I'm sitting here 100 miles from Death valley, and I'm sure even round here you will want a thermostat in the oil cooler path, the high today is 56 degrees F (13 C). Great driving weather, but no risk of overheating!
I have Morgan Custom's oil cooler for summer driving, this includes a mechanical thermostat so that it only kicks in when needed.
I once drove through Death Valley in the +8 with the roof down it was 48C (118F), interestingly the radiator fan didn't come on unless I slowed down or stopped with the temperature gauge showing no more than 120. The driver however was casseroled for a couple of days.
