Code PO12F

[poptop]

Let me run this by yall. 05 250. Oil cooler has 2500 miles on. It was put in by Ford Dealer in AL. When they did the Oil cooler they did not replace the EGR cooler. I was pulling a tractor it was only 5000 lbs. Nothing for the truck to pull. The truck said high temp on the dash display but the temp gauge was normal. Dropped off the trailer and the truck was fine. The servise engine light came on later. The code that popped up was PO12F. Coolant looked like muddy water. I know what the code means just looking for more imput .

[NYC F-350]

Since you already know that the P012F code is the coolant/oil temp correlation code, then you know what you have to do.
First is to do the two chemical flushes to thoroughly clean the cooling system, then replace the oil and EGR coolers (or delete it, your choice).
Finally, refill the cooling system with a CAT EC-1 rated ELC coolant. You will need 4 gallons of the concentrated form of coolant, no 50/50 mix since half of the cooling system capacity is retained by the block, even if you pull the block drains.