Yeah fill filter with injector cleaner so its nice and strong for a bit, then put the rest of it in your tank. I put mine in 1/4 tank rather than full so it was stronger.
The thermostat is the valve that opens the coolant up to the radiator, if this is stuck open or failed your coolant is open to the radiator all the time resulting in longer warm up, one test is to coast down a long downhill when its cold outside and see if your temp gauge drops.
Also did you use a genuine temp sender? The sensor has 2 sensors in it, one for ecu and one for dash
The thermostat is the valve that opens the coolant up to the radiator, if this is stuck open or failed your coolant is open to the radiator all the time resulting in longer warm up, one test is to coast down a long downhill when its cold outside and see if your temp gauge drops.
Also did you use a genuine temp sender? The sensor has 2 sensors in it, one for ecu and one for dash