I'd like to start out by saying I'm new to the board. I appreciate the fact that opinions will be varied on this topic (I just searched synthetic on the forum and read 250 threads that mention the word). I pre-empt this thread that while I am not an engineer, professional / hardcore racer / or employed as a mechanic, I have done alot of tinkering with cars, trucks, tractors, etc. With all I have read, seen, and heard I can't get definative answers to the following:

Are all motors in passenger cars run at the assembly plant or in the car / truck before they arrive in a dealership? Having been to a caterpillar tractor plant the motors are started (with natural gas!) & run for the amount of time it takes to start them & blip the throttle twice. They are then shut down and installed in the equipment... no break-in.

Does anyone know for how long? The company I work for is an OEM of large Refrigeration Compressors (5-160 tons) and from what I've seen in our testing it takes at least 45 minutes for a cast iron block to reach a uniform temperature.

If all motors are not broken in, how about high performance engines (LS1 / LS6)? Is the engine oil changed prior to sending the cars out to remove metal fragments?

Again, how long does these engines run for? I can't imagine that running for less than 4-5 hours would be of any value.

I ask the above to get to the following: It has been stated that engines coming from the factory with non-synthetic oils should be run for certain amount of miles (varies from 300 to 3000 depending on who you speak with and read) before switching over to synthetic oils. My question is why run conventional oil at all? Is there a legit reason for this that doesn't start out with "in my opinion....", I'd much prefer someone who could explain "from my experience"? Todays automotive parts are machined to such exacting specifications (fractions of a thousanth of an inch) that there doesn't seem to be a real answer. In the 60's crankshaft bearings were machined, but each engine's bearings were "touched up" by hand while the engines were being assembled. We have come a long way from hand tools these days. Casting technology being so amazingly accurate that the maching done to cylinder bores today is equivalent to what would have been considered a polishing 30-40 years ago.

With that long winded speech out the way I'd really like some input, if at all possible, why the use of conventional oils happens at all. Having recently purchased a Sears Garden Tractor with a Kohler engine (no flames about this, it's a better value than any JD in it's class) I was surprised to read in the manual that the use of synthetic oil is prohibited and will void the warranty. I called Kohler, they mean it too. This isn't just a break-in issue, it's at any point during the tractor's life span. I'm baffled by this, the customer service person I spoke with had no info and couldn't connect me to anyone who might explain why so I let it go. I know bringing up the tractor engine confuses the topic somewhat, but it's an example of the confusion that surrounds this topic.... being why would conventional oil have a place in any engine anymore?

Thanks guys / gals.

 

All I use is valvoline regular 20-50 oil on my motor. I have seen zero hp difference on the dyno going back and forth from regular to synthetic oil. I also blew my last engine with some very expensive royal purple in it. I will stick to regular old oil with frequent changes.
As for breakin I use straight 30 weight and run the motor at idle for 20 minute while monitoring the the oil pressure. Do a oil/filter change to get all the metal frags and dirt out. Next oil change at 500 miles after some varied rpm driving. Then I beat on it for a 1k miles before the next oil change. After that it is just every 2k miles.