Ford fiesta Mk7 running cool

[Mal3732]

Hi all 

14 plate fiesta 1.0 eco boost not showing any bars on digital temperature gauge when the car is moving, changed coolant temperature sensor and started car idling, checked coolant hoses with thermal image camera and coolant heats up to temperature and 4 bars show on the gauge, problem solved I thought, drove car next day and no bars on gauge and no hot air in car, when car was idling the fan wasn't running so I'm reasonably happy that thermostat isn't stuck open causing fan to run all the time, any ideas would be appreciated 👍 

[unofix]

8 minutes ago, Mal3732 said:

when car was idling the fan wasn't running so I'm reasonably happy that thermostat isn't stuck open causing fan to run all the time,

One of the two thermostats is stuck open.

The fan won't run if you have a stuck open thermostat since the engine will hardly ever reach a high enough temperature for the fan to be switched on. The thermostats don't control the fan, it is a temperature sensor which switches the fan

[Mal3732]

10 minutes ago, unofix said:

One of the two thermostats is stuck open.

The fan won't run if you have a stuck open thermostat since the engine will hardly ever reach a high enough temperature for the fan to be switched on. The thermostats don't control the fan, it is a temperature sensor which switches the fan

Thanks for the reply, how would this relate to the car heating up properly when idling, then when moving, running cool, would cold air flow through the grill be enough to cause the cool running? 

If the thermostat was stuck open then the fan would run constantly or I'm I mistaken, fan is not running as car idles up to temperature 

Thanks again for any input

[unofix]

1 minute ago, Mal3732 said:

the car heating up properly when idling, then when moving, running cool, would cold air flow through the grill be enough to cause the cool running? 

Yes, exactly that. There is no air flow through the radiator when standing still so engine warms up. When moving the air going through the grill is more than enough to cool the engine.

3 minutes ago, Mal3732 said:

If the thermostat was stuck open then the fan would run constantly or I'm I mistaken, fan is not running as car idles up to temperature 

You are mistaken, it is the other way around. A thermostat stuck open means the coolant will not reach temperature and therefore there is no need for the fan to be switched on.

I believe that your engine actually has two thermostats, one located near the top and it is not too bad to change. The other is buried deep down towards the bottom of the engine and in a total nightmare to replace.

[Mal3732]

2 minutes ago, unofix said:

Yes, exactly that. There is no air flow through the radiator when standing still so engine warms up. When moving the air going through the grill is more than enough to cool the engine.

You are mistaken, it is the other way around. A thermostat stuck open means the coolant will not reach temperature and therefore there is no need for the fan to be switched on.

I believe that your engine actually has two thermostats, one located near the top and it is not too bad to change. The other is buried deep down towards the bottom of the engine and in a total nightmare to replace.

Thanks, that makes sense to a point, but if airflow is enough to cool the car when moving why in normal operation should 4 bars be showing on the gauge, and why no hot air from heater? 

[unofix]

2 hours ago, Mal3732 said:

Thanks, that makes sense to a point, but if airflow is enough to cool the car when moving why in normal operation should 4 bars be showing on the gauge, and why no hot air from heater? 

You have a faulty thermostat. I don't know that I can say much more.

[Mal3732]

12 minutes ago, unofix said:

You have a faulty thermostat. I don't know that I can say much more.

Thanks, had a look around the net and you are right, hopefully it is the one next to the coolant sensor, easy to replace, I'll do it next weekend and report back in case it helps anyone else 

Thanks again for the help 👍

[Mal3732]

On 4/17/2022 at 12:47 PM, Mal3732 said:

Thanks, had a look around the net and you are right, hopefully it is the one next to the coolant sensor, easy to replace, I'll do it next weekend and report back in case it helps anyone else 

Thanks again for the help 👍

On 4/17/2022 at 12:47 PM, Mal3732 said:

Thanks, had a look around the net and you are right, hopefully it is the one next to the coolant sensor, easy to replace, I'll do it next weekend and report back in case it helps anyone else 

Thanks again for the help 👍

Hi

Just changed the thermostat on the side of the engine, the easy one, problem solved, car now heats up as it should and holds temperature at steady 4 bars on display. 

Took around an hour to do, little bit fiddly but nothing a semi compotent person couldn't do, thermostat was £16

Thanks again for your help 

[unofix]

3 hours ago, Mal3732 said:

Just changed the thermostat on the side of the engine, the easy one, problem solved

very good to know it's fixed 👍