1996 Chevy Blazer no heat blows cold air temp gauge as high 150 only when running coolant levels fine?

Answer 1

You may have air trapped in the coolant lines. Remove the radiator cap when COLD, start your engine and let it run and watch inside the cap opening for coolant to start circulating. If you see air bubbles coming to the surface, you have trapped air and the coolant level will go down as coolant begins to replace the trapped air. Keep the engine running to operating temp letting the coolant completely recycle throughout the engine and heater. Once you have the air out top off the radiator. If you do nto have trapped air in the coolant, then your thermostat is tuck in the OPEN position and the coolant is being recirculated too quickly and is not being held in the engie to heat up via the thermostat. Check for trapped air first, and then move onto the thermostats. Most thermostats stick in the CLOSED position and this is why engines overheat, not allowing the coolant to flow to the radiator to be cooled. Yours may be the opposite. Or maybe there isn't even a thermostat in there......soem peopel remove them when they begin to have overheating problems thinking this may help which it doesn't. And one other factor, make sure you have a good radiator cap with the correct pressure. Look at the underside of the radiator cap at the rubber seal and make sure it is soft and clean any junk under the cap be it around the spring or lip. A good radiator system works best under pressure.