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MY car suddenly started over heating97 Jetta trek 2.0. one day its fine the next day it overheats in 5 mins of driving

I checked some forums to diagnose whether its water pump, thermostat, fans, or fuses

Fans do not turn on, even when hot. fuse by coolant reservoir is good. There is flow in coolant reservoir when hot, and upper hose from radiator gets hot indicating there is flow

One thing that is weird, and is not mentioned in the other forums, is when the car is cool the engine temp gauge reads 180. My car hasn't been started for days, its in the garage out of the sun, and its only 70 degrees outside. But when I put the key in and put it in the on position without even starting it, the gauge jumps up to almost halfway. Which is around 180.

I am very confused about this. does that mean its the thermostat?
 

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On a 2.0 the upper rad hose will get hot no matter what. Its ambient temp exchange because its at the top of the head. To test weather the T stat is open or not you want to feel the lower rad hose. If both hoses and the rad are getting nice and hot but no fan you need to check the fan working backwards.

If you have AC does the fan come on when you turn the AC on? Also if you have the AC fan on does the engine still overheat? If it does you have more than one issue. If no AC Jump the fan directly to the battery. Does it turn on? If no suspect a dead fan. If yes jump power into the relay imput from the thermo fan switch in the lower drivers side of the rad. The relay is on the fan shroud usually. If no suspect a bad relay, If yes first check the connector between the thermo switch and relay for corrosion. Then suspect the Thermo temp switch.

Its very easy to test the switch while in the rad still. Rig up so with the connection still on you can plug your multi meter or test light to the output wire going to the relay and the other to a ground. And then get the car hot. If it starts to get warm enough that its early over heating and still no voltage out of the temp switch its dead.
 

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jeremyK "My car hasn't been started for days, its in the garage out of the sun, and its only 70 degrees outside. But when I put the key in and put it in the on position without even starting it, the gauge jumps up to almost halfway. Which is around 180."

If engine is cold, hasn't been started in last 6 hours, when you turn the key to the on position & gauge is halfway before you start it.
There is something wrong with the gauge, if the gauge starts reading in the center before you start it
by the time engine warms up to running temp the gauge will reading past 360 degrees.

If the engine would run that HOT it would be boiling the coolant out of the coolant bubble.
 
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