I put Royal Purple 10w-40 in my '70 Olds 442, which is mostly stock. The cold oil pressure was normal, but once the car warmed up, the oil pressure was lower than with the oil I normally use.
I drained out the RP, and put the normal dino oil I typically use back in. The warm oil pressure returned to normal.
My opinion is RP loses viscosity as it gets warm.
I drained out the RP, and put the normal dino oil I typically use back in. The warm oil pressure returned to normal.
My opinion is RP loses viscosity as it gets warm.