As far as heat is concerned down south a 40weight either from a 5 or 15 is still a 40weight oil, plus if he is going to be towing a 34' trailer syn is definately better at protecting the engine because syn can protect far better from break down due to heat.
I would be more concerned about the tranny fluid towing something that big. If not already running syn in the tranny seriously consided switching
Cheers
I would be more concerned about the tranny fluid towing something that big. If not already running syn in the tranny seriously consided switching
Cheers