Navigator 2000 got Service Engine Soon with code P0125. That means Engine coolant Temperature always low. The navigator dashboard shows temperature on dashbord around 25% above cold when driving for about 10 minutes. The temperature rises from C towards H but stays around 20% to 25% but never goes up. Navigator runs fine. It could be thermostat bad or Engine Coolant Temperature Sensor.

Do you know where is temperature sensor located? How to test it? Any experience with this code?

Thanks
John

 

It would seem that you may have an air pocket in the engine. The gage will not register if the coolant is not touching the sensor. There is also the possibility that the wrong thermostat is in the engine, possibly a 165* would cause the gage to register a low temp.

 

Moto Mel,

Thanks. Do you know how to test Engine Coolant Temperature Sensor. Where is this sensor located?

Thanks John

 

Your t-stat is the problem. You can rule out the temperature sensors as the problem because both are reading low. There is one for the gauge and the gauge is on the low side, then there is a second one that reports temperature to the ECM. The ECM also thinks the engine is to cool because it is giving you a low temperature code. It's unlikely that both sensors would go bad at the same time, so the common part between the two is the t-stat.

 

Replace the thermostat with a new Motorcraft unit, refill the system with a 50/50 mix, and be done with it.

 

i had the same problem with my 2000 expy. it was the T-Stat

 

A lot of "Old Schoolers" put a lower value thermostat in as that is what we are familiar with; 160* summer and 185* winter. With these engines we must stick with the factory settings in order to get maximum efficiency from our engines. The wrong thermostat sends the info to the ECU which then tells the fuel and ignition systems what to do and the info it gets will determine the way it runs and the mpg we get.

 

Whatif I keep driving navigator with P0125 code (bad thermostat - temperature low). The heater is working quite fine and gauage shows about 20% above cold. Is there any harm to Engine if I keep driving navigator?

Thanks
John

 

Yes. The engine will stay in open-loop warm-up mode longer than it should. This will waste fuel, raise emissions, and increase the possibility of damaging the cats from excessive raw fuel.

 

It sounds to me as if the thermostat has failed in the open position.

 

If that's the case he is very lucky, I've had 2 that stuck in the closed position and I was fortunate to be close to home and not hurt the engine or blow any gaskets.