I'm sure this issue has come up already, but I am too lazy to find it.
My dealer said I should change the synthetic 0w-20 every 4500 miles. Honestly, I have not reviewed the manual but that seems too soon. As a matter of numbers lets estimate that standard Nissan Altima 2.5L engine can provide an average of 30mpg combined highway + city http://www.fueleconomy.gov/feg/FEG20...neVehicles.pdf, on the NAH we are averaging say 40 mpg. My assumption is that, the 25% better fuel economy is due to the electric motors of the hybrid system. During the driving time that the ice is not "on" I will assume that the oil is not being deteriorated. So if I have driven a total of 4,000 miles, the ice has only been operating for about 3,000 miles, the other 1,000 miles came from the electric motors. My theory is that the actual miles driven are not the actual miles on the ice, so the oil change frequency should be adjusted for such. Any one of you math geniuses out there can please review my theory and my math.

 

This is a very interesting theory, though I think that the percentage the ice is not on is a lot smaller than 25%... For me, the trip computer calculates 39.5mpg when on the highway cruising at 60mph for about 50 miles... During that time the ice is on all the time, and yet the economy is pretty close to 40.

The factor that I am most curious about though is the price difference between regular and synthetic oil vs. the miles you can drive with each before having to change it.
For example, if synthetic oil was twice as expensive, I would expect to be able to go twice as long on it before changing it - otherwise, whats the benefit of using synthetic oil? If it gives me 10% better fuel economy and an extra 2K miles, but I end up paying $30 more for it over regular, in the end it is still a net negative...

 

Don't forget to to factor in the cost of a potential repair if Nissan determines you voided your warrantee by not sticking to their recommended service intervals.

 

You'd have to also calculate the extra strain on the oil from the frequent starts.

Oil changes are cheap insurance against engine damage. If you really want to know what's going on, send a sample of the used oil to Blackstone labs. Then you can start to judge what's really necessary as opposed to someone else's idea of what's right.

 

Ahh, all great points. Me being the busy body I am, I once neglected to change the oil on my Jeep Cherokee, for 23,000 miles. It was still working great when I sold it with 176K milles. My current 4x4 is a toyota tacoma 4cyl. The dealer had a great incentive, free oil changes for life. After the warranty period expired they started scheduling my oil changes to every 10K miles. just something to think about. My current testing of the shell tier 1 gas has not resulted in any significant mpg gains, certainly not worth the .05 per gallon extra cost.
If a synthetic oil lasted twice as long then it would be a benefit because it would save me time from going for service as often. Kind of like to toll reorganization here in jersey.

 

I don't think any of your assumptions are particularly good. Also, the maintenance guide (looking at the PDF right now) basically gives 3750 or 7500 mile oil change intervals depending on whether you're following premium, schedule 1 or schedule 2 intervals.

The Cartalk guys suggest oil changes every 5K miles (every 3K is too often and excessive) now per the URLs below: http://cars.cartalk.com/content/advice/oilchanges.html
http://www.cartalk.com/content/colum...vember/12.html http://www.cartalk.com/content/colum.../March/01.html
http://www.cartalk.com/content/colum.../April/01.html

The 1st URL and http://www.cartalk.com/content/colum...August/05.html talks about what happens to oil in general and how it picks up water and other contaminants.

FWIW, my 06 Prius' schedule dictates 5000 mile oil changes regardless of habits and conditions. Perhaps Toyota is trying to head off the posibility of oil sludging like they experienced on a large # of V6 engines over a wide range of years.

Also, per http://www.fueleconomy.gov/feg/sbs.htm and the MY 08+ test procedure, non-hybrid 08 Altima w/CVT rates at 26 mpg combined and the NAH rates at 34 mpg combined. Another thing of note, I'd imagine the Nissan detuned the 2.5L 4 to produce less power (158 hp vs. 170 or 175), presumably to partly help w/mileage and fuel economy, so that's got to be responsible for some of the mileage improvement.

Also, the CVT in the NAH I'm sure is TOTALLY different from the one in the non-hybrids.

 

I guess my simplistic view and remedial math are just useless and warrant no further thought. Hey!!! maybe filling our gas tanks to half every time may give us better mpg. How much does 20 gallons of fuel weigh anyway?

 

1 Gallon weights ~8lbs. So for every 3 gallons you skimp on, you could improve your MPG by 1%. Hopefully you don't travel out of your way to get gas, because that would likely kill any benefit.

 

If I had a airbag that cost 50% more and protected you better in an accident, would you demand that it be reusable?

Think of synthetic the same way. It costs more and is more protection. Just decide if the extra protection is worth it to you.

 

Everything is subject to the law of diminishing returns. Oil that is twice as expensive does not mean it lasts twice as long, unfortunately.

Incidentally, I have yet to find any dealer that actually has 0w-20. In 20,000 miles averaging 35 MPG, I don't believe my car has ever actually had it.