I have a 05 F250 6.0 with 108,000 miles on it and this is my first diesel truck to own. Three months ago I put a coolant filter on because I noticed the wrong coolant was in it after researching what kind the truck is suppose to have (Purchased truck in Nov. 2011 with 101,000). So I flushed the engine according to a post I got from this site, installed Shell ELC, and installed a Bully Dog Coolant filter system on the truck. A month ago, I noticed the truck was leaking coolant from the top radiator hose, felt hose which was rock hard, so I changed the filter, changed the thermostat, and installed an O'Reilly coolant resevoir cap (they did not have a Motorcraft in town at all). I have not drove the truck till today and I noticed it was leaking again from the top hose and the top hose was hard again, so I cracked the cap on the coolant resevoir which removed the pressure of the top hose.
My question is I know the truck needs about 11 pounds of pressure for the coolant, but why is it that the top radiator hose is feeling rock hard like there is too much pressure? Do I need to install a temp gauge in the coolant to make sure my new thermostat is operating correctly or do I have another issue at hand?