Currently I have Valvoline All Climate 5w30 in it. I might give 5w40 a shot. However I do have a question. If I use 5w40 in Summer, would there be a problem in using 5w30 during the cooler months?
Is there an issue using a thicker oil and then going to a thinner oil afterwards?
It depends how sensitive your Hemi is to oil flow rate. Generically, there is no issue changing oil viscosities as long as they are proper for your application conditions (ambient temp, truck duty cycle loading).
Some members report low oil flow issues below 50F with cold starts (lifter ticking). Some have gone to higher flow oil pumps. Some have increased idle speed back to what once was normal (750 rpm). Some shut off engine at high rpm (1,000 rpm) to pump up lifters prior to shutdown. It has also been shown that oversize synthetic oil filters help, even though technically they should make no difference to a "constant volume" gerotor oil pump. Some pre-lube the oil galleys by cranking engine without starting for several cycles (I do this). Some go all the way and add an auxiliary pre-lube external oil pump and turn on without cranking the engine. Some add oil pan heater to keep using "summer" (higher) viscosity oil during the winter (this doesn't address leaving the vehicle where there are no plug-ins....engines will be near ambient within an hour after shutdown).
So, here's the thing - low viscosity oil is ONLY important during cold ambient startup, and is most affected by colder ambient air and using high ester synthetic base oil (Red Line).
There is no single answer for all users in any area of the globe. Red Line still seems to be the gold standard for Hemi valvetrain lubrication, bar none. 5W-30 comes closest to most applications. Where it is cold, we start discussing 0W and / or combinations of oil flow improvements such as mentioned above.
Where it is very hot ambient, and / or heavy tow loading, SAE 40 summer weight comes into play due to higher bearing and cylinder loads. Heavy Duty trucks have oil cooler radiators to keep oil temp from getting to high, I saw recently that half ton trucks did not. So adding an oil cooler to a half ton in high ambient would be immensely helpful.
