WZ Ecoboost not getting up to temp

[Ben228]

Had this problem for a little while now.

Essentially, the car (1.0 Turbo Fiesta Sport) is not getting up to operating temp (generally 0 bars on the temp indication on the dash), also I'll only get cool-ish air through the heater.

Occasionally when it's warm/in traffic/driving up some hills I'll see 2/3/4 bars of temp (and the heater will blow warm-hot air), as soon as the load is off the engine it'll quickly lose the bars (and the heater will slowly go back to blowing ambient air).

For me, the obvious answer was one (or both) of the thermostats is stuck open.
Ordered (both genuine) a block thermostat and main thermostat.
Replaced them both (tested old ones which turned out to be serviceable, but given I had new ones replaced them anyway).
Problem is still exactly the same. Did not fix.

I bench tested the Coolant Temp Sensor just in case. At cold I had a resistance of 30K Ohms, and the resistance decreased as I applied heat, so I THINK the Coolant Temp Sensor is fine?
But as far as I know, it's the only other thing in the system I haven't replaced.

I'm out of ideas now.
Any suggestions?

Thanks in advance!

EDIT: I should also add, no codes are being thrown either.

[russellw]

You could also check the Cylinder Head Temp sender (CHT) as it's the main input for the ECU.

The values for the ECT are as follows:

0^oC = 4.14V / 95.85 kΩ
10^oC = 3.73V / 57.85 kΩ
20^oC = 3.26V / 38.30 kΩ
30^oC = 2.74V / 24.27 kΩ
40^oC = 2.23V / 16.15 kΩ
50^oC = 1.77V / 10.97 kΩ
60^oC = 1.37V / 7.70 kΩ
70^oC = 1.05V / 5.37 kΩ
80^oC = 0.80V / 3.84 kΩ
90^oC = 0.61V / 2.80 kΩ
100^oC = 0.47V / 2.07 kΩ
110^oC = 0.36V / 1.55 kΩ

[Ben228]

Originally Posted by russellw

You could also check the Cylinder Head Temp sender (CHT) as it's the main input for the ECU.

The values for the ECT are as follows:

0^oC = 4.14V / 95.85 kΩ
10^oC = 3.73V / 57.85 kΩ
20^oC = 3.26V / 38.30 kΩ
30^oC = 2.74V / 24.27 kΩ
40^oC = 2.23V / 16.15 kΩ
50^oC = 1.77V / 10.97 kΩ
60^oC = 1.37V / 7.70 kΩ
70^oC = 1.05V / 5.37 kΩ
80^oC = 0.80V / 3.84 kΩ
90^oC = 0.61V / 2.80 kΩ
100^oC = 0.47V / 2.07 kΩ
110^oC = 0.36V / 1.55 kΩ

Thanks for your reply!
I'm happy that the Coolant Temp Sensor values are within tolerance, given it was about 25° C ambient when I got the 30kOhms.

How do I access and test the CHT sender?
It's a 2016 model if that makes any difference.

[russellw]

Not sure if it has one as some models with an ECT don't and even though I have specs for a CHT sensor on the 1.0 EcoBoost it doesn't seem to be used in all instances where the engine is used. If it has one it will be directly mounted to the cylinder head - have a look at THIS YouTube video. If it has one let me know and I'll get you the reference values for it.

The cooling system itself (now that I've read the manual) is quite complex.

The cooling system is controlled in 3 phases.

Phase 1
When the engine is cold, the small/large coolant circuit thermostat and the short block thermostat are closed. The mechanical coolant pump delivers the coolant only to the exhaust-side part of the cylinder head. In this phase, the coolant in the coolant jacket around the cylinder and in the intake-side part of the cylinder head remains motionless. Below a coolant temperature of approximately 70°C and below an engine speed of approximately 3000 rpm, only the exhaust-side part of the cylinder head is cooled. The coolant flows from the part of the cylinder head on the exhaust side into the thermostat housing in the small/large coolant circuit and bypass valve and, from there, via the heater core to the oil cooler and then back to the coolant pump.
In addition, part of the coolant flows from the short block through the electrical coolant pump and, from there, on past the exhaust gas turbocharger to the coolant expansion tank and then back to the coolant pump. Below a coolant temperature of approximately 70°C and below an engine speed of approximately 3000 rpm, the small/large coolant circuit thermostat and the bypass valve are closed.

If the engine speed exceeds approximately 3000 rpm, the bypass valve opens. The now increased coolant pressure from the engine opens the bypass valve so that the increase pressure can escape directly to the intake side of the coolant pump.

I think that last paragraph might be a clue as if the system isn't pressurised correctly, I assume it can't open the bypass valve.

Phase 2
The short block thermostat opens at a coolant temperature of 70 °C and is completely open at 85 °C. As with a conventional system, this opens the small coolant circuit.
The coolant pump now also delivers the coolant to the cooling jacket around the cylinder, washes around it and enters the entire cylinder head via the bore holes.

Phase 3
The small/large coolant circuit thermostat opens at a coolant temperature of 92 °C and is completely open at 106 °C. At the same time, the bypass valve thermostat closes. This ensures that the entire coolant flow, regardless of the coolant pressure, is always routed via the radiator.

Might pay to actually check the radiator water temperature using an IR temp gauge to see whether it is actually heating up or just circulating all the time - I suspect the latter with the thermostats both open but I'm guessing here.

[Ben228]

I've had a look through both the onboard diagnostic menu and and OBD2 scanner and the water temp after a 10 minute drive is being shown as high 50s-low 60s (Degrees C).

I've had a look at that video and mine definitely has the Coolant Temp Sensor like that one.
I'll suss out how much a replacement one is and if they're not too expensive, I'll replace it and see what happens.