I got this off the Amsoil web site.

The only time we recommend a 40 weight oil, such as AMSOIL's 10W-40, to a customer in a passenger car or light truck application is if the vehicle's engine is excessively worn and consumes oil at a higher than normal rate or if the vehicle is being used for very severe duty, high load, high temperature applications.

Higher weight oil has bigger molecules and will take up the extra clearance of an older high mileage engine. This will raise the oil pressure. That is if the pump is not worn out.

Ralph

1991 Toyota 4x4 Standard Cab Pickup.
engnbldr cam and head.
Doug Thorley Headers
Home Made Cat Backs
30x9.5x15 BF Goodrich All-Terrain M/T KM2