Polo 1.4 CL - Temp gauge never leaves cold, except when standing

Hi Ivette,

Temp sensor/sender units, ussually send a variable earth resistance dependent on temperature, so it sounds like the wiring is broken/rubbed through, causing the sporadic changes due to full earth going to gauge(hot). brocken wire(cold)

But could be a faulty sender just the same, doesnt sound like a thermostat after driving the gauge would still move in relation to engine temp, would start by checking the wiring to temp sensor, also check coolant level and monitor engine temp while driving if gauge is in-op.

Hope this helps.

i would think there is an air lock in the coolant system , have you run the engine whilst at stand still and opened the heater control to the hot position and leave to run for 10 mins or so , let cooldown then check coolant level

This sounds like the temp sending unit for the ecm is bad. There are 2 temp sensors, 1 for the light/gauge and 1 for the ecm. The sensor sends a signal to the ecm to tell it engine temp, the ecm them adjusts fuel mixture for cold or warm engine.This works much the same way as the choke does on a carb for cold starts

If it is actually warm, but the gauage has not moved, you probably have a bad temp sensor that feeds the guage. On some cars there are 2 temp sensors, 1 for the computer to it knows how much fuel to give based on coldness, and one for the guage that just shows you in the dash what the temp is. The other 2 ideas would be a bad gauge and a bad wire/cable from the sensor to the gauge. There is not much else it could be if in fact the reading is wrong.

hey mate
going through similar problem myself right now. 1997 A4 1.8 (same vintage as yours I think)

No heat from vents (luke warm at best) - temp gauge never moves.
I've also been getting really poor fuel economy - I think it is linked to this, as the EMU thinks the engine is constantly cold and changes the air/fuel ratio (like having the choke out when driving).

Q: Does your radiator fan come on when you start your engine from cold? It shouldn't come on until the engine is warmed up. If so your problem could be to do with the fan control unit, or the viscous assembly of the rotor itself. Both can be replaced as one modular unit.

I would be curious to hear what solution you came to as I am troubleshooting this myself at the moment.

The cold start temp sensor is same as ambient air sensor, tells the computer to give the engine a certain amount of fuel to start since there isn't a choke per se. There are two temp sensors, the air temp sensor and the water temperature sending unit usually near the thermostat. The cold start doesn't affect fuel economy unless it's telling the computer the engine is cold. The computer reads several sensors to meter the fuel, map sensor which works off intake manifold pressure (check rubber hose for cracks that connects it), throttle position sensor which is the main fuel control (test it with an ohm meter) and oxygen sensors. The main culprits for bad fuel mileage are usually a partially stopped up catalytic convertor and bad oxygen sensor(s). You can sometimes remove a O2 sensor and spray it with carb cleaner , lightly brush the carbon off with a wire brush to get it working again. This fuel with alcohol is rough on all vehicles. Hope some of this helps.

temp sensors, lambda/oxygen sensor/ reading wrong temp - they would both increasse fuel consumption - have the diagnostics checked at garage.
Air filter, it it clogged or really dirty?
Tyre pressures - make sure they are upto reccomended pressure, (extra pressure reduces rolling resistance and increases fuel economy but at the cost of grip...)
Binding brakes?
Fuel Leak?

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try replacing the sending unit, It is easy but did it when the car is cold

Daughter's R reg VW Polo has heater probs, only just started, fan working fine and temp gauge works normally but only blows cold air. What do you think could be the prob ?

make sure the antifreeze is full. if so, replace thermostat and refill