So I had my uncle asked a few engineers at ford about this because my parents car 02 mountaineer has a 4.6L and ive been using 5w20 mobil 1. I think there answers are complete garbage. Here's what they said.
I am going to assume the customer has a 4.6L engine since he states using 5W-20 oil. It is best for the customer that he stays with 5W-20 oil to make sure he gets the best protection (and fuel economy) for his engine. 5W-30 should only be used with 4.0L engines in the Mountaineer. Below is what we state in owner guide:
"Use Motorcraft SAE 5W-20 or an equivalent 5W-20 oil meeting Ford specification WSS-M2C930-A. SAE 5W-20 oil provides optimum fuel economy & durability performance meeting all requirements for your vehicle's engine".
Per your inquiry here is the answer. In layman's terms your brother should stick with the 5W-20 weight oil since that's what specified and what the engine was tested with. The 5W-30 is going to have a higher viscosity when the engine is cold and therefore may not provide ample lubrication during critical start time.
I am going to assume the customer has a 4.6L engine since he states using 5W-20 oil. It is best for the customer that he stays with 5W-20 oil to make sure he gets the best protection (and fuel economy) for his engine. 5W-30 should only be used with 4.0L engines in the Mountaineer. Below is what we state in owner guide:
"Use Motorcraft SAE 5W-20 or an equivalent 5W-20 oil meeting Ford specification WSS-M2C930-A. SAE 5W-20 oil provides optimum fuel economy & durability performance meeting all requirements for your vehicle's engine".
Per your inquiry here is the answer. In layman's terms your brother should stick with the 5W-20 weight oil since that's what specified and what the engine was tested with. The 5W-30 is going to have a higher viscosity when the engine is cold and therefore may not provide ample lubrication during critical start time.