How much does the grade of oil you use affect your gas mileage?

Whenever I get my oil change, this question comes up. Is the expensive sythetic oil worth it? What benefits does it have, both for your gas mileage and your engine? Is it worth paying $25 bucks more an oil change to get it?How much does the grade of oil you use affect your gas mileage?
Motor oil does three things for your engine. It lubricates the engines moving parts, carries away impurities, and it cools the bottom end of your engine. With age the oil breaks down and becomes thick and doesn't flow properly. This causes your engine to build up heat causing friction which causes more heat and more friction, causing wear. Conventional motor oils are good for a maximume of 4500 miles before it breaks down to the point where it's additive pachage is gone, the flow characteristics are destroyed, and the acids and adverse chemicals your engine has produced, due to the internal combustion of fuel, has turned it into a useless goo. Synthetic oils do not break down like conventional oils, so they stay viscouse for much longer. They will lubricate your engine much longer and cool it longer then conventional oils. They also carry away impurities, so, even though they cool and lubricate your engine for a longer period of time, they are still building up acids, and such, that can corrode the internal parts. You can use synthetic oils over conventional oils, but you shouldn't leave them in your engine for over 5000 miles between oil changes. You can change from conventional to synthetics at any time with no adverse effects on your engine. Changing types at high mileage is fine also. Just keep in mind there is a break in period. The conventional oils have built up glazes which help old seals from allowing oil to leak. Synthetic oils clean away the glaze, but soften the seals so they stop oil from leaking. There is an interum period where the glaze has gone but the seals aren't softened completly where the engine leaks oil. This will disappear over time. Due to the increased oil flow and damaging coatings removed, the friction inside the engine should lessen, so the mileage should improve slightly. I read a test where a Dodge Dakota's lubricants were all changed to synthetics. The truck was dynoed before and after the change. There was a 7% increase in horsepower.
I am a strong believer in the synthetic oil. I use Amsoil all the time and it costs double or more than regular oil. Amsoil is great, see this link:

http://www.amsoil.com



also, use the proper type; i.e. 10w30 or 10w40 or 5w30 or 5w40 as specified in your owners manual as to not void the warranty. never use straight 30w for example or 20w. those are for mowers and other weird things.



Synthetic BLEND should be used if you never used synthetic before and you have over 30000 miles on your car because it is too late to use all synthetic (thinner and will leak).How much does the grade of oil you use affect your gas mileage?
It's a waste of money. Modern oils are good for up to 10,000 miles. As far as gas consumption goes, it's the viscosity of the oil that effects mileage, not the type.
Affecting gas mileage? Very little. A synthetic will remain liquid at a larger range of temperatures and, will reduce wear on components.



For me, the gain in using synthetic is that I'm NOT using dinosaur oil. I'm helping to create a market for something other than crude oil. It's not much, but it's something I can do.



If you're going to keep your car for 200,000 miles, I don't think there's any difference in engine wear. If you want to keep it forever and put a zillion miles on it, then switch to synthetic.



Oh, synthetic will not 'gum' up... so if you switch, do it slowly. Like put in 1 quart for an oil change, then 2 the next oil change...How much does the grade of oil you use affect your gas mileage?
Rule 1: Always use the correct weight in motor oil as stated in your owners manual



Rule 2: If your car has some serious miles on it DO NOT switch to synthetics.



Why??? Well, synthetic motor oil not only lubicates better at high temps - it also "Digests" build-ups in your engine. If you have high miles on your car these gunky build-ups are probably plugging some teeny, tiny holes in your gaskets etc... and once you run the synths for a while you will develop leaks.



If you are looking to extend your gas mileage and/or reduce emissions you would probably do better with a high quality fuel additive. The one I use has boosted my mileage by 20% (Subaru outback wagon, 2.5 turbo) and allowed me to switch from premium fuels to mid-grade with no loss in power and no knocking. I won't advertise here but I do have a link on my profile if you are interested.