I have a 2005 Jetta 2.5 and it seems like one fan runs to fast

temp switch fail most likely. fail safe keeps fan running so engine will not overheat. temp switch will be screwed into engine block. may be cover by cover, hoses or something else but pretty easy to replace. DO COLD for the sensor is in the collant port of the engine and will leak a little when changing. Good luck hope this helps.

run fault codes and look for a faulty fan/ temperature sensor

Replace your thermostat.

probably a rusted out welsh plug

You are talking about the thermo electric cooling fan, its operation is independent of the car's electical system. It is switched on and off by the engine temperature. When you park, the engine heat soaks upward to heat the thermostat turning the fan on. It will run until the engine cools down and the thermostat switches it off. Quite normal operation.

Check that the other fan will run if power applied directly to it.
From wiring diagram, it shows both fans are wired in parrallel- thus should run together.

Hi,

Fan Relay switch is stuck open. This of course assumes your temperature sensor is working appropriately. Which I assumed since you seem to know that the engine is running hot.

Replace the fan relay switch. The relay switch is tripped when the temperature sensor tells the computer the engine is too hot.

Until you get the relay switch replaced, you can either by-pass the relay switch and directly connect the fans to the battery, or turn on your A/C ALL the time and use it at a minimum setting. This will keep the cooling fans running at all times.

Hope i helped you.

Thanks for using ' Fixya ' and have a nice day!!

When A/C is on, both fans should be on all the time. If one is not, probably a dead fan. Replace said fan.

If you have removed the blower motor, Connect it to a 12 volt power supply(your battery)with some jumper wires.It should turn fast, be careful when you connect it, have a good grip on it, it will jump just a little. If it dont run fast its junk. The other 2 things
1)The fan switch
2) The resistor that slows the fan at low speeds.

thermostat replace temp sensor its cheap i hope your water pump is not bad you could mess engine up if you keep on running car and is overheating.