Hello Everyone,
I was contemplating replacing the thermostat myself on my 2010 Ford F150 5.4 V8. Seems fairly straightforward. The tutorials that I found start with draining the coolant/fluid. Can I remove the thermostat housing and replace the thermostat without draining the coolant? Is there alot of coolant in the top hose that will leak out when I remove the thermostat housing? I didn't know if the tutorials mentioned this because they assumed a coolant change was also going to occur or to prevent major coolant leakage from the top hose when the housing is removed. Thanks in advance.

 

The radiator is slightly higher then the thermostat housing, so yes, you will lose coolant from the block side when you remove the thermostat housing.

I'd drain down the radiator, change the thermostat, then refill with clean, fresh 50/50 mix coolant.