Originally Posted by calxfire
So is it ok to use 5w-40 if there are no 0w-40 available? My limited understanding of oil viscosity is that it has more to do with expected temperature variation rather than the actual "quality" of the oil. Maybe in the colder regions specially in the winter 0w-40 would offer better protection at starup because it would flow more freely but once the engine has warmed up then it would not matter. So my line of thinking is that in the temperate regions like California or Florida 5w-40 should be ok. Would I be doing harm to my engine if I did this?
The issue is not completely the temps outside during the day etc. That is where the second number comes from so both are rated at 40. When warm, the oil will compare to 40 weight oil. The issue is during start up. When your engine is not warm, the oil needs to flow as quickly as possible. This motor like another already stated has very close tolerances thus needs a very thin (when cold) oil to flow very quickly to all vital parts so it does not cause any more premature wear over time. It helps that if you live in an area that stays warm over night all year round but...... My preference is Amsoil over Mobil 1 but due to them not making a 0W-40, I did not switch. I am not claiming that 5W-40 will harm the motor in warm climates but there is a reason for it calling for 0W-40 so even here in Texas, I stuck with Mobil 1.
I do know someone else that used 5W-40 and once in a while they get tapping noise for a few seconds at times during start up which did not ocur with 0W-40. Could just be a coincidence but maybe not.
Steve