I was driving home last night when my Service Engine Soon light came on. This morning, I took it to my mechanic and he pulled up code P0125B and said I need to replace the thermostat. I'm curious if the truck will stall on me if I continue to drive it for about another week til payday, when I'll replace the thermostat? Thanks.

2000 Ford Expedition XLT - AWD - 5.4 Triton V8 - 112,000 miles

 

Keep in mind this may not be the problem for sure. A code P0125 may mean that one or more of the following has happened:

Insufficient warm up time
Low engine coolant level
Leaking or stuck open thermostat
Faulty coolant temperature sensor

If you do go for the thermostat fix, it's a very simple job, if you'd like to try it yourself and save some money, here's some instructions to help you.

1) Put a small drain pan directly underneath the radiator drain valve.

2) Open the radiator drain valve, using a pair of slip joint pliers if necessary and remove at least two quarts of coolant.

3) Close the radiator drain valve.

4) Take the upper radiator hose off the thermostat housing on the side of the engine. Depending on the type of clamp used on your particular vehicle, you may use rib joint pliers or ratchet and socket to remove the clamp.

5) Disconnect the upper mounting bracket holding the power steering reservoir in place. On some Expedition models, this is necessary to gain access to the thermostat housing.

6) Remove any other hoses attached to the thermostat housing if you have a 5.4L engine model. Use pliers or a ratchet and socket to disconnect the hoses.

7) Unscrew the two mounting bolts from the thermostat housing using a ratchet, ratchet extension and socket.

8) Lift the thermostat housing and thermostat unit. Discard the thermostat O-ring.

Install the Thermostat

1) Install the new thermostat in place, along with a new O-ring. Make sure the thermostat spring points towards the engine.

2) Set the thermostat housing in place and start the two mounting bolts by hands. This will prevent damage to the threads.

3) Tighten the two thermostat housing mounting bolts using the ratchet and socket.

4) Connect the upper mounting bracket that holds the power steering reservoir in place if you had to disconnect it.

5) Hook the upper radiator hose to the thermostat housing and tighten the clamp using the rib joint pliers or ratchet and socket.

6) Connect any other hoses you disconnected from the thermostat housing if you have a 5.4L engine model.

Refill the Cooling System

1) Add 50 percent water and 50 percent anti-freeze to the cooling system. Pour the coolant through the radiator neck using a funnel, if necessary, and make sure the coolant reservoir level is between the "low" and "full" marks.

2) Turn on the engine and let it idle for about four minutes to bring the engine to operating temperature.

3) Check the coolant reservoir and add more coolant to bring the level between the "low" and "full" marks if necessary.

4) Turn off the engine.