I think my heater core is clogged

[jct]

Out driving my car on the highway with the heat somewhat pumping away not exactly hot but warm enough than all of a sudden it's blowing cold in my face. I haven't touched the temperature setting all summer due to the rubber valve that i don't want to fail ('68 Chrysler) my only conclusion is it's clogged, i don't smell any coolant and not leaking anything

My temp gauge shows a rock solid 180°F and i have a Robert Shaw 180°F thermostat

Hopefull the heater core needs is a reverse flush

 

[Mr C]

Need more info...is it Autotemp? What setting was it on? Vent? Defrost?
What was the outside temperature differential?

Once I panicked because the air stopped flowing through the vents one morning. Turns out my autotemp sensed the outside temp was what I wanted the inside temp to be, so it stopped the fan because it achieved what I asked of it.
Once it got warmer, click! The fan came on again to cool the interior.

 

[jct]

Just the standard a/c car with no autotemp

Ranco water valve

I've had the setting on full heat all the time, it was on the defrost setting, no change when i moved to heat setting

Temperature outside was in the upper 40s

 

[LocuMob]

Coolant level check out?

 

[stubs300]

I had a 66 Rambler American that the heater went out on the Divide in Wyoming in some shitty weather when I really needed it most. I had to suffer the next 3 days till I got to Rapid City where after doing a thorough flush and back flush and flush again that I had heat. Good Luck

 

[jct]

Haven't checked the fluids yet ran out of day light and it was at temp. Probably be able to get to it this coming weekend

 

[david hill]

The loss of a few quarts of coolant can result in loss of coolant circulation. If the cooling system is full check to see if both heater hoses are hot when warmed up. If the core is plugged there are flushes out there to help you.

 

[jct]

Added a some antifreeze, i could still see it at the top of the radiator with about 1.5" or so air gap, ran the car heater works fine, played with the heater control a two or 4 times still operational not leaking, idk why it was blowing cold air in my face
¯\_(ツ)_/¯

 

[david hill]

Good to hear it was only caused by low coolant. Inspect the rad. cap and pressurized the cooling system w/ cold and fully warmed up to start. Look inside the valve cover vent for slug w/ a reddish gray tint to it. If found coolant may be leak onside the engine. Keep me posted w/ what you find.

 

[jct]

Shouldn't be the head gaskets i i replaced those when i rebuilt the top end used metal head gaskets

I'm using a 180°F Robertshaw thermostat

Gonna keep playing with my engine timing some more

 

[jct]

If i keep it under 70mph I get tons of heat via the heater core, 75mph and above for around 30+/- minutes or longer heat goes away get off the highway from that speed still no heat, felt the heater hose return line, it was cool to the touch, supply line has plenty of heat, wonder what is causing it to gunk up at those speeds? I still think I'll need to flush out the heater core. Which i should have done when i had the the heater control valve out/top end of my engine apart/timing chain. Never thought of doing that, at that time... :-|

 

[david hill]

It sounds like your heater core is plugged again w/ rust and crud from the engine and maybe the radiator. Flush the heater core as you did before. Bypass the core with a long length of hose to promote circulation and flush the engine separately till the coolant drains clean. Removal of the engine block drains will be required. If the drains are plugged fashion clean out tool / a coat hanger. Rigorously us the coat hanger to help break up scale in the block. When done refill w/ fresh antifreeze. Give this a try and heater core plugging should be over.