Oil Viscosity - 1990 Ford Mustang?

Just recently bought a Mustang, but without the owner's manual unfortunately. What's the best oil viscosity for it? It's 2.3L ( don't know if that helps at all) and I think 5W20 was mentioned as the best, just not sure. Thanks.Oil Viscosity - 1990 Ford Mustang?
That engine calls for 5W-30 year round, 10W-30 okay to use as well. 5W-20 is too thin to use for all but the coldest conditions.Oil Viscosity - 1990 Ford Mustang?
5w30 is a good all year oil but some people use 10w30 if the engine has some miles on it,the thicker or higher viscosity slows down oil leaks and oil consumption while boosting oil pressure,as far as brand use the brand you trust Castrol is good but Pennzoil,Quaker State,Shell,Citgo,or Cenex are equally good,the biggest difference in them is the dye added for product identification and promotion of product to convince people to buy a particular brand.
The best oil to use for this engine year round is Castrol 5w30. I have rebuilt many of these engines and recommended the owners start using it on a regular basis. Out of the 100's I have rebuilt only 3 have died (due to an irresponsible owner not changing the oil regularly) and the others have more than 250k miles on them.
Personally I would use 10w30 in the summer and 5w20 in the winter if you live in a cold climate.

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