I was wondering what would the benefits and drawback would be of running straight 20weight in my 1987 GL-10 Turbo?

Have you thought of any benefits yet?

why use a single viscosity? - I don't know andvantages

 

you dont have as many engine-protecting additives as multiviscosity, you are using dino oil, which breaks down faster than synthetic, and you have to change the oil seasonally - I think there was even a recommendation in the owner's manual not to use single viscosity

 

I have a neighbor/good friend who spec'd oil for industries (including auto aplications) at Mobil for years who told be that you should always avoid single viscosity oils if possible because they are poorer in quality/operating characteristics

 

I still can't figure out the benifits - even if the oil is cheaper, it will wear your engine out faster. Better oil is cheaper than an engine rebuild.

well i live in a warmer climate over all and i run 20w50 in any vehicle i have with over 150k on it(hey that all 3 lol)except for my benz since its a diesel

Subys are pretty forgiving as far as oil goes, but the one problem you will find running high viscosity oil in cold weather is that the suction created by the oil pump during warm-up tends to suck in one 'O'-ring on the mickey mouse gasket between the pump body and the block.

This allows aeration of the oil and subsequently you get the horrible valve tick that we all know and love.