I've got a two cases of 10W30 synthetic oil that I bought for a car I no longer have and would like to use it in my 96 3L ranger with 54,000 miles on it.  I live in the sunny south so I don't need to worry about the improved cold weather viscosity performance that 5W30 gives.  They both have similar performance on the hot end although some websites say 5W30 is a little better for a hot climate.  
The high temperature end doesn't make a lot of sense to me. If the ambient temp is 95 F and the engine oil temp is 206F +/- why would Summertime temps have anything to do with it?
Has anyone else substituted 10W30 for 5W30- if so how did it work out?
The owners manual specifies ONLY 5W30.
				
			The high temperature end doesn't make a lot of sense to me. If the ambient temp is 95 F and the engine oil temp is 206F +/- why would Summertime temps have anything to do with it?
Has anyone else substituted 10W30 for 5W30- if so how did it work out?
The owners manual specifies ONLY 5W30.
 
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