Over time, petroleum-based oils will degrade or break down from the heat and pressure inside the engine. As this occurs, the chemical composition of the oil changes and it becomes contaminated. After thousands of miles, petroleum-based oils are unable to protect the engine and must be replaced.

Synthetic oil doesn't contain the naturally occurring chemicals that break down at high temperatures. It is also manufactured without many of the chemical compositions that contribute to oil oxidation and sludge buildup. Synthetic oil can tolerate temperatures that would burn up petroleum-based oils. Synthetic oil is more slippery causing less friction. Less friction and lower temps means more horsepower and torque. See this:

VideoDynoComparison

. with no break in period for bonding, just a warm up!

See the advantages in a pour test comparison at cold temperatures:

VIDEO

starts @ 45 secs in

Since synthetics are more durable, oil changes are not needed as often, and this fact partially negates the cost disadvantage of synthetics. Petroleum-based oils generally require replacement every 3,000 - 5,000 miles ish, depending on service use. Synthetic oils can easily offer double the service life as their chemical composition does not break down over time. Amsoil may go as high as 25,000 miles or 1 year:

VIDEO

Substances like phosphorus and sulfur are general contributors to engine wear. They also harm other parts of a vehicle, such as the catalytic converter and the rest of the exhaust system. By being both more chemically stable under changing conditions and containing fewer undesirable additives, synthetic oil causes fewer problems.
Synthetic oil does not lose its ability to flow well in cold weather, so it is preferred for cars driven in cold climates as start up without oil flow from standard oils causes wear. Synthetic oils also bond to parts better than standard oils giving that extra protection upon start up. Synthetic oils also perform better and more consistently at high temperatures, and so are frequently recommended for high-performance engines.

Disadvantage of Synthetic Oil: 1) Price , 2) Synthetic oil does not hold lead in the suspension of the oil. This is a problem with older car engines that still need leaded gasoline to run in their engines, 3) Synthetic oil is not recommended for rotary type engines.

I would not recommend synthetic oil in a high mileage vehicle as it has the characteristic of flowing easier seeping through your worn valve guides and piston rings.

Myth: “synthetic oil is not suitable for new engines, due to its low friction. This is important for drivers who wish to use synthetic oil on a new car with an engine that according to manufacturer specifications must be "broken in." In cases such as these, the driver should change to synthetic oil only after the vehicle has been broken in using traditional motor oil.” You can start using synthetic oil in new vehicles at any time, even in brand new vehicles. In fact, synthetic oil is original equipment on many brands. There is obviously not much advantage until your first oil change is due. a break in period is not as crucial as it was in the past.

FOR BEST BRANDS AND COMPARISON TEST, SEE POST #3.

 

Synthetic oil is hydrocarbon based. There is no such thing as a "plastic" oil. Oil breaks down over time/use into an acid. The cost is usually negated from a straight hydrocarbon due to the durability of an SHC to last 5 times longer. I have an shc in my tribute as daughter had it for college, and I knew it wouldn't get regular oil changes.

 

BEST BRANDS:

Amsoil OE: Amsoil OE are designed for prolonged oil change breaks. This can be used in 3 viscosities and gives maximum wear and tear protection by lowering breakdown. There are 3 different types such as SAE 10W-30 OE, SAE 5W-30 OE and SAE 5W-20 OE. Amsoil synthetic oils counteract carbon and sludge accumulation as compared to regular oils. Secured with additives for dispersion, Amsoil OE synthetic oil contributes for long life of automobile engine. Amsoil OE reduces energy wastage due to friction, thus delivering improved fuel economy as compared to other conventional motor oils. These help in reducing evaporation and thermal breakdown. Amsoil OE helps in reducing emissions and promote better converter operation. Good video of Oil vrs Synthetic oil:
Mobile 1: This synthetic engine oil is suitable for trucks and cars, especially in the most harsh driving conditions, claims Mobile. It lowers oil breakdown and wear and tear and thus prolongs engine life. It's formulation helps to keep the engine sturdy by minimizing friction. Mobile affirms best performance till up to 15,000 miles. Mobile synthetic oils are available as Mobil 1 V-Twin 20W-50 and Mobil 1 Racing 4T 10W-40.

Pennzoil Platinum: Pennzoil Platinum comes with a limited warranty and helps keeping the engines cleaner as compared to other conventional oils. It reduces sludge formation and cleans approximately 40% sludge after 1st oil change. Pennzoil Platinum is available in different types such as Pennzoil conventional, Pennzoil synthetic blend, Pennzoil full synthetic, Pennzoil high mileage vehicle and Pennzoil ultra synthetic. VIDEO

Redline: Its motor oils are specially designed to provide the highest protection, lowest friction, and exceptional cleanliness for your gasoline, diesel, motorcycle, or marine engine.
I have owned two Subaru WRX's over the past five years and have used many different types of synthetic oils in them. I notice that Redline's oil seems to degrade and burn-off less than other oils...mainly Mobil1. I would recommend this oil to people who drive turbo cars aggressively.
I don't see Redline in the Tests Below, but yes it is good. A Good Video Explaining Viscosity: Joe Gibbs Oil is also Very Good: Video
Edelbrock also has some great oils: EdelbrockOil

The Thin-Film Oxygen Uptake Test evaluates the oxidation stability of lubricating oils. Anti-oxidant breakdown is evident when the oxygen pressure in the vessel rapidly decreases. At this point, the induction time (break point) of the oil is recorded.

