I wouldn't run any lower than a 30 weight oil in a magnum engine, that is the lowest viscosity they where designed for. Lower viscosity oil doesn't lube the bearings as well, newer design engines have tighter tolerances so you can use lower viscosity oil in them.

 

The main bearings are lubricated by a hydrodynamic liquid wedge that forms when the crankshaft is rotating. Oil in incompressible so as long as you have oil there, low viscosity won't matter, it's lack of oil or extremely dirty oil that would cause bearing wear. The upper reaches, such as the push rods are lubricated by a thin oil film so that's were you need good oil flow and a high strength oil film. Full syn all the way...flows better, protects better and keeps the engine cleaner. Note that he said pressure is higher when he starts the engine, or before warm up. High viscosity, cold weather, cold engine.... you get the idea.

 

Higher viscosity oil protects better than lower viscosity oil, I would never recommend using a lower viscosity oil than what an engine was designed for, especially not 20 weight in an engine that was designed to use as high as a 50 weight oil. It is likely to make the engine more noisy as well, as for keeping it clean diesel oils have way more detergents in them than gas engine oils and do a great job of cleaning up the engine and keeping it clean.

 

Viscosity is ability to flow at a certain temp, not how well an oil protects. That's film strength. Anyway, don't want to start an oil war. Everyone can keep using what makes them happy. If his oil pressure is truly high, thats the way I'd go along with a larger oil filter. First I'd confirm it though with a mechanical gauge or changing out the pressure sender.

 

 

Its good to know its not a uncommon thing in these motors !
At idle after driving i noticed it was a lot lower but ill look again soon after changing oil at start up to compare .

I also didnt think it was a good idea to ever switch around from conventional to synthetic oils then back an forth.but i may be wrong if your in a area with -32 at times ..,luckily im in Tn so its not that extreme.
Ill stay with the 10w 30 conventional an go with high milage oil for now .Maybe check with a guage later.
Thanks

 

Its good to know its not a uncommon thing in these motors !
At idle after driving i noticed it was a lot lower but ill look again soon after changing oil at start up to compare .

I also didnt think it was a good idea to ever switch around from conventional to synthetic oils then back an forth.but i may be wrong if your in a area with -32 at times ..,luckily im in Tn so its not that extreme.
Ill think stay with the 10w 30 conventional an go with high milage oil for now .Maybe check with a guage later.
Dodgevity may be correct on thickness factoring higher pressure too..i added some sea foam [4oz ]to oil at idle for a while before i was going to change it an it seemed to be at a much lower reading on guage.
Does that indicate that a 5w30 would bring it down being thinner ?
Thanks

 

The "W" stands for winter, so that's the cold viscosity. This means it flows better than 10W when cold, so yes that should bring down the pressure. When the engine reaches normal operating temps, 5W30 becomes a 30 weight oil.... just like 10W30.