1992 454 7.4 liter oil

Some people think thicker oil is better. A thicker oil may be the right choice if outside temps are high enough but not as a general rule of thumb. Some will look at the oil pressure gauge, see the higher readings with thicker oil and think that's a good thing. The pressure readings are higher because the oil doesn't flow as easily. Less flow equals less lubrication and less cooling to critical components. You want the oil circulating through the engine, providing clean, cooler oil. Not thick oil that doesn't want to move.

Check the engine manual and see what oils are approved based on temps. I would always choose a multi-weight over a straight weight oil. Outside temps are never a constant.