The minimum High Temperature/High Shear viscosity for a 30 weight oil is 2.9 cP.

The NOACK Volatility Test determines the evaporation loss of lubricants in high temperature service. A maximum of 15 percent evaporation loss is allowable to meet API SL and ILSAC GF-3 specifications.

The lower a lubricant’s pour point, the better protection it provides in low temperature service.

Total Base Number (TBN) is the measurement of a lubricant’s reserve alkalinity. The higher a motor oil’s TBN, the more effective it is in suspending wear-causing contaminants and reducing the corrosive effects of acids over an extended period of time.

The Cold Crank Simulator Test determines the apparent viscosity of lubricants at low temperatures and high shear rates. Viscosity of lubricants under these conditions is directly related to engine cranking and startability. The lower a lubricant’s cold crank viscosity, the easier an engine will turn over in cold temperatures. 10W motor oils are tested at -25°C and must have a viscosity below 7000 cP to pass.

TEST COMPARISON ALSO DONE ON: http://www.syntheticoilhq.com/comparesyntheticoils.html

Valvoline Syn Power: $49.10 for a 6 pack of 5W30
Redline: $66 for 6 pack of 5W30
Mobile 1: $52.10 for 6 pack of 5W30
Amsoil: $67 for a pack of 6 of 5W30
Pennzoil: $44 for a pack of 6 of 5W30

 

You should only use genuine Mazda oil's in your Mazda.

 

I did say synthetic motor oil is not recommended for rotary engines. It was so much writing, thought i'd mention it again here, thanks.
But i use synthetic in my V6 3.0 ltr engine and in my tranny as well (compatible one).

Idemitsu’s “Genuine Mazda 0W-20 GF-5 with Moly - Synthetic Engine Oil” – ILSAC GF-5 certified now available for Mazda’s SKYACTIV-G gasoline engines available in both the Mazda3 and CX-5. The hyper efficient synthetic oil is engineered to improve Mazda SKYACTIV engine equipped Mazda’s fuel economy and deliver quick starts with fast lubrication for outstanding engine protection even in the coldest of conditions. This new engine oil also meets or exceeds the latest and very tough ILSAC GF-5 requirements. Mazda SAE 0W-20 GF-5 with Moly synthetic motor oil (MAZDA PART Number: 0000-G5-0W20-MQ) is the motor oil Mazda recommends for use in all of its 2.0L SKYACTIV-G engines.

 

To Find out which oils are best for your car (and not just engine oil),
Click on your favorite Brand: Amsoil, Redline, Mobil1, Pennzoil,

Not all have all oils however Amsoil does. Here is the listing for my car:

Engine Oil
Grade 1......SM
Maximum Performance SAE 5W-20 Signature Series 100% Synthetic Motor Oil (ALMQT)
Performance Plus XL 5W-20 Synthetic Motor Oil (XLMQT)
Performance OE 5W20 Synthetic Motor Oil (OEMQT) All TEMPS......5W-20
Manual Transmission,G5M (5-SPD)......GL-5
Above 50 F......80W-90
SAE 80W-90 Synthetic Gear Lube (AGLQT)
SEVERE GEAR 75W-90 Synthetic EP Lubricant (SVGQT)
75W-90 Synthetic Long Life Gear Lube (FGRQT)
Manual Transmission,G5M (5-SPD)......GL-4
Above 50 F......80W-90
Synthetic Manual Transmission and Transaxle Gear Lube (75W-90) API GL-4 (MTGQT)
Manual Transmission,G5M (5-SPD)......GL-5
All TEMPS......75W-90
SEVERE GEAR 75W-90 Synthetic EP Lubricant (SVGQT)
75W-90 Synthetic Long Life Gear Lube (FGRQT)
SAE 80W-90 Synthetic Gear Lube (AGLQT)
Manual Transmission,G5M (5-SPD)......GL-4
All TEMPS......75W-90
Synthetic Manual Transmission and Transaxle Gear Lube (75W-90) API GL-4 (MTGQT)
Automatic Transmission,F21......TIV
Synthetic Multi-Vehicle Automatic Transmission Fluid (ATFQT)
Fluids
Brake Fluid......HB
AMSOIL Brake Fluid DOT-3 (BF3SN)
Clutch Fluid......
No AMSOIL Product Recommendation
Clutch Fluid......HB
AMSOIL Brake Fluid DOT-3 (BF3SN)
Power Steering Fluid......AF3
Synthetic Multi-Vehicle Automatic Transmission Fluid (ATFQT)
Power Steering Fluid......AF3
Torque-Drive Synthetic Transmission Fluid (ATD1G)

 

I'll never use anything but synthetic again. For anyone who lives in a cold winter climate, the sound of your engine at -15 start-up tells you why synthetic is best.

