2003 Ford Taurus,car doesn’t totally warm up even when driving,1/4 on temp unit
Your thermostat may be stuck open. The way an engine warms is the thermostat. The thermostat stays closed to not allow the coolant to circulate allowing to stay in the engine block until it heats to the regulated temperature then opens to allow the coolant to circulate until it has to close again to heat the coolant again. It is a constant process of open and close to regulate the temp.
Your radiator fans also help regulate the engine temps. if your fans are stuck on all the time, that would also keep your engine temps down.
To Weekend Warrior’s good advice, I want to make sure that the OP knows about the toll that this situation takes on his motor oil. If the next oil change would normally be several months away, I urge the OP to have the oil changed MUCH sooner, because the oil undoubtedly contains a lot of condensation, which dilutes the oil and leads to a build-up of damaging oil sludge.
I expect WW’s idea is where to start. Thermostats live in hot coolant and over time will almost always fail eventually. Yours is 20 years old, with this symptom, probably time for a new one. They are considered wearing items so usually are pretty easy for a shop to replace, and the part is inexpensive. Ask for the old one back, and you’ll probably see it has warped a little, which prevents it from sealing 100% when the coolant is cold. This allows cold coolant to leak past the seal and into the radiator, instead of back to the engine, so the engine coolant never warms up like it should.
If it is a faulty thermostat, don’t cheap out on the coolant, replace it to rather than just topping off. As for the oil, I agree with replacement unless you just change it.