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Discussion Starter #1
So I just redid the water pump, timing cover and chain, radiator, belt system and all hoses etc etc on my '66 (400/400).

It is running great with no visible leaks. BUT, once up to temp (160ish) I'm getting a faint coolant smell and some "steam/smoke" coming in through the dash vents, which is warm and fogs up the windshield. My heater blower has not worked for a decade and the car sat for several years prior to this refresh. Are these signs of a bad heater core? Could a leak that I am missing be dripping onto the headers or something to create this? I cannot for the life of me see any coolant leaks, or any fluid leaks, while the car is idling. Tempted to just bypass the core and plug the ends, but eager to hear any ideas of what else it could be.

Also having some significant what seems like blow by exhaust. Not coming from the valve cover breathers and my PCV is hooked up right. Similarly, no easy to see exhaust leaks or manifold issues. Perhaps related? I swear something is dripping onto the headers but I cannot tell what!!!!

I know a "diagnosis" is impossible with this description, just hunting for ideas what top check next. Thanks!
 

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Make sure your hoses are tight at the core so it don't dribble inside. If the leak continues.... time to change the core. Mine was fine before my engine rebuild, once I got it running again the core was leaking.
 

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Yeah, bypass the core and see if that solves the problem. If it does, then you know what the problem is.

Bear
 

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Discussion Starter #4
Thanks both.
I get that if I could see a coolant leak under the dash, or at the firewall, or at any hose ends it would likely be the core, but no leaks at either spot. just smoke/steam coming from the dash vents, which I've never heard of as a heater core failure symptom.

I was actually going to bypass the core anyhow, since my heater control springs broke years ago and the car is in CA...now another reason to do it. But the smoke is weird...
 

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Thanks both.
I get that if I could see a coolant leak under the dash, or at the firewall, or at any hose ends it would likely be the core, but no leaks at either spot. just smoke/steam coming from the dash vents, which I've never heard of as a heater core failure symptom.

I was actually going to bypass the core anyhow, since my heater control springs broke years ago and the car is in CA...now another reason to do it. But the smoke is weird...
May just be condesation. Have had the same expereince, not the heater core. I believe this is why so many dash panels rot out near the windshield on the 1968 and up bodies. I don't know if water gets into the system from a bad seal or what, but it does happen. Installing a new heater core can't hurt seeing its age and you can re-seal things if there are seals that need it.
 

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Discussion Starter #8
well, just checked car and there is a nice pool of coolant in passenger footwell. dripping through the floorboard right next to header/exhaust junction.

I'll be bypassing the heater core ASAP.

Any good method to getting all the residual coolant out of it, or just wait for it to drain into my interior:sneaky:? once bypassed leave inlets open or cap?

thanks!! glad this is solved.
 

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Ylw , once years ago I had coolant “green smoke -hot vapor”
Start pouring out all windshield dash vents while also dumping on the floor while going down a 6 lane freeway at 7am and it wouldn’t shut off at all , within seconds I could not see the road as all windows were fully fogged up with anti-freeze I and was surrounded by Other cars all going 65mph, it was a panic scene trying to drive off the freeway with my driver window the only way to see out even the rolled up passenger window was useless. I made it but a wake-up call I never forgot

If you had a way to get some low air pressure into one side of the core thru One of its hose lines it could push what’s left of the water all out the other side..

Like mounting a tire stem valve on a cap
Screwed on a 1/2” piece of pipe Abs or steel and clamping it onto one core hose with a hose clamp , add low air pressure to the stem valve , if leaks not very severe the cores would empty , then rubber cap off both ports ,
Yanking out a heater core is usually a PITA
Otherwise it might take a long time to drain on your rug if you don’t
 

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Discussion Starter #10
Ylw , once years ago I had coolant “green smoke -hot vapor”
Start pouring out all windshield dash vents while also dumping on the floor while going down a 6 lane freeway at 7am and it wouldn’t shut off at all , within seconds I could not see the road as all windows were fully fogged up with anti-freeze I and was surrounded by Other cars all going 65mph, it was a panic scene trying to drive off the freeway with my driver window the only way to see out even the rolled up passenger window was useless. I made it but a wake-up call I never forgot

If you had a way to get some low air pressure into one side of the core thru One of its hose lines it could push what’s left of the water all out the other side..

Like mounting a tire stem valve on a cap
Screwed on a 1/2” piece of pipe Abs or steel and clamping it onto one core hose with a hose clamp , add low air pressure to the stem valve , if leaks not very severe the cores would empty , then rubber cap off both ports ,
Yanking out a heater core is usually a PITA
Otherwise it might take a long time to drain on your rug if you don’t

That sounds gnarly!
I had a similar experience with an 80 Dodge panel van hood flipping up on me at hwy speed going over the Hwy 17 pass in Santa Cruz. Whole windshield blocked, terrifying experience. The latch failed, sold that POS the next day!

Thanks for the tips, gonne do this next week.
 

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You are very fortunate you acted when you did. Many years ago I noticed a wisp of steam come out of the dash vent and ignored it thinking (hoping) it could be condensation. A few days later I saw a drop of antifreeze on my passenger floor mat. No garage, brutally cold time in NY winter; I chose to ignore it and change the heater core when things warmed up. Bad idea. Things heated up very quickly to my chagrin. Took a friend out for a ride and immediately after speed shifting second gear my heater core let go. Steam came out of the dash vents and hot antifreeze flowed into my console, ruined several of my 8 track tapes. As I said, it was many years ago.
 

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Discussion Starter #12
Got the heater core bypassed. no more leaks, no more smoke.

I blew the residual coolant out of the core with extra hose and lung power.

now to dry the carpets...
 
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