Here is the real story again;
Use Dino oil first few thousand miles of new or rebuilt engine because it allows metal to metal parts to wear or 'break in'. This is needed to 'seat' rings and such or you will loose compression and burn oil.
Switch to Synth oil at any time. Synth oil stops metal to metal wear almost completely unless you waited too long or have a defect in the oiling system. Some parts of some engines get poor oil lube so they wear anyway, like some engine's valve guides.
Dino oil breaks down quickly and allows if not causes your engine to foul itself up with burned and broken down oil deposits. These block oil passages and deposit non lube particles on bearings, etc.
We use Dino oil because that was all that was available back when cars started needing oil that was plentiful and cheap. Bear grease was used on wagon wheels but too expensive to refine for cars. Dino oil was not chosen because it was good for cars, but because it was the only thing that fit the need.
3000 mile oil changes are a fantasy that keeps the oil companies happy and discourages any great strides in improvements in the standard oils and oil additives used in modern dino oils. They love to sell 4 or 5 quarts of oil for every 3000 miles driven by every car, wouldn't you? But government forced car manu to at least change it to 5000.Synth oils are usually good for 25000 miles but vary according to your specific driving situation (we always have to say that). You will notice that some Synth ads on TV are now advertising 15000 between changes. They could say
25000 but then no one would believe them. I personally, as a past warranty and tech rep from a major car manufacturer, would recommend Synth oils with changes at 15000 miles EXCEPT!;You must follow your warranty schedule while in warranty, You must follow your extended warranty schedule while in extended warranty if you bought one. Use Dino oils for first 5 to 10,000 miles on new or rebuilt engines, Use Synth oils while in warranty after that if you are going to keep car over 140,000 miles or so. If you trade in your cars every 2 or 3 years with around 100,000 to 130,000 miles, you probably can use Dino oils and let it be the next guys problem.
Synth oils can usually be run at a weight lower than usual and improve gas mileage. So if you use 10W30, you can usually use 5W30 Synth with same protection and better mileage.
Synth will find any potential leaks faster than Dino oils. So if you have a potential or slow leak, Synth will hasten it in most cases.
Your engine will not get eaten alive while Synth is in it, but it will while Dino oils are in it. Remember that when thinking that Synth is a 'Cleaning Agent' as that is a deception. Otherwise you can switch back and forth at any time.
Also, refer to the above when thinking about purchasing the marketing idea of 'Blended' oils. 1 Qt of crap mixed with 4 Qts of Synth yields 5 Qts of crap. However, no bottle of Blended I have ever found even says how much Synth is in it, could be 1 one hundredth and it would still be a 'blend'.
RedCrow