Thanks for the quick reply... I should clarify...

The cap issue was a month back. I fixed it by putting the cap on tightly as it should be, as soon as I noticed. I have driven for about a month (1600+ mi) since, with no problems, fine engine temp that stays consistent, and the water level is always at the right height. The cap was new last summer, so Im pretty sure its OK... Im more concerned with the thermostat.

Ill check the cap, but since in warmer temperatures it was always fine, and consistent, regardless of the cabin temperature setting change, I have to wonder beyond a cap/pressure issue.

Good point about the oil cooler thermostat. My one worry is then that: can we safely assume that even in high speed driving in temperatures in the teens and below, the oil is getting up to a proper temperature to safely protect the engine?
I worry, because a lot of the antiwear additives and oil properties depend upon a proper operating temperature, and I would assume that the oil temp thermostat is set to the middle or upper area of the 'OK oil temp range)/

Thanks for your help,

JMH

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Current Diesels:
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