Expert: Sean Halliday - 1/24/2008

Question
1990 Nissan Maxima, V6, 5 Speed, The temperature gauge would read cold and the heater would run cold so I replaced the thermostat and filled the coolant. In the morning I let the car idle for about 15 minutes and the temperature gauge went about half way, I started driving the car and when I got on the highway the temperature Gauge went back down to the cold and the heater started blowing cold. From what i've read my guess would be the next to replace is the coolant temp sensor. I know this might seem dumb but where is located?

Answer
First off,did the coolant level drop?Thats after you were on the freeway.Check the coolant level again before you buy any new parts.Usually the temp sensor is on the thermostat housing,or close to it.If the sensor isnt working,it would not make the heater run cold.It sounds like you have a major coolant leak or blown head gasket.