Would a blocked heater core cause a engine to heat up at idle

If the heater core hoses are hot but there is no heat coming out of the vents, and the vehicle is also overheating, there are several possible issues that could be causing this problem. Here are a few things to check:

1. Coolant level: Check the coolant level in the radiator and reservoir. If the level is low, it could cause both the overheating and lack of heat. Top up the coolant to the correct level and check for leaks.
2. Thermostat: If the thermostat is stuck closed, it could be preventing coolant from circulating through the engine and into the heater core. This could cause both the overheating and lack of heat. Consider replacing the thermostat if it is found to be faulty.
3. Water pump: The water pump circulates coolant through the engine and heater core. If the water pump is not working properly, it could be causing both the overheating and lack of heat. A mechanic can test the water pump to determine if it is functioning correctly.
4. Heater core blockage: If the heater core is clogged or blocked with debris, it can prevent hot air from circulating through the cabin. This could cause a lack of heat. Flushing the heater core may help remove any blockages.
5. Cooling system blockage: A blockage in the cooling system, such as a clogged radiator or hose, can prevent coolant from flowing properly and cause overheating. Have a mechanic inspect the cooling system to determine if a blockage is present.

These are just a few possible causes of the overheating and lack of heat. It is recommended to have a qualified mechanic inspect the vehicle to diagnose and repair the issue.

If both hoses are hot, the problem could be the inside...could be a blend door actuator

try some comma's?
my wild guess, is you are trying to fix a dead cab heater, right?
and if so, can be caused by 5 things wrong. total.
1 engine coolant not hot (180F or more)
2; fan dead.(cab heater fan)
3:or core , coolant path blocked. (seems you)
4; core exterior core blocked with leaves or pin needles. (sucked in)
5: optional core valve , stuck closed. (cable bad, etc)\



one pipe hot , means ,? core pipe 1 is hot, and other is dead cold?
this flow blockage , bingo !

if pipe 1 is 180F and other is 120f this is normal the heater is heating air in the cab and is dropping due to this heat exchange. (normal)
so why not do the 2 year full flush service now. (skipped i bet)
core hoses:
remove the 2 hoses on engine side, never core side (easy damage)
then back flush both hoses. with a garden hose.
if there is a valve there, test it and make sure it's opening... and free flowing.
and that both engine water ports are open too, from heater hose
to engine. (yes, they pack up too)

try to flush radiator,sounds like it has sediment in bottom of it

You may have a clogged heater core, thus restricting the flow of antifeeze in the engine, causing it to over heat. Are you certain that the car is over heating? Have you checked the coolant temperature switch? I would recommend that you run a system flush. To do this, you will need to turn the heater on while the flush is circulating. This will allow the flush to clean out the heater core.

No heat could be caused by a number of things, but first check the coolant and make sure that its full, next i would check the thermostat if its opening to soon its not allowing the engine to get hot most likely you would have a check engine light on with a code if this was the case being your car is post 96 and OBD2, another possible cause could be a blockage inside the heater core not allowing the hot coolant to cirrculate, if your coolant is dirty it may require a reverse flush of the entire cooling system to try and remove the dirt/rust.

a heater uses the temperature of the cars water, running threw a heat exchanger if the heater core has failed water will not circulate threw the engine properly this will and can cause over heating as well as nothing blowing from the heater. good luck.heater cores are generally inexpensive parts to replace.

last thing you can check if heater core is ok. is the thermostat.

Yes a heater core that is slightly plugged will do this.. Also I found once, that there is a restrictor inline in one of the heater hoses looked like a plastic hose connector and It had a large flake of lime that would intermittently block off flow check for this as well..good luck

Water-cooled engines supply heat for the passenger compartment by circulating hot coolant through a radiator-like heater core. The passenger compartment fan forces air through this heater core and into the passenger area. The flow of coolant for this purpose can be controlled with a valve in the line that is adjusted when the heat control is moved or via a flap that blocks or opens the air path through the heater core to adjust temperature.
The effect you describe can be caused by several different sources:
- A slipping belt which turns the water pump. - A partially collapsed hose in the circuit for the heater, causing a reduction of water flow to the heater core. - A heater core internally blocked from deposits from the water component of the coolant. - A valve which is not being adjusted through its normal range by the dashboard control. - A flap suffering the same limitation as above.
Another effect our personal vehicles generally show with age is caused by abnormally low engine friction attributable to a particular additive we use that reduces engine friction so much that the thermostat that controls coolant/engine temperature is wide open but the engine doesn't heat enough to bring the coolant temperature into the normal operating range. We notice on two of three vehicles, that rolling on a long downgrade (engine not loaded) will cause the engine temperature to drop below its customary operating temperature.
If you have a dashboard temperature gauge, watch it to see if it rises into the middle of the range or not. If not, there may not be much you can do other than flush the cooling system, making sure that the heater control is set to its highest temperature to ensure that the heater core is in the loop while flushing.

Sounds like you may have a partially plugged heater core. You could flush this out separately, from flushing radiator & engine block. Diconnect heater hoses going to your heater core and clamp off, so not to loose coolant from engine. Now hook up separate hose to one side of heater core pipe and flush out with typical garden hose. Repeat procedure on both heater core inlets. Reconnect original heater hoses and test difference. You may have to add an additional litre of antifreeze. If this don't work i suggest changing heater core. Good luck.........Ron.