My car over heats after 20-30 minutes heater blows cold a...

Q: My car over heats after 20-30 minutes heater blows cold air and antifreeze is boiling what could it be ? Thermostat ? Or head gask

asked by on January 11, 2018

Recently fixed a misfiring cylinder changed all the spark plugs drove it to work the next morning everything was fine. I came home left the car on for a minute I hear the fan turn on I get in the car park it and I notice the car was over heating. Didnt move it for a few days after that then I moved it again didnt over heat but it took a long time to heat up only heated up to quarter of the way and that took like half and hour drove it around didn't over heat but it never reached the normal temp. Next day I decide I'm going to take it to work turn it on I go inside come out had the heater on but the heater blew cold air and the car again was taking a while to heat up had it on for about 30 minutes I got inside again and when I come out the car is over heating the heater is on but still blowing cold air I turn it off pop the hood and notice the antifreeze is boiling. What can it be ? Thermostat? Or something else ?

Check the coolant level. If the level of coolant is really low, the temperature sensor may not come in contact with the coolant, thus throwing off the temperature reading (it may read cool on the dash gauge but in fact the coolant is boiling and the car is overheating). A low level of coolant, or trapped air, would also explain the no heat condition because there would be inadequate coolant flowing through the heater core. On the other hand, if the coolant level is full, and there is no trapped air in the cooling system, the only way you would get a low operating temperature is if the thermostat is stuck open or the temperature gauge or sending unit is faulty. If the head gasket was faulty and blowing exhaust into the coolant, it would overheat right away. If you desire that this problem be diagnosed by a certified Mechanic, dispatched by YourMechanic right to your location, please request an engine overheating diagnostic and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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