I realize that recommended oil viscosity depends on climate (average ambient temperature). My late model Mustang 4.6 SOHC specifies use of 5W-20. This is the lightest oil I have ever seen specified for any vehicle. I guess this will be fine for winters in the northeast (average maybe 25 - 45 degrees F), but how about summer? I read somewhere (can't remember where) that 5W-20 may not be good for high speed driving in summer weather. I think I'd want to use at least 5W-30. I wonder if there's anything wrong with using 10W-40 in these engines? However, I am not a believer in using oil that is "thicker" than necessary. Also, regardless of the weather, is
5W-20 adequate for severe full-throttle operation such as drag racing in these engines? I would think that if Ford specifies the use of 5W-20 that it should be safe for almost all types of driving in almost any climate.... or was Ford forced to specify this lighter oil to meet certain fuel economy regulations, and perhaps 5W-20 is truly not the "best" thing in terms of the longevity of the engine internals?- posted
20 years ago