is thicker when hot. So for this oil, the 5w30 is overall better for protecting when hot and flows faster when cold.

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5W30 will get you very slightly better fuel economy, which is why it is recommended. It is also a lighter viscosity base oil so good for subzero temperatures. I use 5W30 in the winter.

During the rest of the year, I use 10W30. It would be okay to use 5W30, but 5W30 contains more viscosity improvers (polymers), and less VI's are better which makes 10W30 the best choice if the temp never gets below 0.

 

10W40 is rarely ever recommended. I would not use it, and I've read many FAQs that say some automakers actually void the warranty if 10W40 is used. The reason is 10W40 has a lot of VI's to allow it to get to a 40-weight.

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It depends on the viscosity of the oil. 5W30 definately has a lower viscosity and pour point in cold conditions compared to the 10w30 (5 vs 10) but interestingly some oils 5w30 actually has a higher viscosity than the 10w30 (meaning more protection from the 5w30 when hot than the 10w30) Here is royal purples oil that shows just that. Each manufacturer could be different though so find their data sheets online.

 

royal purple properties

 

notice on the bottom page that 5w30 has 332 viscosity compared to 360 for 10w30 at 100 degrees (5w30 will pour easier when cold), but at 210 degrees 5w30 is 64 compared to 10w30 63...the 5w30 is thicker when hot. So for this oil, the 5w30 is overall better for protecting when hot and flows faster when cold.

The viscosity has nothing to do with how well it lubricates or protects your engine.

The only thing the viscosity is important for is how well it flows, so how much and how fast it can get to the parts that need lubricating. So too high of a low temperature viscosity is BAD, and too high of a working temperature viscosity is BAD. (Both stop the oil getting where it's needed).

The factors that make a 'heavier weight' of oil a better lubricant are things like shear strength and film strength etc. These are much more related to the base stock used than to anything else. In simpler times these characteristics were associated with the viscosity of the refined base stock, not as result of it, but associated with it (heavier base stocks tended to also be 'stronger'). That hasn't been true for a long time, because now a whole lot of additives to the base stock modify all the properties of the base stock.

The simple and reliable guide for the consumer is the 'rating' (SE, SF, thru SL etc.) which is a measure of ever increasing performance standards for the resulting oil.

Plus, of course, sticking to your engine makers specs for viscosity.

HTH.

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The manufacturer offers a choice of 5w30 or 10w30 as the poster describes. So you must choose. I have been running the 5w30 mobile 1 year round in my 98 k1500 with the 5.7. No problems. I figured I would follow the cap.

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So too high of a low temperature viscosity is BAD, and too high of a working temperature viscosity is BAD. (Both stop the oil getting where it's needed).

Yeah no kidding, but when the viscosity point number is 1 apart at the hot range, it's not too high. They are both SJ and the 5w30 is thicker than the 10w30 at the hot range by 1 frickin point. Since it's hot and still a fluid it will flow fine and offer better protection...yes even though slightly. You sound like you are talking about liquid concrete that could setup and not flow. When an engine gets too hot, you want something thicker because too thin and you might as well lubricate with water. Shear and film strength are related to viscosity and all give hints on engine protection. If you don't think so...the viscosity of water at 212 is 29.3SSU According to you it should flow better than the two oils listed and with good bond strength should protect better right? NO. My explanation was meant to keep things easy and not get anal about the terms. :P

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So too high of a low temperature viscosity is BAD, and too high of a working temperature viscosity is BAD. (Both stop the oil getting where it's needed).

Yeah no kidding, but when the viscosity point number is 1 apart at the hot range, it's not too high. They are both SJ and the 5w30 is thicker than the 10w30 at the hot range by 1 frickin point. Since it's hot and still a fluid it will flow fine and offer better protection...yes even though slightly. You sound like you are talking about liquid concrete that could setup and not flow. When an engine gets too hot, you want something thicker because too thin and you might as well lubricate with water. Shear and film strength are related to viscosity and all give hints on engine protection. If you don't think so...the viscosity of water at 212 is 29.3SSU According to you it should flow better than the two oils listed and with good bond strength should protect better right? NO. My explanation was meant to keep things easy and not get anal about the terms. :P

The too high of a working viscosity comment was directed (sorry, was intended to be directed) at the idea of using 10W/40, where 10W/30 was recommended.

I wasn't clear, and I accept your point about being too anal about it :cool:

I think we actually agree on keeping it simple, and instead of all the arguing I should have just suggested relying on the manufacturer's recommendation for viscosity and the API rating. :)

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sounds good. I was watching a commercial for a new movie with david spade about getting his childhood back and he was going to jump on a slip and slide and the little girl yells it needs water first. I laughed and thought about this post. :thumbs:

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