OK -I found some of the info I was talking about (from Americas car show.com): Please note a few things that are mentioned that I have found numerous other sources to be contrary to the following;
"Longer change intervals: 5,000 - 7,000 miles between oil changes"
..Ua, ya -GM oil life can go up to (in my last oil change in my 04" Yukon) almost 9,000 miles. 5,000 - 7,000 would be on the low side.
"nor do I recommend using it in new engines during the break-in period"
This has been brought up more than a several times on this and many other auto sites I have seen or been a member of. The bottom line: using syn during "break-in" is fine. The only thing, which I know is true (I'll tell you in a minute) and is said here as well, is a longer break-in period. My 04 Yukon (using Mobile 1 syn. since its first oil change at 1500 miles) did not break-in until about 14,000 miles. I know this because I was on a cross county trip getting about 16 MPH on the HWY and 14 in town. After that I now get 17.2-17.8 MPG town and 19.5 HWY (4.8 liter). This was also the case in 2 other cars I had in the past that I ran syn. in.
All engines will eventually break-in; just takes longer running synthetic.
Plus -what about the cars that come with and recommend synthetic? -- What you dont use synthetic until XXXX miles?! -Come-on. Its fine even for break-in.
"It flows easier in cold weather, therefore no loss of prime when the oil is cold. "
True. Also he fails to state that it flows "easiest" in the heat. I go against manuf. recommendations on both my vehicles that "recommend" 5W 30 oil weight. I live in Arizona. I use and have always used 10W 30..... a little more weight for us here in the 110 degree days helps. So all of you in the hot climate should also consider going up to a 10W if running a 5W now.
Anyway, enuff about me
here it is:
Should I use synthetic oil in my car?
That depends on the vehicle's age, mileage, and the carmaker's recommendations for engine lubricants. Older vehicles with high mileage tend to have excessive mechanical wear in the engine, allowing for internal oil leakage. On vehicles with high mileage, it is not recommended to use full synthetic oil because it is thin and very free flowing, and use of it does (more often than not) result in internal oil combustion. I used full synthetic oil in a Plymouth Neon. After logging120K miles the car started to consume oil at an alarming rate. Concerned, I switched to a semi-synthetic oil that was more full-bodied and the consumption stopped. I logged another 30K miles and sold it. It's still running with over 200K miles today and it doesn't burn oil. Carmakers use full synthetics and semi synthetics in some of their engines today. In most cases, you will find that a synthetic lubricant is used when there's a high performance engine with tight engine tolerances, high compression, and high operating temperatures. Follow your owner's manual for motor oil recommendations. If you want to use synthetic oil and your car is still under warranty, check with your local dealer before switching to synthetic oil (just to make sure you're covered with the switch).
Does it work better in some cars than others?
As I stated earlier, some carmakers recommend only using synthetic oil in their engines. For instance, Chevy recommends the use of Mobil One full synthetic oil in its new generation Chevy Corvette engine. I have used synthetic oil in all of my vehicles for the last six years with great results, with one exception. I didn't use a full synthetic in my Ford Taurus 3.0 DOHC V-6. Ford specifies using a 5W20 semi synthetic due to engine design, so I followed the manufacturer's specification. Remember, before changing to synthetic oil, check with your dealer on carmaker's recommendations. As stated earlier, you could void the warranty.
What are the pros and cons of using synthetic oil in my car?
It flows easier in cold weather, therefore no loss of prime when the oil is cold. Also, it is highly resistant to viscosity breakdown (the ability of the oil to flow easily in all temps) from heat, friction, chemical contaminants.
Longer change intervals: 5,000 - 7,000 miles between oil changes (compared to 3,000 for regular oil). Some folks have documented up to 25K miles between changes. However, I would not advice going that long!
Cost is twice as much as conventional oil per quart. However it lasts longer, so the actual cost increase is closer to 50 - 60 percent.
Flows easily, therefore not recommend for use on high mileage engines; nor do I recommend using it in new engines during the break-in period because it is so slippery and dramatically limits the wearing of new mating parts within the engine. This initial wearing of parts is what makes for proper engine break-in, sealing of piston rings, mating of camshafts and lifters, etc.
Does it make my engine last longer?
Yes, because its so slippery, synthetic makes for less engine wear and thus greater engine longevity.