As for cost, it's a wash. I do a full change at 7,000 miles, and at 3,500 I replace the filter and top-off. The higher per-unit cost of synthetic is negated by the longer change intervals. I use Mobil1, and only Wix or NAPA Gold filters. (the NAPA Gold are Wix) I did this same thing on a '92 Integra that was sold at 198,000 miles and still ran like new. This includes puking the radiator and driving 3 miles to home entrusting the Mobil1 to protect me.

I HATE Walmart, but they do have excellent prices on 5 qt jugs of oil, including Mobil1 and other synthetics. Wix filters can be had for a great price on RockAuto.com, and NAPA has decent sales on a regular basis.

 

The price of syn oil here is outrageous!! I try my best to avoid that stuff like the plague, I need it in the 3 to keep the warranty but the 323 runs regular dino oil. Cant afford the synthetic oil with the price its at, they want a minimum of 50 euro/L ($63.87/qt) and that goes up to 140eur/L($178.73/qt) for the "premium" Shell stuff. I just buy the cheap 15euro/L($19.10/qt) unbranded stuff for the 323, last oil change on my 3 was well over 300 euro ($383) and that was for the half-syn half-dino that is the bare minimum for my warranty. sigh.......there are things I miss from the US like cheaper almost everything.

 

I have used Royal Purple and recently Amsoil. I was impressed with Amsoil as it has cleaning additives as well as quiet quick starts, however, i don't drive enough to take advantage of the premium brand. I like to change my oil twice a year so I have just changed to Lucas Oil Synthetic. I only drive 10,000 km/yr.

Oil related problems start with "starting your car". The most wear occurs at initial start up before oil actually hits piston rings. This is where synthetic oil shines as it bonds to metal better and runs thinner upon initial start up getting to those places quicker, minimizing that start up engine wear. Over time the rings will deteriorate to where blow-by may occur leading to engine failure due to: lack of compression, contaminating and blocking the catalytic, and oil getting dirty faster.

 

The difference between racing oil and street oil is largely characterized by the base oil chemistry and various additive packages specified by engine manufacturers. Additive packages contribute multiple levels of lubrication efficiency and protection — including anti-wear, friction reduction, rust and corrosion resistance and detergent and dispersant qualities — that help keep engine internals clean and functioning properly.

“Racing oil is more heavily fortified with additive systems to give the performance to protect the engine,” sums up Mark Negast, technical director at Lucas Oil Products. “Still the same additive systems, just higher concentrations.”

The chemistry restrictions set by API originally targeted only phosphorus — which can be harmful to catalytic converters — and currently stand at 800ppm (parts per million). Phosphorus is typically only found in anti-wear additives, so a restriction on total phosphorus puts a restriction on the total additive.

“ZDDP additives with faster activation rates are more suitable for racing and high performance street engines with challenging friction characteristics, such as flat tappets or new engines undergoing break-in,” says Speed. a ‘60s era muscle car engine with flat tappet lifters requires more ZDDP additives to protect the sliding friction between the lifters and the camshaft than a more modern engine with roller lifters.

“For higher rpm and horsepower, you might see lower concentrations of calcium,” echoes Negast. “Typically what happens is the calcium competes for area surface with the zinc and phosphorus. In NASCAR and IndyCar, you’ll see a reduction in calcium detergents because they’re not necessary. In NHRA, you don’t need detergent at all, just wear protection.”


The new LS30 5W-30 synthetic oil from Joe Gibbs Driven: “It’s one of the first of its kind,” says Lake Speed Jr., a certified lubrication specialist at Joe Gibbs Driven. “It’s developed specially from mPAO base-stock technology that provides a higher viscosity index.” Formulated for high-performance LS engines, the LS30 is rated at 5W-30 but has the effect of higher 15W-40 oil. This oil also has a higher zinc content for anti-wear protection and defends against moisture drawn into the engine by modern ethanol-blended fuels. Other Joe Gibbs Driven formulas are designed specifically for old-school musclecars, air-cooled engines, high-performance Ford modular engines, motorcycles, high-revving imports and marine engines.



Joe Gibbs Driven also offers a full line of engine and vehicle lubricants, including synthetic gear oil, an ultra-lightweight qualifying gear oil, transmission fluids, power-steering fluid, chassis grease, engine break-in oil and engine assembly grease. These base stocks offer a viscosity index about twice that of conventional oil and about 33 percent better than typical synthetics based on regular PAO base stocks. “You can use a lighter fluid yet maintain protection with better efficiency.” Joe Gibbs Driven 75W-110 Gear Oil can reduce operating temperatures in the rear end up to 15 degrees. It can be used in all types rear ends and is available by the case, in 2.5-gallon jugs or 54-gallon drums. The PSF is a full synthetic formula that provides thermal stability to help prevent a pressure drop when temperatures increase. It also offers high-temperature foam resistance for better cooling.