159 2.4 20007 plate
19,500 DPF/EGR by
AO Silver Member
Join Date: May 2009
Location: United Kingdom
Yet another 147 thermostat thread with FES readings.
I think I know where this is going, replacement thermostat, but welcome any other opinions.
My sons 1.6TS is almost never gets to temperature in normal driving, rarely gets above an indicated 80 degrees on the dashboard and the heater is very poor. While I have never had one before, to me, it is also a little thirsty but I suspect he drives it a lot quicker when his parents aren’t in the car and he does short runs.
I have read the threads and absorbed all of the different opinions on dash board gauge accuracy, running temperature, inaccurate sensors and the effect the ECU may have on gauge readings.
So today I have done my own tests with FES and started with a cold car / engine.
Connected FES and took the following readings:-
Engine temp 20°C (strange; air temp is 8°C and showing 7°C on the dash.)
Air temp 20°C (as above.)
Start the car and let it slowly warm up on idle.
FES air temp varied slightly between 20°C and 23°C as the car warmed up. Dashboard air temp readout is solid at 7°C.
FES engine temp slowly rises and dashboard gauge reading is 7 - 8°C above FES until FES gets to 82°C.
Top hose test shows thermostat is NOT bypassing but has opened with FES between 72°C and 75°C. I missed the exact opening point.
With FES showing 82°C car gauge is at 90°C.
NOTE: Car temp gauge remains rock solid at 90°C as FES engine temp readout continues to climb from 82 – 98.5°C.
At 98.5°C the fan cuts in and remains on until FES readout shows 84°C. This was cycled several times and same effect each time.
NOTE: throughout this cycling between 83 and 98.5°C the dashboard gauge is solid at 90°C.
Took the car for a dual carriageway drive and the dashboard gauge rapidly dropped to 80°C with FES showing low 70s.
I got home and repeated all the above tests with the same results.
I also disconnected the sensor on the thermostat - dashboard mounted gauge showed 0°C. FES showed 102.5°C and the engine cooling fan was permanently running (fail safe in event of sensor failure?) Also MIL light on with “Open Circuit” fault against engine temperature sensor.
I cancelled the error with FES and repeated all the above temperature and driving tests with the same result.
The thermostat is not stuck open but is opening early.
The dashboard temperature gauge readout is (despite what so many here have said) overridden by the ECU to give a generally static 90°C thus preventing drivers worrying as temperatures climb towards 100°C. I guess most drivers wouldn’t know that due to the pressurised system cars will not boil at 100°C.
Another possibility is that the sensor is defective but the combined results of the above and inefficient heater makes me think otherwise.
Are there any different opinions or suggestions?
What should I make of the air temperature reading - the car had been driven 3 hours earlier?
Finally, at the risk of corrupting this thread, I noticed with engine at 96°C and idling (847rpm) that the FES “Engine load” showed 20.67%. The FES description of this is “% additional fuel to the basic injection amount calculated from airflow and engine speed. Why would the engine need this additional fuel or do they all show that? I know at idle and with perfect fuel ratios most engines will sound quite rough (well high performance bike engines) - is it just to avoid that effect.