The heater blows cold air. I replaced the thermostat, which was stuck open, now the enigine runs at full temp but still no heat and when looking in the coolant resvoir, the coolant does not appear to be circulating. The top rad hose is very hot but the bottom hose is cold. Wouldnt the engine overheat if the collant was not circulating? 2001 Silverado 1500, 4.8
Yes it would overheat without circulation, but the coolant doesn't circulate through the overflow tank. That reservoir only gets coolant into it when the coolant gets hot and expands and pushes the radiator cap seal up to let coolant into the reservoir. When the vehicle cools down, the coolant contracts and the lower level in the radiator will siphon the coolant out of the reservoir back into the radiator. Coolant circulation is from the engine to the radiator and back into the engine...and also through the heater core.
You may have an air block in the heater core. Check by taking off the outlet hose at the firewall or at the engine and see if you have a slow steady stream of coolant, with the engine running and heater controls on high heat. If it was an air block, a steady stream should quickly start. If you get little or no flow, the core may be plugged and need flushing backward or replaced.
Testimonial: "Thanks for your response. I took it in to be looked at today. Hopefully it will not be too expensive to fix. I guess it's safe to assume that the rad and water pump is working since the engine never has over heated. I am hoping it is just the blend door or a blockage like you say or something like that. I have a very good mechanic looking at it today, i will let you know what ends up being the solution. "
SOURCE: 04 civic heater blows cold air at idle
you should have hot water on all rad. hoses when the motor is running at a norm. temp. the water is not going through the heater core like it should. you have cutoff valve bad low water are a stopped heater.try a hoter thermostat if none of the above are true.
SOURCE: 1994 2.3 lt grand am. i have replaced the water
change the upper hose and if thats no good change your radiater it maybe no good with this car it happens alot
SOURCE: 2006 Pontiac Torrent heater blowing cold air
hi
check the heater hoses and if both are hot then the mode door is broken
i have replaced 2 in the torrents(not a nice job)
SOURCE: new thermostat,waterpump,coolant,block flushed rad
take the thermostat out and heat it up in a pan of water to see if it will open when it gets hot.
you should see it open when it gets hot.use a cooking thermometer to watch the temp. it should open between 180 and 225 deg.
SOURCE: 1990 toyota corolla wagon 1.6 liter 5 spd. overheating
you've got a possible blockage in the head or block.
Air
Temperature Control Blend Door Failure No Heat or no AC (dependes on
where door sticks)
In
all modern cars there is a tiny DC electric motor driven gear drive
that moves a plastic door that blends heated and cooled air from the
AC and the heater core, this is called (interestedly enough) the air
temperature control blend door actuator. The motor that moves this
door fails because the door starts sticking from warping, most common
complaint is no heat but it can be no AC as well. To replace these
parts (blend door and blend door actuator) you must remove the entire
dash from the car. Always have this problem confirmed by a dealer or
qualified repair shop as it is a very expensive repair.
Other causes of no heat in the cabin are engine thermostats that are stuck open (engine runs cold) or air bubbles in the cooling system.
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