4.6 P0128 and thermostat

[ROBinGa]

Wife drove the Explorer today and says SES light came on. Engine runs smooth and no apparent problems. I took to Advance and their OBD tool says P0128. Guy says no doubt change the thermostat. I came home and looked on here and YouTube for help but don't see real specific how to help that addresses fluid for the change out. I gather that I need to unhook the upper radiator hose, take the two bolts off that hold the upper house inlet piece and thermostat is underneath it. Looks simple enough to take that and o ring seal out and install new parts in reverse. But how much if any coolant do I need to drain? And then once the thermostat and seal is replaced how would I add the coolant back - just run engine and keep adding to the overflow tank as needed? I've never done anything on a radiator or cooling system so just don't have this experience. For more background, today was first day this year that temp has gotten into the 40s overnight so I bet first time she has used any type heat. The fluid in the overflow tank is actually at top of the cold fill range lines. I put a few ounces in about a week ago in there just to make sure it was on upper range of fill lines. It was on lower line before that. Wondering if me adding the 50/50 blend fluid had anything to do with this happening all of a sudden. Temperate gauge needle reads right in middle on dashboard and the heater works fine with plenty of heat. I squeeze the upper radiator hose and can see the fluid in the overflow tank pulse as I do that. Thanks

 

[rwt101]

That code ,from what I read, states that the engine did not come up to temperature fast enough. Before replacing things I would clear the code and see if it comes up again. If the temp gauge is where it normally is and the heat is good , there might not be anything wrong.

If it does it again then you can think about changing the thermostat.
Bob T

 

[ROBinGa]

Good to know. So my Advance location will not clear codes any longer nor will they let you "borrow" their scan tool, they come out and plug in and read for you. Do you think this code will clear itself over time if all is well and no need for new thermostat?

 

[rwt101]

It should clear itself if the condition does not return. IT will take a while, I forget how many restarts it takes. But keep an eye on the temp and also on the coolant level. Don't let it overheat.
Bob T

 

[Joe in NY]

If the thermostat is weak then the engine will always have a slow warm up, especially as winter comes. With that being so the code will never clear..

 

[rwt101]

Well then he will have to change it.
Bob T

 

[ROBinGa]

Update to this post. I did monitor like rwt suggested and the temp gauge has been right in normal zone and all operation of heater and engine seem normal. The SES light has now gone off on its own yesterday without clearing it with a code reader. If the light does come back on I will dive into the thermostat change but right now all seems back to normal. Thanks RWT101