Motor Oil
 

So when it comes to oil, what kind of an impact do you think each type has?

I know the viscosity is important, but what about other variables such as synthetic vs conventional vs blends? Frequency of changes? engine temps? Brands?

Does the oil have much of an impact on performance or FE?

...basically, "thinner" is better for FE, which gives the edge to synthetics, because their viscosity *stays* more consistant over age and load than dyno-juice does.

...however, dyno-juice *is* less costly, by far. However, more and more of the manufacturers are switching to synthetics for both engine and transmissions.

From my reading I have found this:
Full synthetic beats any other except in price.
full synthetics will cost 2-6 times regular oil (most run $6-9) a quart.
full synthetics can go up to 25,000 miles before changing (with filter changes and top off after 8-10K miles).
Full synthetics help the car start smoother in cold weather. Mine is noticeably better.
Full synthetics offer a more constant performance over their life (will not gum up or degrade as much).
full synthetics can help Fuel Economy what % better, it is hard to tell but my best idea is between .5 and 1%. I have not seen any good ABA testing on this.

Now you can get some of the benefits if you use a blended synthetic oil. the rub here is cost is 2x regular but there is no required level to be called a blended synthetic (or semi synthetic).

In my book if you can shell out the money go for it. It is cheep insurance and may help make it last longer. Will you see MPG gains to off set the cost? No. If you can change at longer intervals then it might be worth it.

Does this cover what you wanted to know?

I use full synthetic oil with a bypass filter. I go 75,000 miles between oil changes.

It doesn't help fuel MPG a bit.

go on.......

A bypass filter removes the small particles that the regular filter can't. That plus full synthetic allows one to go longer between oil changes.

I suspect the FE improvement from running thin oil is so small that you need a really high mpg car to even notice.

What about tranny oil? will synthetic help there?

The way I look at it is that Syn oil is better than Dino oil in the long run. You need to do less oil & filter changes, which means less old oil & filters to be disposed of which is better for the environment. The turning point for me was my wife's car which is a 03 Cooper S, it has a 25,000 km oil change frequency! If its good enough for BMW it works for me. Having said that due to the cars short trips I change the oil & filter once a year and use Castrol Syntec 5w-30.
My own car a 09 Vibe 2.4 stick uses 5w-20 Mobil One and is Changed twice a year, it is supposed to be done every 8,000 km but I go a lot longer than that due to the long Vacation trips we take. I have done this since the first oil change.
My bike which is a 00 W650 uses Kawasaki 10w-40 Syn oil is done once a year just before I put it to bad for the winter. I use the bike for commuting to work which is about 30 km each way.
I just think Syn oil just makes more sense all around.
Neddy.

...FWIW (about 2¢ only), I use synthetic in all of our cars now, but didn't do so originally.

Of course the individual gains of such a mod are small, but it'd be rather foolish not to take advantage of them.
Combine a lot of these small gains, and the total gain becomes considerable.

On the model of car I drive, Volvo went from 5 L/100km in 2005 down to 3.9 L/100km in 2009 (-22%) by using lots of small improvements - thinner engine and transmission oil being one of them.
The cars still look very much the same.

I'm taking advantage of that, and apply the changes to my own car.

Transmission oil is scheduled to be replaced during the next service, so I'll be asking the dealer to put in the newer model's thinner transmission oil and to revert to 0W30 engine oil.