0-20 and 5-20 Oil, Is It Better?

Low viscosity oil improves fuel economy by reducing resistance inside the engine's crankcase. The ultra thin oil allows the crankshaft and other internal moving parts to move more freely through a fluid mass, just like your spoon will stir coffee easier than honey.

But, does that mean it's better for your engine? That's a debatable issue, especially if you have an engine with some miles on it.

Sure fuel economy will be better but at what cost? You save a few bucks on gas but end up doing a rebuild due to worn bearings and loose rod ends.

The reason mufti viscosity oil was invented was to maximize protection. The thickness, or "viscosity" of the oil changes with engine temperature.

Engine parts expand and contract at surprising measurements. A few thousandths of an inch can make a huge difference on compression and bearing wear. A thicker oil will create a "fluid bearing" under pressure minimizing wear from friction, especially at lower temperatures before the engine warms up.

Manufacturing techniques and tolerances are much more precise these days, allowing for the use of ever thinner oils. And, it makes the fuel economy ratings look better for the manufacturer, in an ever increasing race for maximum fuel efficiency.

So, is using 0-20 or 5-20 right for your vehicle? If it is recommended under the warranty period of 36 to 60 thousand miles I'd say OK, but after that I'd personally go to 5-30 and even 10-30 or 10-40 after 75 to 100 thousand miles respectively on most engines, especially in Domestic V-6's V-8's.

The switch to lower viscosity oils in newer vehicles is primarily fuel mileage driven. Toyota approved its use in some vehicles, but they are not any older than 2003 or so.

http://www.automotiveforums.com/vbulletin/showthread.php?t=604784

I certainly would not recommend changing to a lower viscosity than what is called for in the owner's manual. You would be risking damage due to the oil not being able to maintain its film lubricating properties as well as the materials being used are not engineered for that oil....the tolerances are likely not as tight and thus are more susceptible to the fluid propoerties.

Changing to a higher viscosity oil in a vehicle made for the lower weights can result in starvation of the bearings and lower oil flow rates. Since oil is also used to carry heat away, less oil flowing through means it is having to soak up more heat, which can result in chemical breakdown, sludge, etc.

Changing your driving habits and properly maintaining the vehicle remain the easiest ways to improve your mileage.