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have a xsara with a faulty temperture control.driving in devon up and down hills.i notice that the engine gets up to normal temp climbing hills i.e. 90c.but when you go down the hills the temp drops to 70-75c.i think this is a very big differnce considering my air temp at moment is 20c.have changed thermostat and bled cooling system.any thoughts or ideas are welcome.
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I spoke to a Citroen garage yesterday about a similar issue with my ZX. It used to cruise at 90C, higher uphill or in stop/start driving, lower downhill. After a coolant change last year the cruising temp dropped to 75C. Garage did not feel this was a problem in itself, said different coolants can affect temp and that 75C was a reasonable running temp. Also said Citroen temp gauges do tend to fluctuate.
Dave
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As an ex-pilot who relied on one engine to get me around I was VERY alive to engine readings and what you see would worry me! However has it been going on for ever or only just started? If it isn't actually overheating, blowing water out of the header tank and the heater works OK I'd tend to go along with the view that "They are all like that mate" and keep watching the gauge!
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On modern cars with a thermostatically controlled fan, when driving downhill the coolant temperature will tend to drop to the crack-open temperature of the engine coolant thermostat and when driving uphill the temperature will tend to rise above the crack-open temperature until the fan cuts in. Once the coolant has warmed up and reached the crack-open temperature the thermostat will only normally control the lower limit of coolant temperature. I used to see a significant variation in the gauge reading in my 1.9 petrol Volcane.
Armitage Shanks' advice seems sound.
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L\'escargot.
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There is another factor which may play a part in this. At one time fuel injection systems used to shut off fuel supply with a closed throttle and relatively high revs. The fuel was "turned on" again as the revs fell to ensure a smooth transition to idle speed. I suppose it is possible on a long downhill stretch for the coolant temperature to drop simply because there is no heat being produced to keep it warm.
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<< I suppose it is possible ona long downhill stretch for the coolant temperature to drop simply because there is no heat being produced to keep it warm.
This is exactly what happens, although there should be enough heat going into the coolant to keep the temperature up to the thermostat crack-open temperature.
In ganeral, depending on the ambient air temperature and the driving conditions, the coolant temperature can vary anywhere between the thermostat crack-open temperature of, say, 85 degC and a boiling point of about 120 degC.
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L\'escargot.
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I used to worry about temps. on my Fiat because degrees were shown on the gauge,then I remembered my Ford just had blue,white and red-the accuracy was probably similar and bore little relation to actual temperatures.
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There is another factor which may play a part in this. At one time fuel injection systems used to shut off fuel supply with a closed throttle and relatively high revs.
I wouldn't be overly concerned about the running temperatures fluctuating in the way they do. My Polo is precisely the same, always has been. In normal driving, whether it be motorways, hill-climbing or town, 90-92C is the norm. But if I descend a hill, not necessarily a long one, where the engine is left to do the braking, then the engine temperature can drop by about 10 degrees. This is mainly due to the car having an overrun cut-off, so when descending the hill there is no (very little) fuel being fed to the engine to burn. Only if this behavior is new, should you need to have it looked at.
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I wouldn't be overly concerned about the running temperatures fluctuating in the way they do. My Polo is precisely the same, always has been. In normal driving, whether it be motorways, hill-climbing or town, 90-92C is the norm. But if I descend a hill, not necessarily a long one, where the engine is left to do the braking, then the engine temperature can drop by about 10 degrees. This is mainly due to the car having an overrun cut-off, so when descending the hill there is no (very little) fuel being fed to the engine to burn. Only if this behavior is new, should you need to have it looked at.
Our Fiesta does this as well. Can't tell the temperature fluctation as there are no calibrations on the gauge, but the gauge drops back slightly when going down a long hill. There's one on the M3 particularly that always causes it.
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bought car two months ago and have covered 3000 miles and had to replace thermostat.it had snapped on spring holder and could bearly get warm.i.e. no reading on temp gauge.replaced themostat then found out how hard it is to bleed system so off to citroen i went.heater does not work correctly unless on max heat and fan on at least half speed.cannot get cold air to blow through system.always luke warm.heater will turn its self on and off at will regardless of road speed,outside air temp,fan speed,heater setting below max,etc etc.but engine temp only varies on hills heater on or off makes no difference
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