I'd go with synthetic (Moble1), 10W40. I would doubt that the operating
engine oil temperature is much higher when the temp. outside is 120 degrees
vs. 60 degrees. The thermostat should keep the operating temperature about
the same (I would imagine the temp. of the oil might be like 20 degrees
hotter, but I doubt that has any significance when it comes to the
lubricating properties). And even if it is significantly higher, the
synthetic will break down less than conventional oil.
I'll try it. Synthetics will go more miles? I have heard that you can
change after 5,000 instead of 3,000. My engine seems to be running cool at
the lower end of the operation temp.
Thanks for the input
Mobil 1 recommends that you change the oil at the upper end of the range
that the engine manufacturer recommends (so in this case, probably 5,000).
Other synthetic oil makers say that you can go longer, like 10,000 or 20,000
between changes. Personally, I am not sure whom to believe.
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