My parents had a Briggs PPDX20, 20kw generator installed at their house last year, V-twin 993cc Briggs Vanguard engine. According to the manual it has SJ rated synthetic 5W30 from the factory. My mom wants me to do the maintenance on it, Briggs recommends 15W50 in this engine for continous use commercial duty applications, 20 degrees to 130 degrees. I think the 15W50 would suit it much better, and being natural gas it burns very clean. I see Redline offers a Powersports 15W50, Amsoil offers a 15W50, and was also looking at HPL, not sure if they have a 15W50. It has a 10 year warranty, also considering just sticking to the Vanguard 15W50. I dont mind spending the $$$ for oil for this unit, the oil and filter will be changed every 100 hours or yearly. Which oil would you run? South Louisiana so it doesnt get very cold.