Heater issues with my truck

ellwoodjake

Old Mossy Horns
Since this recent arctic weather, my heater is blowing nothing but cold air. It is an older Chevy with the 350 vortec. My temp gauge is showing normal, like it always has, and takes the same time to get there. Heater and radiator hoses feel hot to the touch and the level on the coolant tank is full when hot. I braved the elements and put in a thermostat, to no avail. Coupla days ago, I went on a 40 mile trip(wearing a coat) and while I was there, a cousin of mine squeezed the top radiator hose "I saw this done somewhere", and after about 5 minutes of pumping, the heater blew hot, and I was able to get home without a coat. Next day, same thing, cold air, WTH. Anybody got any ideas?
 
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hunthard2

Twelve Pointer
Contributor
Buildup limiting coolant getting to the heater core? When you say pumping, that was your cousin pumping or you mean it ran for 5 minutes? If the former I’d be looking at the water pump
 

ellwoodjake

Old Mossy Horns
hunthard2 said:
Buildup limiting coolant getting to the heater core? When you say pumping, that was your cousin pumping or you mean it ran for 5 minutes? If the former I’d be looking at the water pump
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My cousin was pumping the hose like he was giving it CPR. :LOL:. After it starting blowing hot, I immedately headed out, never shut it off, 'til I got home. That heat all the way home, felt GREAT!
 
bigten

bigten

Old Mossy Horns
Contributor
Run engine to operating temperature, them feel BOTH heater hoses. Both should be the same temperature. I'm thinking you will find one that is significantly cooler than the other. That could be caused by a couple or so things, one being a restricted core, a malfunctioning heater control valve or a low coolant level. Just because your overflow tank is full doesn't necessarily mean the engine is fully topped off. A bad radiator cap can keep coolant from returning from the tank to the radiator. I would assume by "pumping" the radiator hose, that simply temporarily purged air and forced coolant circulation. Oh, prior to starting engine, remove radiator cap and visually check coolant level. Radiator should be completely full. If it isn't, top it off and replace cap with a new one, then run above tests.
 

hog&deerhunter

Ten Pointer
I have a Lisle coolant filler. The design is really nice in that it will purge air from the system while filling the radiator and no spill. I bought mine on Amazon. They have adapters fir different vehicles. Here is the one for GM, but double check it. I really like it.

Use it while the engine is running.


Lisle Funnel
Lisle Funnel https://a.co/d/ahBiUnZ
 
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Sharps40

Sharps40

Old Mossy Horns
If your truck is a closed system (pressure vent cap on recovery tank, not radiator) check for low coolant as follows. E.g. at any other time you will likely see coolant in the tank.


Engine cold overnight, fluid of any quantity, visible in tank

Watch the tank.

Helper starts engine.

If tank then runs empty (even if it later shows fluid) your system is low at least a quart and this is your no heat issue.

When engine cools again, top off the overflow reservoir and restart checking to see that the initial start up does not drain the reservoir. Repeat cold until reservoir maintains a level of coolant at that initial cold start rush.
 
“J”

“J”

Twelve Pointer
bigten said:
Run engine to operating temperature, them feel BOTH heater hoses. Both should be the same temperature. I'm thinking you will find one that is significantly cooler than the other. That could be caused by a couple or so things, one being a restricted core, a malfunctioning heater control valve or a low coolant level. Just because your overflow tank is full doesn't necessarily mean the engine is fully topped off. A bad radiator cap can keep coolant from returning from the tank to the radiator. I would assume by "pumping" the radiator hose, that simply temporarily purged air and forced coolant circulation. Oh, prior to starting engine, remove radiator cap and visually check coolant level. Radiator should be completely full. If it isn't, top it off and replace cap with a new one, then run above tests.
Click to expand...
Is the heater control valve, electronic or manual (cable) operated?
 

ellwoodjake

Old Mossy Horns
Sharps40 said:
If your truck is a closed system (pressure vent cap on recovery tank, not radiator) check for low coolant as follows. E.g. at any other time you will likely see coolant in the tank.


