hi guys, can some one please tell me what is the sensor on the right?
and the sensor on the left is the temp sender unit? am i right?

 

Picture 1 is the engine coolant temp sensor for the ecu. The other is the engine temp sending unit for the guage.

 

let me just this straight, the one to the gauge is the one sitting between the exhaust manifold? and the one near the thermostat is the one for the ecu?

 

Precisely as I stated.

 

ok, thanks.
now i knoe one which one i should focus - the gauge was suddenly shot up and stayed there. not at the hottest point but at the rightest point, and i can't understand why..
I've tried to ground the wire but it didn't help..

 

What year is the vehicle? I know in my '86 K5 I've had to replace 3 gauages over the course of 25 years (oil, temp and fuel) - apparently they burn out despite the sensors being ok. You may want to check them....

 

If you ground a single point gauge connection at the sensor, the gauge should read high. Unhooked should read bottom of scale.

If it does that, your sensor is bad. If it stays high gauge is bad or wire is shorted somewhere.