Is straight PUP 0-40 ok to run in the 5.7 Hemi? Should I mix 5-30? What's the benefit of mixing the two instead of straight 0-40? I'm also using the SRT oil filter for my next oil change. Any advice is apreciated.
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Oil Viscosity (Oil Thickness) is an important decision when choosing your oil, regardless of oil brand. Because all engines are constructed with “very specific” clearances between internal engine components. Those clearances are determined by the engine designers (engineers) and that’s why they give you the recommended oil weight. So why is this important? It’s because internal engine components are cooled by oil “Directly” and cooled by the coolant “Indirectly”. So running a thicker oil than what is recommended is a bad idea in most cases. Because oil “flow” through internal engine clearances is critical for proper lubrication and to pull heat from internal engine components. The engine oil temperature in these areas of the engine can be 50-90 degrees “Hotter” than oil sump temperatures; thinner oils flow better than thicker oils pulling more heat from internal engine components. I tested this by switching from manufacturer (Dodge Ram) recommended 5w20 to 5w30 while canyon racing in the North Georgia mountains, and my oil sump temperatures were 16 degrees “Hotter” on average running the thicker oil. Why? Because thicker oil’s flow “slower” through internal engine components and get hotter, driving up bearing temperatures, reach or exceed the oils thermal stability, lubricate less affectively and pull less heat from your engine. Thicker oils do provide options with mechanical noise, but mechanical noise doesn’t necessarily mean there is a problem with the engine; usually just annoys the vehicle owner. In addition, I wrote certified letters to the Dodge Ram manufacturing plant in Mexico, corporate office in Ann Arbor Michigan and corporate office in London United Kingdom and asked them what oil viscosity was recommended specific to the cam and bearing clearances on the 4th gen Hemi. And to my surprise I got a response; they gave me the cam and bearing clearances and only recommend 5w20; no surprise. Engineers know what they’re doing, and they know what oil viscosity is ideal. Bottom line, stick with the recommended oil weight from the manufacturer, unless you live/work in extreme cold climates were thinner oils (0Wxx) will serve you better. Oil temperatures while daily driving to work with the 5w30 was only a minimal 2-3 degrees hotter than the 5w20. With that said, I think you will be ok with a 30w oil “IF” your truck is a daily driver; if your racing I would recommend the manufactures recommendation 5w20. The 40w oil is too think considering the Cam and bearing clearances.
