Radiator fan doesn't come on when overheating

[Tswerie]

Hi, I drive a 2010 1.6 tdi polo hatch, it's currently overheating and the fan doesn't come on (fan comes on when aircon is on).
Is it safe to temporary connect the fan such that it's permanently on?

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[Belix]

Have you checked the termo switch? I don't know the polo personally, but I'd assume it would be on the radiator side. Follow the fan cables to the switch on the radiator. It would be easier than wiring up to permanent power (You do mean only permanent while the car is on, right?)

[Tswerie]

Thanks for the information,

Today I bought and replaced the radiator fan switch. The problem still persistents.

So far I've replaced the water pump, two hoses close to the water pump, thermostat and now the fan switch.

I ruled out a fuse because the fan comes on with aircon. Maybe I should try a auto electrician.

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[J0NN0]

Topic moved to correct section

[Belix]

It's a good idea to try and source the problem with a multimeter first rather than replacing piece one at a time, which can get to be an expensive exercise.
Assuming there is no canbus getting involved here, the wiring should be one loop from battery through radiator switch to a relay, and back to battery.
The second loop would be battery, relay, motor and back to battery.
So first thing I would test is taking a two cable lead directly from the battery positive and negative to the fan plug. The fan may have three pins, in that case one is positive for low speed, one for high speed and the last negative. You can check for the negative pin by checking for resistance or continuity on a multimeter between the plug (not the fan) pins and the negative battery lead. The one that shows no resistance or shows continuity is the negative.
Connect that corresponding pin on the FAN to your lead coming from the negative battery.
Then try both other pins using the lead from the positive battery terminal. It should spin with power on both, but one fast and one slower.
If that works, fan is ok.
Although the switch is new I've had a faulty new switch before.Testing the switch is rather more tricky as it only works when warm enough for each contact to close. It should also have three pins, a negative and two ping for the switches operating at different temperatures, the idea being if things get very hot, the fan better blow at full stick to cool things down. WHen the car is cold there should be no continuity or infinite resistance between the negative pin and both positive pins. At a set temperature, the first switch closes, so you'd have no resistance between negative and one of the positive pins. At the higher temp, the next switch would also close, so no resistance, continuity between negative and the second positive pin.
The last point of failure would then be the relay.
The relay is basically a switch closed by current, so the switch from the radiator fan closes one circuit to the relay, which activates a swtich for the second circuit, between battery and fan.

[Tswerie]

Thanks Belix, I had a auto electrician try and find the fault but no success.

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[Tswerie]

I've noticed that the two pipes connected to the radiator gets very hot but the water in the water bottle is Luke warm.

When the overheating light comes on, I pull over and open the Bonnet and then the water in the water bottle bubbles (boils). When I try to open the lid of the water bottle the water level increases.

I'm thinking the water doesn't circulate untill the water boils.

The car heater also does not work.

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[EX-DOHCTOR]

Have you changed the coolant temp sensor at all?

[Tswerie]

Thanks, yes I did.

So far I replaced waterpump, thermostat, fan switch and temperature switch.
The fan only comes on when the aircon is switched on.

Three possibilities exist that we can think of ,
a) the waterpump might be defective again b) or the radiator might need to be replaced
c) or there is a blockage in cooling system.

A question in my mind,
because the water in the water bottle boils, does it mean that the water pump is working and that their is no blockage in the cooling system?

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[Tswerie]

This morning the car overheating again.

I noticed top radiator hose was hot yet
radiator cold,
water boiling in water bottle and
no hot air from the heater in the car.

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