Ford Fiesta Ecoboost 2014 Not Warming Up/thermostat Reading Wrong

[MJNewton]

Around 90°C at steady state.

 

P.S. Just spotted your username - I was born and bred in Macc!

[turbohater]

My 3 cyl non turbo struggles to warm up when temp is below 4deg outside.When it does reach 4 bars all i have to is dont go over 40 mph,put the heater and blower to max and within a few seconds the temp gauge drops to 2 bars.Done this from new 3 years ago. 

[Micro]

Sat in a garage warming up is much different to running with cool air going past the radiator.

If the thermostat is stuck open, sat still it would still warm up relatively normally. Driving with air past the radiator however would actively cool the engine.

[Maccbrew]

Thanks. This is exactly what is happening. When it's out on a run the engine is cooling down below the optimal temp on the gauge. When it sits in traffic it warms up again. 

Are you suggesting this is caused by the thermostat being stuck open?

[Maccbrew]

Sorry....and if so what problem is this likely to cause?

[Maccbrew]

Another update....

Call from Ford to say they've taken the car out for a drive and the temperature dropped rapidly - not the same behaviour as when it was sat in the workshop.

So this led them to have another look and they've discovered an issue with the thermostat! This is now being replaced under warranty and the car will be back with me tomorrow. 

[Micro]

33 minutes ago, Maccbrew said:

Another update....

Call from Ford to say they've taken the car out for a drive and the temperature dropped rapidly - not the same behaviour as when it was sat in the workshop.

So this led them to have another look and they've discovered an issue with the thermostat! This is now being replaced under warranty and the car will be back with me tomorrow. 

Bingo! ;)

The thermostat keeps the water flowing through the engine until it is warmed up to temperature, at which point it opens (It's a bi-metallic arrangement), allowing a proportion of hot coolant to flow through the radiator to keep the engine at a correct temperature.

If it gets stuck open, then coolant will always flow through the radiator, keeping the engine temperature lower than it should be.

If it was stuck closed, then the engine would overheat when stressed.

[Maccbrew]

Final update. Hopefully this will be useful if someone else has the same issue.

It turns out the thermostat was opening and staying open when it should be opening and closing as it needs to. As described by Micro this was causing the engine to cool down when it shouldn't have but ONLY when it was moving.

Ford have replaced the thermostat (possible the casing too?) under warranty and the issue is resolved. On the return from the garage the engine heated up properly and stayed bang in the middle of the gauge all the way home.

Thanks to those on this forum for their knowledge.