Thanks for looking...

Fall is coming and I went to use the heat on our convertible - got nothing but cold air. It worked fine last year. I went though the Troubleshooting suggestions in the 1967 FSM and found nothing wrong: Blower works, the water flowing to/from the core feels hot on the hoses, the damper that directs the hot air seems to work, the airbox damper arm moves properly, the control cable is intact.

What would you check if you had no heat from your heater?

Can a heater core get clogged? My radiator fluid isn't ugly or anything..

I'm a little stumped. I think I'll just keep checking the FSM and everything again, I think I tried all the modes; floor heat vs defrost, but I'll keep checking..

Looking for any and all ideas. ....Drill some holes in the firewall..?

Thank you,
- Art

Sounds like a plugged/restricted core.

OK. I'll let it get cold and when I start it next time check if the supply/return hoses get hot or if they stay cool, or what's what.

Thx. - Art

If you have an infrared temp gun, check for a 15-20F drop from the inlet-> outlet temps. You can also use that to check the heater box to see if it's heating up. Make sure there isn't a shut off valve under the dash, they can stick closed and cause the same issue. HTH, Steve

When I was stationed in San Diego I had a 72 Swinger, one rare day it got cold enough to need a heater. No heat. usually that means you are low on coolant, but not in my case (did you check yours?). Turns out the core was plugged.

All I did was disconnect the heater hoses and use a garden hose to flush one way till the water ran clear, then the other way till it ran clear. Took a couple of times going back and forth till it ran clear both ways from the get go. Plenty of heat after that.

Guys, thanks so much,
Those are excellent ideas to try - I've got an infrared temp gun and I'll see what it tells me, shut-off valve isn't mentioned in the FSM, but I'll look closely at all the plumbing - and I'll go ahead with the flush too in the morning.
- Art

If you have a heater only there is no shut off valve. Only a hot cold blend door in the heater box.

Thanks, .. yes this is what my FSM shows, and AFAIK the blend door works cuz the lever arm moves freely and I can hear the door inside sort of slam against its stops when I operate the cold/hot selector lever.. and it's a very original car ...but ya never know if a PO could have rigged something weird, I'll check for it anyway..

I had an old chevy when I was young that we all thought was just cold blooded and had a poor heater. Tried the 1970's fix of cardboard in front of radiator and it still sucked.

Finally one day I decided to flush the core out with a garden hose. Took both hoses of engine an just hit it with moderate pressure every so often till it flowed freely. And what do you know I ended up with a heater that would melt snow of the car.

There isn't a heater control valve on this? Only later model cars had a HCV (water)?

66-70 B-body Heater control valve only with factory A/C system. Standard heat has no heater vavle in the supply line.

Whatever is wrong must be pretty simple or basic. There are so few moving parts to this setup.

Got to spend a little time on this today:

- Checked coolant and it looks very clean, no crud.
- At engine start the water pump housing rose to 125F within 5-10 minutes, but both supply and return hoses from the water pump remained at 80F. I started wondering if I could have a blocked hose, or blocked nipple at the water pump - then I noticed there was a rattle sound from the water pump, so maybe an impeller problem?
- Took it for a drive and got it up to temperature: Forgot to try it in Defrost mode, but switching from Heat to Cold I got no change in air temperature.
- The blower motor works, and I get decent airflow out of the air outlet pointed at my feet.
- Back at the garage, I kept engine running at idle and measured 185-188F at the water pump housing. At the firewall, the driver's side hose measured 156F (inlet), the passenger side hose measured 114F(outlet) - so there must be flow thru the core. I forgot to notice if I still had the rattle sound from the water pump.

This seems like a functional core, but there is no harm flushing it, plus the hoses and nipples tomorrow. Maybe airflow thru the core is the problem, like the fins are clogged with lint or something, but that's internal to the airbox, so last ditch effort only.

I'll keep looking and fiddling with it.
- Art

Just flush the core and be done with it. You are most likely reading heat conducted back from the engine thru the coolant to the output side of the heater core. 114 degrees is nothing really, especially since you are getting no heat removal thru the heater, were did the 40 degree difference go?

1.) Thx. Will do.

2.) I have no @^#% idea. Agree, 40F is a big diff. It's not coming into the cabin. There is normally always hot coolant flow thru the core though, because there is no hot-coolant-shut-off-valve in the plumbing, only a damper/door that directs airflow from the core.

Thanks, I'll get into it after I get the NYS Inspection done today.
- Art

Don't be surprised if the nipples on the block are partially clogged. Just clean them out and you're good to go.

Yeah, I was thinking this is possible with corrosion at the metal nipples, the water pump and t'stat housings are already kinda cruddy... if the crap gets dislodged and then caught in the core.. and it won't show up in the radiator cuz it's all stuck in the core..

..today I'm waiting for my local gas station to finish a State Safety Inspection on it before I get further into this..

Cheers, - Art

I also had a 60's Mop with no heat. I flushed the core at the nipples of the core- and filled the interior with water.
Pull the hoses at the water pump as suggested above to prevent the same screwup I had.
On the plus side the heater worked great afterward.

Flushed the heater core and got heat.

Took 15 minutes. Tapped a gallon or so of coolant from the radiator spigot. Unclamped the coolant hoses at the firewall nipples and flushed garden hose water thru backwards (flush water went in the passenger side nipple). Some milky crud came out but not much. Ran water til it all came out clear.

Then I decided to flush the whole system, removed the radiator cap and ran hose water thru the same heater hoses to the water pump and let it clear out. Refilled w glycol.

...no water on my carpet..





Thanks all.
- Art

Glad it was easy and you posted the results!