I was a factory tech rep for one of the major import manufacturers. Here is the lowdown on synthetic oils from the factory, the techs and the dealers. (A) Synthetic oils are superior to dyno oils in all respects with respect to use in autos and trucks except "break in" and some leak problems listed later. (B) Synthetic blends are an advertising and sales idea. The higher the percentage of synthetic the better, not because synthetics are good, which they are, but because dyno oils are bad for your car. This is true for short trips, long trips, frequent trips and storage. (C) The additives in oils are to offset the potential damage from the dyno oils and combinations of dyno oils and other contaminents such as fuel and water. Where does the gunk, dirt, goo and crap you mentioned come from? The engine crankcases of todays cars are essentially sealed as required by federal law. Therefore, all the mentioned above comes from the breakdown and deterioration of the oil and contaminates which you must expect in a car engine such as fuel and water. Lets not get into "blowby" (D) Mechanics, and I have worked with hundreds (if not thousands) tend to stick with what they know from experience. I wish a few more would try learning for a change. My favorite, and often heard statement from a mechanic is "I've done it that way for years". Unfortunately, my reply is often "Well maybe it is about time to learn how to do it correctly". (E) Oil leaks have occured from Synthetic oils in some of the early cars such as Chevy Vega because incompatible materials were used in the manufacture of the seals. This was when synthetic oils were new. No manufacturer would do that today, but where do your replacement seals come from? (F) Even though engines are now built much better than in the past, the "seating of the piston rings" is still a process of wear. The rings and cylinder walls MUST wear slightly to conform to each other to produce a better seal at a near microscopic level. This "seating" process will be slowed down or even prevented by the use of synthetic oil before the "break in" period. A good reference is 7500 (7.5K) to 10000 (10K) miles, then switch to synthetics. (G) Any oil which meets the minimum rating specs of the car manufacurer will NOT void any part of your warranty. Where the less scrupulous manufacturers will try to void your warranty is if you fail to change oil and filter at the manufacturer's required interval (or miss any other required service). This is in spite of the fact that changing dyno oils at 3K is a good idea but compare to synthetic oils which have a conservative average mileage life of
20K to 25K. (H) Success or failure with synthetics and the inconsistent stories you hear are often due to the MANY unaccounted for conditions of the ownership, manufacture, and use of different cars and brands of cars. For example, synthetic oils can't help much in areas which get little or no lubrication from the engine oil, such as valve guides. Depending on make conditions of different cars, valve guides may wear out at nearly the same mileage, but will probably last longer with synthetic oils since even minimal lubrication depends on the quality of the oil. (I) How many know what 10W30 means? It means the oil acts like 10 weight oil (thin oil) in the cold to help allow the engine to crank over and circulate the oil as soon as possible. Warm 10W30 is 30 weight oil. Cold 10W30 oil is 10 weight oil. Thus 10 W(inter) 30 (Summer) oil rating. Therefore synthetics can drop down to 5W20 oil (saves energy and increases mileage) and still provides better lubrication. Needing 40 weight oil means it is time for an engine rebuild (or you are starving your engine for lubrication and hastening the time it will need rebuilding). (J) Dealers and manufacturers do a lot of things to maintain the customers need for parts and service. Just add up the cost of building a car from a list of the parts making up the car, even without labor. A $20K car can cost $100K if bought part by part. Is parts storage that much more expensive than new car storage? No. (K) Would the dealer like to see you come in for oil and filter every 3K or every 15K (synthetic oil average)? Also true of other service shops who might also catch a brake job or front end work, etc. when you visit.Enough for today. But you get the idea. You are getting what you pay for. How long will you keep the car may be the best guage of which oil to use other than the benefit of cold weather starting and better mileage ( as long as you realize you must drop the weight of the oil). For warranty, check with dealer or manufacturer about weight oil required to maintain warranty. I prefer people do not ask their mechanic. Knowing your warranty is not their job.
RedCrow