A little quick reading from "this page" found by happening on the same article you quoted from Howstuffworks.com...

10w-30 and 5w-30 will thin at the same rate, but start at a different point, is the way I understood it. I don't think 10w-30 and 5w-30 have the same viscosity at the same temp based on the way I understood it.

yes the 5w means the weight of the oil at i beleive 0 degrees celcius and below and the 30 is the opp temp weight stated right there same article.

It also says the less polymers added to create the range the better, as it'* not the polymers that lubricate, it'* the actual oil itself. So by their logic, 10w-30 is better long term than 5w30... especially if the car calls for 10w-30.

Thinner oil is lower viscosity, thicker oil is higher viscosity. 5W-30 At the thickest is 30 weight and at it'* thinnest is 5 weight.


From Bob the Oil guy'* site.

Oil weight, or viscosity, refers to how thick or thin the oil is. The temperature requirements set for oil by the Society of Automotive Engineers (SAE) is 0 degrees F (low) and 210 degrees F (high).

Oils meeting the SAE'* low temperature requirements have a "W" after the viscosity rating (example: 10W), and oils that meet the high ratings have no letter (example SAE 30). An oil is rated for viscosity by heating it to a specified temperature, and then allowing it to flow out of a specifically sized hole. Its viscosity rating is determined by the length of time it takes to flow out of the hole. If it flows quickly, it gets a low rating. If it flows slowly, it gets a high rating.
Engines need oil that is thin enough for cold starts, and thick enough when the engine is hot. Since oil gets thinner when heated, and thicker when cooled, most of us use what are called multi-grade, or multi-viscosity oils. These oils meet SAE specifications for the low temperature requirements of a light oil and the high temperature requirements of a heavy oil. You will hear them referred to as multi-viscosity, all-season and all-weather oils. An example is a 10W-30 which is commonly found in stores. When choosing oil, always follow the manufacturer'* recommendation.

John is right in saying that 10W-30 should theoretically be better, as it contains fewer polymers than 5W-30. You want to use an oil with the narrowest viscosity range as possible because it will lubricate and cool more effectively than an oil with a wider range.

Correct. But who, if any of us lets our oil go longer than 3000miles or 5000 km and if you do you need your head checked synthetic or not the price of oil is not worth a damaged motor. So when i change my oil my life meter still says aroound 40 % if i remember correctly. And if you live in an area where it could snow as far as into june i dont want to put 10w30 in.

This may be unrelated, but I ran 5w-30 Mobil1 for a couple years after I put in the 160 thermo thinking it would be a good idea since my engine would be cooler. Then my oil pressure got low, then my engine started eating itself...

Just food for thought. I have no proof of what happened to my engine, nor have I torn it apart yet to see what was grinding.

Spend $20 and do an oil analysis and get your money'* worth out of your dino/synthetic oil. Cheap insurance too, to protect your engine.

I'm running 15K on my diesel, at 10K now, and the analysis came back saying I'm good for another 10K.....

Do you take a sample and send off for analysis prior to the change?

No, you just drain the oil, take a sample, send it in, wait for results. That way you know if next time you should go longer or if you should have done it sooner. Usually, you follow the manufacturer'* recommended interval, test that, and if it says you can go further, then you go further. Generally good synthetic, like M1 and PP will be good for at least 7,500 miles, when running dino, 3k is the rule of thumb. But then you've got your Amsoil synthetics that allow you to change your oil every 25k or yearly whichever comes first. To the best of my knowledge, people who have done that 25k usually get very good results.