I might be over thinking this but I plan to flush my coolant system this weekend and will probably replace the thermostat then as well.

What do these trucks normally run for a water temp?
Is there a relationship between your water temp and your oil temp?
If so then would a bad thermostat cause your delta to be a few degrees higher?

Mine runs about 187ish all day long with a delta from 8 to 12.

Craig

 

Normal temperature is 190, and there is a relationship between coolant and oil where oil should be within 15 degrees of coolant (usually higher). 187 isn't bad, I wouldn't expect the oil temperature delta to change if you change your thermostat to 190. When you flush, reverse flush the oil cooler as well.

 

My 6.0 runs at about 190F unless working hard. Then it can rise to 210F causing the fan to run and it drops to the low 200s. This is in Vegas with 100F ambient air temps.
My delta is about 6F, again unless working hard. Then it can vary a lot but quickly settles out.
Not sure if I understand question 2, the relationship is the delta. If your oil cooler is plugged the delta is higher.
Yes, a bad thermostat will affect the delta.
Take a look in the Tech Folder for normal readings.
https://www.ford-trucks.com/forums/9...-pressure.html

 

If your coolant temp isn't close to 190*, then the delta may not be
accurate. Frequently, a weak t-stat causes the coolant to be low,
ie: 176, your oil temp will still likely be 190, or lower and this
isn't the situation to gauge your oil cooler.

My new t-stat keeps the ECT in the 188-190 range pretty reliably.