i go a catipillar dealer and buy a oil test kit for $14, take a sample and drop it off at the dealer. In a couple weeks i get an anylisis statement back with the results. i have sent in used amsoil samples with 15,000 + miles on it and the statement can back good and to keep up what i am doing.

 

This may be a little outdated now...a conservative figure for fuel mileage if changing engine and drivetrain is 2-3%, some may be better. The only drawbacks I could think of would be age and condition of engine. If it's using oil now, it probably won't get any better. If there is significant sludge and varnish buildup in the engine(hard to know) and it happens to be working as a gasket plug in places, a synthetic and clean things up and reveal a new leak.
Only other thing is cost and that all depends on how you plan to use it. Extending the intervals saves money in the long run.

 

I am buying an F350 now 03. I noticed an oil leak the dealship said it was the oil sending unit and the oil looked black to me. burnt oil is scary so their answer was it was Mobil 1 synth and that's why it looked different than dyno oil.. is that BS?

 

have never though that snythetic looked different from conventional oil

 

a hockey friend of mine owns Gibson Transport in Alliston and they use Rotella oil in all of there rigs.

You have probably seen them on the hi-way

They do i lot of california to Toronto , ontario round trips

So i figure if they use it with good success i use it in all my service vehicles
and welding machines, power washers, gas trucks and vans..

 

There is no advantage to using dino oil except initial cost at the checkout counter. If you work out the math, its actually cheaper to use synthetic in the long run!

To their pockets. Amsoil is a middleman, they just use Mobil's oil with a modified additive package. Their business it skimming a percentage from dealer's income, not oil production or R&D.