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