so im kinda stumped. i put on a new timing belt kit last weekend and since my coolant gauge never worked i made sure i put the thermostat in. and it still did not work. so then yesterday my coolant temp sensor came in and i put that in and what do you know my gauge still does not work right. it seams every time i cold start my car the coolant gauge will work untill it gets to the normal temp and then it will just drop all the way back to the cool side. my oil temp is up around 200F and the heater still blows hotter then hell so i dont think its the Tstat andi made sure that the sensor is pluged in good. so what the hells going o guys? bad brand new sensor?

 

a bad new sensor would be my guess or an electrical break somewhere, if anything id try to replace the ECt since you can still return as a defective item so it wouldnt hurt to try.