I just changed the oil cooler lines on my 81 SD ,the bottom fitting on the cooler has very little threads left on one side of it .It snugged up but I found a used one so plan to install that.My question is I was reading a thread here that said the oil doesn't circulate until it reaches either 95c or 115 c depending on the thermostat used in the oil filter housing so if you have a cool running car and live in a cool climate as I do dose that mean the oil in the cooler sits there for years?seems like it might break down sitting?
William Rogers......

We used to do oil tests at work and the life of lubricating oil when it is cool is almost infinite. Its when it gets hot that it polymerizes and changes it characteristics.

I'm sure that if you drive up a hill even in cold weather, the oil will get warm enough to circulate thru the cooler.

It is nothing to worry about.

P E H