Normal fuel temperature on 2.7 HDI ?itroen C6

[raboten9]

Hello.
It concerns a Citroen C6, 2.7 HDI, 2007.
I installed an Android app called FAP for Citroen and Peugeot.
A few days ago I noticed that the fuel temperature was flashing red after a long drive. At departure, the ambient temperature is normal - about 25 degrees and it is in green. After 5-8 km it becomes about 52 degrees and lights up orange. After another 10-15 km, it's already in the red and it's 85-93 degrees.

Is this fuel temperature normal? About 90 degrees.

If not, can anyone give an idea what the problem is?

[MGmike]

I guess it all depends on where the temperature is measured. Do you know?
There is a heater/cooler as part of the oil filter housing which will heat/cool to coolant temp which is usually around the 90deg point under normal operating conditions. There's also a cooler under the floor in the return line before fuel drops back in the tank.

Without knowing where the temp is measured it's all guesswork as to what it should be.

[GiveMeABreak]

The fuel heater operates in ambient temperatures from very cold up to around 50°C.
The fuel heating function works on the principle of re-circulation of the diesel fuel by the thermostatic valve.

There's not much else about the function, apart from the cooling function where the high pressure pump creates turbulence in the fuel thus causing the temperature of the fuel to rise.
The fuel cooler cools the fuel as it returns to the tank.

[Rp0thejester]

I have never heard of any issues of having a high fuel temperature on any vehicle. I'd imagine it's normal as if the car was in Dubai I would expect high fuel temperatures. And I've certainly never heard of an app to monitor it, I'm sure NASA will have one though...

[MGmike]

The fuel heater operates in ambient temperatures from very cold up to around 50°C.
The fuel heating function works on the principle of re-circulation of the diesel fuel by the thermostatic valve.

There's not much else about the function, apart from the cooling function where the high pressure pump creates turbulence in the fuel thus causing the temperature of the fuel to rise.
The fuel cooler cools the fuel as it returns to the tank.

Thanks Marc. I don't suppose you know where the ecu would get a fuel temperature measurement from?

[GiveMeABreak]

Sure:

Fuel Temperature Sensor

Shown at (44).

Role of the diesel injection ECU as a function of the information received:

• To adjust the fuel flow
• To calculate the fuel density

The fuel temperature sensor (44) comprises an NTC (negative temperature coefficient) element.
The more the temperature increases, the more its resistance value is reduced.

Fuel temperature (°C)	Minimum resistance in ohms	Output voltage
20	6200	4,4 Volts
40	2600	3,6 Volts

[raboten9]

Thanks. Looking at where the sensor is located, it is normal for the temperature to be around 90 degrees. But there is also a fuel cooler underneath, as I looked at the diagram, the fuel is under the passenger seat. I need to check if it cools the fuel that goes back into the tank. One of these days I will look down at her and check.

[GiveMeABreak]

Here:

[MGmike]

Sure:

Fuel Temperature Sensor


Shown at (44).

Role of the diesel injection ECU as a function of the information received:

• To adjust the fuel flow
• To calculate the fuel density

The fuel temperature sensor (44) comprises an NTC (negative temperature coefficient) element.
The more the temperature increases, the more its resistance value is reduced.

Fuel temperature (°C)	Minimum resistance in ohms	Output voltage
20	6200	4,4 Volts
40	2600	3,6 Volts

Thanks Marc.
One last question... where's the thermostat that controls the temperature to 50Deg mentioned in a previous post, is it part of the heater unit mounted on the oil filter housing?

Is that two questions

[GiveMeABreak]

There’s nothing else about that function I can see Mike.

[MGmike]

There’s nothing else about that function I can see Mike.

Thanks Marc.

raboten9,
from the info Marc has provided it would appear you have either a senor fault or, more likely, a fuel heater fault!
I would change the sensor first as that's easy to get to. If you can't find a new one DM me and I'll sell you a used one. If it still shows high after replacing, you'll need to think about the fuel heater unit but that's probably going to be a whole lot of pain....

[raboten9]

Thank you for the information. I found out about the fuel sensor and will try to replace it. But I haven't figured out where this fuel heater is and what the NORMAL OPERATING temperature of the fuel is that I need to achieve. 50 degrees?