Engine cold overnight, fluid of any quantity, visible in tank

Watch the tank.

Helper starts engine.

If tank then runs empty (even if it later shows fluid) your system is low at least a quart and this is your no heat issue.

When engine cools again, top off the overflow reservoir and restart checking to see that the initial start up does not drain the reservoir. Repeat cold until reservoir maintains a level of coolant at that initial cold start rush.
Click to expand...
Did this before and after changing the thermostat. Also removed the coolant tank cap (no radiator cap) to make sure there was no vacuum. replaced cap after starting engine.
 
np307

np307

Ten Pointer
If the heater hoses are warm, I'd bet it's a blend door problem.

Edit: I just read again and if he was able to get it to blow hot by squeezing the hoses you either have a clog in the heater core or air trapped in the system.
 
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ellwoodjake

Old Mossy Horns
Took my heater hoses loose today, and was able to blow through them by mouth, both directions. I have an old waterhose in the basement right now getting warm and pliable. Tommorow, I plan to park my old haytruck beside the Chevy and see if I can heat things up with the haytruck engine and the waterhoses. The haytruck heater core was bypassed years ago, so this should be a quick and easy check.
 

ellwoodjake

Old Mossy Horns
Well, got a chance to pull the old farm truck alongside the Chevy, and run a couple of water hoses between them. As soon as I got the engine warmed up, and turned the Chevy fan on, yep, you guessed it. Plenty of heat in the Chevy. Looks like I've ruled out heater core, heater hoses, heater fan, and blend doors. Now I'm really stumped. Could it be the water pump putting out just enough pressure to cool the engine, but not enough to push through the heater? The thing cooled just fine over the summer, even when pulling a trailer. In all my years, I've never changed a waterpump, unless it was leaking, overheating, or the shaft was moving. On the way home, tomorrow, I plan on stopping at the parts store and grabbing a new cap for my coolant tank. I have no idea what my system pressure is, maybe a little more pressure will help prime my pump 🤷‍♂️. Hell, who knows, right now, I'm just grasping at straws.
 
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“J”

“J”

Twelve Pointer
ellwoodjake said:
Well, got a chance to pull the old farm truck alongside the Chevy, and run a couple of water hoses between them. As soon as I got the engine warmed up, and turned the Chevy fan on, yep, you guessed it. Plenty of heat in the Chevy. Looks like I've ruled out heater core, heater hoses, heater fan, and blend doors. Now I'm really stumped. Could it be the water pump putting out just enough pressure to cool the engine, but not enough to push through the heater? The thing cooled just fine over the summer, even when pulling a trailer. In all my years, I've never changed a waterpump, unless it was leaking, overheating, or the shaft was moving. On the way home, tomorrow, I plan on stopping at the parts store and grabbing a new cap for my coolant tank. I have no idea what my system pressure is, maybe a little more pressure will help prime my pump 🤷‍♂️. Hell, who knows, right now, I'm just grasping at straws.
Click to expand...
Be careful with getting a cap that allows too much pressure. You can damage the radiator in the process. Especially if the radiator is original.
 

ellwoodjake

Old Mossy Horns
“J” said:
Be careful with getting a cap that allows too much pressure. You can damage the radiator in the process. Especially if the radiator is original.
Click to expand...
I don't worry about radiators, they're easy to change, but heater cores......... :ROFLMAO::ROFLMAO: I bought a factory replacement cap, but hadn't got a chance to put it on yet. Didn't see any pressure ratings written anywhere on it, but I assume it's around 15-20 lbs. This is why I was a little reluctant to flush the heater core, and just blew it by mouth. My water hose at the basement puts out around 60 psi. Great for washing cars, but can be hard on heater cores and radiators. I believe this is why my haytruck heater is bypassed now.:rolleyes:
 
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