Originally Posted By: dnewton3
Doesn't really matter how hot it gets outside (ambient). What matters is how well your cooling system operates.
Ambient temps don't effect to total load near as much as they effect the rate of energy transer. As long as your cooling system is sized properly, you should be able to overcome any heat load generated. Think about it this way:
1) it's ugly cold outside (-20); it takes longer to warm up, but it does eventually get warmed up to operating temps.
2) it's ugly hot outside (+110); it warms up darn quick, but it doesn't get any hotter (final temp) than if it were +75 outside.
Assuming it's running fine, then it's probably thermostatically controlled somewhere between 190-210 deg F all the time. So to that point, the xW-20 grade oil will work the same, regardless of what the outside temp is. In fact, even dino would be fine at those temps.
Now if you have a cooling system issue, such as restricted fluid flow, clogged heat exchanger (radiator), etc., then the coolant will get too hot and that will make the oil hot. But that's not the oil's fault now, is it?
I agree somewhat but with an oil temp guage in the GN and a very good cooling system, my oil temp rises in the summer by nearly half of the ambient change. Water temp runs dead on 170 degrees summer or winter.
Since I see hot summers, long trips, and my engine originally called for a 10-30, I use a 10-30. If I ever decided to track it, it would get a 15-40.