Has anyone noticed how quickly the car gets to temp? It doesn’t go past the halfway point and overheat. But it does get to temp fast.
The engine is relatively small, so it won’t take as long to reach operating temperature compared to larger engines. Also, the temperature gauge is based on coolant temperature, so the oil may still not be up to temp even when the gauge is in the middle.
From memory, the midway point on the gauge can be anywhere between 80 to 120 degrees Celsius, which is a huge range. The gauge is not linear, so it can be misleading. An OBD2 device will give you the actual temperature reading!
The range for the middle point is even worse than I thought. I’m not sure of the exact figure, but I’ve definitely seen the gauge at half while my OBD reads 55°C.
Once it goes past half, though, you should definitely be concerned about the engine and take immediate action to cool it down.
I personally overheated during a track day after one of the two small coolant return hoses leaked (the one from behind the engine head, not the turbo return). I nearly lost all coolant and only realized when the car went into limp mode, with all bars lit up. From the time I noticed until I plugged in my OBD reader, there was probably a solid 5 minutes. The coolant temp sensor still read 130°C. I’m not sure how hot it actually got, but I was lucky the damage wasn’t worse—only needed a head surface of 2 thousandths.
The cooling system has bypass valves which effectively bypass the radiator completely. The service manual states:
Engine Cooling - System Operation and Component Description
System Operation
Engine coolant flows primarily from the engine to the radiator circuit and back to the coolant pump. Coolant is sent from the coolant pump through the engine block and cylinder heads. A separate circuit from the engine also feeds the heater core and turbochargers with coolant. The coolant pump, operated by engine rotation through the accessory drive belt, circulates the coolant. The coolant thermostat is a control valve actuated by coolant temperature. When the thermostat is closed, coolant flow bypasses the radiator circuit and returns to the coolant pump. When the thermostat is opened, coolant flows through the radiator circuit to transfer engine-generated heat to the outside air.
The degas bottle holds surplus coolant and removes air from the cooling system. It also allows for coolant expansion and system pressurization, replenishes coolant to the cooling system and serves as the location for service fill.
The thermostat monitor is a function of the PCM and is designed to verify correct thermostat operation. The monitor executes once per drive cycle and has a monitor run duration of 300-800 seconds. If a malfunction occurs, DTC P0125 or P0128 sets, and the MIL illuminates.
The engine’s cooling circuit consists of an additional coolant bypass solenoid valve and coolant shutoff solenoid valve. Using these two valves, the coolant flow through the engine is specifically restricted or stagnated in the warm-up phase. This restriction of the coolant flow makes it possible for the engine components to warm up faster. The result is a significant reduction in the emissions of harmful pollutants and an improvement in fuel economy (i.e. reduced friction) during the warm-up phase. Both solenoid valves are controlled by the PCM.
The following input parameters are used to do this:
Coolant temperature
Ambient air temperature
Engine speed
Engine load
Status of the air conditioning system
Warm-up regulation is performed in four phases. Phase 1 or 2 occurs after initial engine start-up depending on the ambient air temperature.
Phase 1:
During an initial engine start-up with an ambient temperature is 60-75F (16-24C) or warmer (calibratable) the coolant shutoff solenoid valve closes and the coolant bypass solenoid valve remains closed. With both valves closed the coolant is stagnant and does not circulate in the engine (cylinder block and cylinder head) or through any other cooling system component to significantly decrease the engine warm up time. This reduces emissions and fuel consumption during warm-up.
Phase 2:
During an initial start-up with an ambient temperature 60-75F (16-24C) or cooler (calibratable) the coolant shutoff solenoid valve remains open. This allows engine coolant to circulate through the heater core providing cabin heat to the customer. When the coolant shutoff solenoid valve is open, the coolant circulates through the engine (cylinder block and cylinder head), heater core, engine oil cooler, transmission oil cooler, turbo, and degas bottle. Coolant is also routed into the thermostat housing which initiates the warm-up phase of the thermostat.
Phase 3:
The coolant bypass solenoid valve is energized and opens when engine coolant reaches (158F) 70C and the engine load is greater than 70% or engine speed is greater than 4,000rpm. When the coolant bypass solenoid valve opens coolant is routed through a coolant between the engine block output and thermostat housing. The opening of this coolant circuit increases the coolant flow rate through the engine block which reduces cooling system pressure and temperature fluctuations in the engine block.
Phase 4:
At about (194F) 90C, the thermostat opens and the coolant is routed through the radiator. However, the thermostat opening temperature is partially variable via the coolant bypass solenoid valve. The temperature around the thermostat and its expansion element is the total of the coolant temperatures entering the thermostat housing. Targeted actuation of the coolant bypass solenoid valve allows increased flow of coolant from the engine block to contact the thermostat element and allows an actual coolant temperature of between (194F) 90C and (212F) 100C to be set.
In my Fiesta, it reaches halfway (4 bars) very quickly. But when I check the OBD data, I can see that halfway is only 50°C. I have a UK-spec car, so I’m not sure if this is different in other regions, but I’ve confirmed it in two other cars as well. It will still take a few more minutes to reach the proper operating temperature, which seems to be around 82-85°C. Keep in mind, the oil may take a bit longer to warm up fully.
Agreed, it heats up quickly. The small aluminum engine and head in a compact compartment, especially with the turbo at the back, definitely contribute to how fast it reaches temperature. I’m impressed with how quickly it warms up too—it’s a nice feature, especially when you’re eager to get the car running at optimal temps.
The stock radiator really is inadequate—it’s super thin, only about half an inch thick. Switching to an aluminum radiator is definitely a smart move. I had mine overheat within the first week at 40k miles, but once I installed the Mountune radiator, it handled the heat, especially in AZ weather, like a champ. It makes a huge difference in keeping things cool under harsh conditions.