Again.. without knowing the brand it'* hard to say it it'* better then the other.

Synthetic isn't thinner then dino oil.. just more durable. ( as stated y 95naSTA )

Mobil 1 is a good safe bet. You can always look for German made quaker State.. both have done well in UOA ( Used oil Analysist )
If you're in Canada, it'* Esso XD-3 synthetic 0w-30 for me.
(i.e. 10W-30 )
the beginning is for cold start 10W
and the 30 is for operating temp 100C reading of the viscocity.

Tru as 90snSTA stated also that a lower viscocity 10w-20
at operating temp will yield a bit more power cause in a sense it'* thinner, but the chance of having your engine seize up due to lack of protection IMO isn't worth it. It might be ok for an emergency situation but not prolong duration IMO

You might also want to consider oil thats gasoline and diesel safe.
Diesel engine oil generally has higher detergent level then standard oil

Your missing oil could just be as simple as oil consumption that is burnt off in the combustion chamber so you don't see it ..
Opensourceguy has mentioned a trick that I will pass on.. There'* special UV pallette yo can get and in this case put into your engine oil.. run it for a while, if there'* external leak.. when you shine the UV light on it, it will glow right up and show you where it'* coming out of

Be

If you don't want to list the brand here.. check out www.bobistheoilguy.com[/b]

Can you go from regular oil to synthetic in one oil change or is a process?

you shoulld be able go right to synthetic. The only thing I would recommend is changing the first batch of synthetic at the listed oil change interval as it may remove some sludge that was left behind from the dino.. past that point, you can then go for extended oil change interval.

EDIT: your choice of oil filter is just as important also. Delco'* Purolator'* or Wix are good.. stay away from FRAM or the likes.. the filter is just as important as the oil you put in.. they're both the blood of the engine

If you have an oil leak why run $4-5/qt oil? that'll get pricey quickly. The big reason not to switch is the detergents in syn, which clean out gunk that'* been plugging your leaks all these years. Once it washes the system clean, you may have more leaks. I switched @ 112k, and the only leak I may have is my oil pan gasket.

Otherwise I prefer Mobil1, it'* available everywhere, it'* widely used, and i have a lot of options. a 5qt jug from walmart is perfect.

You can go back and forth whenever you want to either type.

I use mobil one now...heck its cheap...only 20 bucks....and I dont feel too bad if I dont strictly adhere to the 3/3000 rule....my engine is super quiet now that I switched to full synthetic...winter starting is a lot easier....I should make it to 200,000 no prob....

I agree. Use cheap stuff untill you can get that leak fixed. Otherwise it'* money down the drain.

I've been useing valvoline max life in my 92 olds and at the moment i'm at 285,244 on the original engine and tranny and i've had no problems with it and it runs just great.

You are also beat'n the crap out of that transmission. When was the last time anyone changed that transmission oil and filter? And if/when you do, use Dexron III oil. Do NOT use a synthetic transmission oil(IMO).

yes that is NOT good for your trans, shifting it manually will lead to an early death, i will promise you that

In my own vehicles and those that I maintain, I use Valvoline DuraBlend during the low mileage years. As they approach 100k miles, I switch to the MaxLife. Oil changes are regularly done around 3,000 miles, and the cars are not abused. That doesn't mean they are babied...just not abused, which will likely have more to do with engine life than which decent quality oil is used. Most of the cars have well over 100,000 miles, and a couple over 200,000.