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Discussion Starter #1
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.

My conclusions:-

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.

Questions:-

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.
 
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right the temp sensor has 2 elements, one reports to the ecu, the other to the dash guage. if you are happy that the ecu is seeing the correct temps, then ignore the dash guage.
 

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Discussion Starter #4
Dave, I read that thread and did that test. My results both agree with and contradict its findings.

The thermostat is opening in one go, not stuck, but I am convinced it is opening early. I also believe the dashboard display is over-ridden by the ECU to be static at 90 for any engine temperature between 83 and 98.

These are concluded from what FES and the heater efficiency is telling me.

Yes I know it's long but wanted to show that I had read the threads and considered all options. Bit like an old women me - why use 1 word when I can use a sentence.
 

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Dave, I read that thread and did that test. My results both agree with and contradict its findings.

The thermostat is opening in one go, not stuck, but I am convinced it is opening early. I also believe the dashboard display is over-ridden by the ECU to be static at 90 for any engine temperature between 83 and 98.

These are concluded from what FES and the heater efficiency is telling me.

Yes I know it's long but wanted to show that I had read the threads and considered all options. Bit like an old women me - why use 1 word when I can use a sentence.
what temp is it opening at (feeling top hose) on FES?
 

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Discussion Starter #6
Lacken: that leads me to replace the thermostat. FES shows it is holding 70-73 on a dual carriageway run and the heater efficiency reinforces that.

That shows a simple top hose test is NOT a guarantee of correct function of the thermostat. Opening in a single go and not stuck open: yes. Opening at correct temperature: no.
 

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Discussion Starter #7
Dave: read the thread - no that's arrogant from a novice.
Somewhere between 72 and 75. I missed the exact point.
 

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Dave: That is what I thought. The interesting bit is that this shows that the top hose test is not a guarantee of correct thermostat opening and so many people go back to the thread that you pointed out. It was also my starting point and one I have used for years.

I think that it's also interesting that, if they are all the same, the dash gauge between 50 - 82°C reads 7-8 degrees high. So a top hose test with dash readout on 80 might make someone think the stat is working correctly meaning they will have an engine running temperature of low 70s.

Not only is that wasting fuel but it is outside the optimum operating temperature for the engine oil.
 

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Dave: That is what I thought. The interesting bit is that this shows that the top hose test is not a guarantee of correct thermostat opening and so many people go back to the thread that you pointed out. It was also my starting point and one I have used for years.

I think that it's also interesting that, if they are all the same, the dash gauge between 50 - 82°C reads 7-8 degrees high. So a top hose test with dash readout on 80 might make someone think the stat is working correctly meaning they will have an engine running temperature of low 70s.

Not only is that wasting fuel but it is outside the optimum operating temperature for the engine oil.
true but not everyone has ecu software though :) and would you pay a garage 1 hrs labour to find out?
 

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Discussion Starter #11
No and I would add that I wouldn't pay a garage a penny but in my old age I do get lazy. Especially when it's cold outside and the alternative is alcohol!
 
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if on the open road the ECu is seening 75 to 75 degs, then coolant is by-passing the seal of the stat, replace the stat.
 
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