Reply To: Temperature on long trips – GT125R
50 will will have a slightly higher heat tolerance before the oil starts to break down. The “10w” in the bottle must stay that way forever as the hardest life the engine gets is also when you start it , the oil must race to the crank and lubricate so the parts don’t degrade too fast (metal to metal grinding)
15w/20w is too thick for our climate. However, 40/50 on the bottle (without “W”) is safe for all year use.