"Would you recommend a 5W-40, 10W-40 or 15W-40 lubricant for a Hot weather country? Would 5W-40 be less viscous compared to 15W-40 engine oil for cold starts in the morning? What would be the effects on the engine's performance and protection? This will be put to use on fleet in a Hot weather country with an average of 32-37 degrees C at midday and high humidity (60 percent). Early morning and late night temperatures will be around 24-27 degrees C. Since there is no winter, should I just ignore the 'W' value and focus on the 40?"