KA Temp Guage Sensor

[jdm2191]

Ok my S14 KA latly has been overheating!

I Already....
-changed the thermostat
-check to make sure I have a good head gasket
-fresh radiator fluid/bled the system
-checked my radiator (no leaks)
-tested 2 different radiator caps (to check if it still overheats)
-fresh oil in my motor
-changed my temp sensor ground

But what it's been doing is jumping staight to the "H" after about driving like 5mins or less...it goes a little over half at first then jumps all the way up? What makes me think it's my temp guage sensor is that motor doesn't act like it over heats?

My motor still has power my clutch fan is blowing cold air, not hot air? It's not showing signs of overheating?

So my friend with his software on his computer hooked up my car to his computer & it read my car 240 degrees!! But my car was idleing fine/blowing cool air?

So can the Temp guage be bad & basically be lieing to me about the tempeture but really be at regular operating tempature?