P0128, 2004 3.0

[flyin-lowe]

My son's truck, 120K miles. Light came on tonight and reads P0128. From what I am reading most likely cause is thermostat. I plan to replace that in the morning. Watching YT videos seems really straight forward. Couple questions though, I looked on Oreilly's website tonight to make sure they had them in stock, they show several different temperature's. Which one do I need? In Indiana if that makes a difference. What would the stock thermostat be as far as the temp goes? Also, I assume on this year Ranger the standard coolant is fine if I need to top it off? Lastly, will I loose much (if any) coolant if it's been parked for a while? Didn't know if I need to drain any or since that hose is high, should it not be holding anything if it has not been running?

 

[flyin-lowe]

I went out this morning to check the coolant levels and I noticed as I looked around there was some moisture around the thermostat housing. I went ahead and bought a new housing (aluminum) and thermostat. I am 90% certain the thermostat I took out was in upside down but wasn't really paying attention because as I pulled the housing off I was trying to get my drip pan kicked into the right position, but the way I pulled it out and had it in my hand i "think" it was upside down. Am I dreaming, or is it possible it could have been upside down since I have owned it that past year? Got the new housing, stat, and gasket installed and a 50 mile test drive with no CEL so all appears to be well. The temp gauge went to right at straight up and down in the dash and stayed there.