Is the main coolant fan supposed to be on as soon as engine is started cold? 2.5 tdi

[Tommy5150]

Hey guys,

Just wondering if anyone know if the main cooling fan on radiator is supposed to turn on as soon as engine is started (cold)? Or if that fan runs all the time? It's the big one on the left that cools radiator. Wondering if it's supposed to be like that or if I have to change coolant temp sensor maybe?

2005 A4 B7 Avant 2.5 TDI BDG

Engine runs fine otherwise and fan turns off as soon as car is switched off and does not run when car is off, no water in ECU and relays all good. VCDS clean no fault codes.

Just wondering if anyone knows if it's supposed to be like that or if there is some sort of fault with temp sensor? As far as I know this car only has the one 4 pin coolant temp sensor which communicates with the ECU that is on the top of the engine.

Couldn't find anything online about this if it's supposed to run all the time with engine on.

Small AC fan is off until AC is turned on so that's fine. Just not sure about the main one.

Is the number 45 another coolant temp sensor? (from the pic below at the very bottom) It is blacked out so not sure if it's there and right now it's raining so thought I'd check this here if anyone knows.



Many thanks.

Tommy

[80sGuy]

No, the fan should NOT be blowing right away at cold starts unless it is needed to like: if your engine temp is climbing and needs cooling. When my coolant temp sensor plug housing broke my fans started to blow excessively high at all times until I shut the car off. This will screw up your ecu giving false readings telling the fan and engine to work harder. So my bet would be a faulty Coolant temp Sensor.

[Tommy5150]

No, the fan should NOT be blowing right away at cold starts unless it is needed to like: if your engine temp is climbing and needs cooling. When my coolant temp sensor plug housing broke my fans started to blow excessively high at all times until I shut the car off. This will screw up your ecu giving false readings telling the fan and engine to work harder. So my bet would be a faulty Coolant temp Sensor.

Hey 80sGuy,

Thanks heaps for you help. Though so just wasn't sure. Don't really know these TDI engines too well always had Gas so just wanted to make sure. Because the Fan on the 2.5 TDI is not free standing and powered from within like on Gas engines but from a pulley bolt from the engine side. That's why I was not sure if it's always supposed to be on.

Other than that the old coolant temp sensor displays the correct temperature and does not drop of or fluctuate that why I was thinking I'm not sure it is bad, and that VCDS did not log any coolant temp sensor faults. Will change the coolant temp sensor and see what happens. Do you know if this engine only has the one or is there a second at the bottom? and if so which one do I change?

[80sGuy]

I only know of one located/attached to the rear coolant flange by the firewall.

[Tommy5150]

ok cool. My BDG engine has it at the front top of the engine. Like in the pic attached above #35

[80sGuy]

Well that looks MUCH easier than the ones we have on the back.

[Tommy5150]

Well that looks MUCH easier than the ones we have on the back.

yeah I can imagine it is

[Theiceman]

well if that fan is coupled to the crank via a pulley i would expect it to run all the time .
of course some have viscous couplers, but it sounds like a mechanical driven fan, not an electric based on description.

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[Tommy5150]

well if that fan is coupled to the crank via a pulley i would expect it to run all the time .
of course some have viscous couplers, but it sounds like a mechanical driven fan, not an electric based on description.

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Hey Iceman,

yeah I kinda thought that too but wasn't sure.... Here is a pic of it. There is no motor inside the fan

The top is where it comes out of the engine side, the bottom is the radiator side.