extraduty

Changed out the thermostat on a 2000 chevy silverado and now have no heat. If I have the radiator cap off and the engine running, I do get some heat but it doesn't last long.

Is there a valve somewhere in the system to bleed out the air?

Thanks,
Don

in2pro

Was it working prior to the thermo change?

can you feel the lines to the heater core are they getting warm/hot?

for the heater it should not matter but is the thermostat in upside down?

The air in the system should purge itself after a drive cycle or so, is the over flow tank staying filled?

Did you flush the system or just replace thermostat, is it possible gasket material got into the system?

Is the temp gauge going to normal and can you see the thermostat operate
via the temp gauge?

Just some thoughts of things to check

extraduty

Was it working prior to the thermo change? No, That is why I changed the thermostat to begin with.

can you feel the lines to the heater core are they getting warm/hot? Yes, more so if I squeeze the hoses while it is idling with the cap off which leads me to believe there is still air in the system.

for the heater it should not matter but is the thermostat in upside down? Thermostat and housing came as a single piece, so no it is not backwards.

The air in the system should purge itself after a drive cycle or so, is the over flow tank staying filled? Overflow tank is staying full.

Did you flush the system or just replace thermostat, is it possible gasket material got into the system? Just replaced the thermostat as well as drain and replace antifreeze. Don't think gasket material got into the system especially because of the thermostat location being on the side.

Is the temp gauge going to normal and can you see the thermostat operate via the temp gauge? Temp gauge is going to normal temps. The thermostat seems to be working properly

in2pro

When you turn the heat on and put it on high do you feel the air coming out of the vents?

If no, then the actuator that opens the baffle door is not working.

if yes, then the heater core is probably blocked and needs to be reverse flushed or just replaced...

do both the heater core lines feel warm/hot or one more then the other?

if they are very different in temp then the core is blocked or plugged

If the green anti-freeze was ever added to the pink or orange anti-freeze
then you have a nice cheezy build up in the system and that is probably is what is clogging up the core.

extraduty

When you turn the heat on and put it on high do you feel the air coming out of the vents? Yes. It is actually warm on occasion (when the cap is off)

If no, then the actuator that opens the baffle door is not working.

if yes, then the heater core is probably blocked and needs to be reverse flushed or just replaced... Probably need to take it to someone with the equipment to flush it properly.

do both the heater core lines feel warm/hot or one more then the other? I will check this afternoon

if they are very different in temp then the core is blocked or plugged

If the green anti-freeze was ever added to the pink or orange anti-freeze
then you have a nice cheezy build up in the system and that is probably is what is clogging up the core. Flushed and refilled with Dexcool (at the 5 year mark) nothing but dexcool ever added.

extraduty

How would I be able to tell if the "doors" are opening and closing correctly?

in2pro

if you feel the air blowing out and it feels like it should (except for temp) being blown out if you had the blower on high then the actuator is probably working correctly, but if you put it on high and there is really not a lot of air blowing down where the heat should be coming from then its not opening correctly....

as for flushing it, if you can get to both ends of the heater core hoses you can try flushing it with the water hose just don't put too much pressure behind it...
it might be easier to price the core and replace it thou...

as for it acting different when the radiator cap is off or on, not sure on that one... the radiator cap controls the pressure only a bit to help control the boiling point of the coolant and allows excess to bleed off into the over flow when hot and the opposite as it cools....

if you were seeing any over heating I would suspect a worn water pump but you only seeing a heating environmental issue, so I would focus on the heater core or the air flow control...

and I have seen both issues in this forum so its 50-50 but seeing what you see on the air flow will give you some direction...

see if you can get heat to come out the front vents rather then the floor...

f-bodyfreak

there are vent doors that change from outside air to heated air when you change it from hot to cold listen under the passenger side dash and you can hear them move and slam closed if you dont hear this the metal cable came off or the motor went bad also on some vehicles theres a valve in the heater core line that opens and closes with 12 volts or a cable