Coolant from under dash
Thread Starter
6th Gear
Joined: Mar 2008
Posts: 6
Likes: 0
Coolant from under dash
Driving home from work last week, noticed temp gauge raising to about 260+. Thinking I blew a hose, I turned on the heater to relieve the temp and continued a few miles home. Suddenly, coolant began gushing from under the passenger side dash. 
However, the temp gauge began to lower and I was able to limp her home. Is this a heater core issue I've been reading about? How hard is it to repair, and can I do this in my garage?
Coolant leaked on the carpet (replacing anyway), but not from under the car. Any help and guidance will be appreciated.
She's a 73 coupe, auto, SB 350 w/ac., driving, resto-in-progress.
However, the temp gauge began to lower and I was able to limp her home. Is this a heater core issue I've been reading about? How hard is it to repair, and can I do this in my garage?Coolant leaked on the carpet (replacing anyway), but not from under the car. Any help and guidance will be appreciated.
She's a 73 coupe, auto, SB 350 w/ac., driving, resto-in-progress.
Team Owner
Joined: Jul 2008
Posts: 23,419
Likes: 22
From: In limbo
St. Jude Donor '13-'15, '17 thru '22
Since you have an A/C car, there is supposed to be a cut-off of coolant to the heater core when the heat is not on to prevent the heat and A/C from fighting each other. If I had to make a guess, I would say that you have a leak in your heater core, that didn't show itself until you turned on the heat. If your cut-off is working properly, you can probably engage the A/C to cut off the flow to the core and leave it that way until you are ready to address it. I have never changed the heater core in one of these cars, so I will leave that to the better informed. I probably wouldn't dive into changing the core until I was confident that all the hoses and connections to and from it were tight.
However, the probable leak in the heater core is almost certainly not what caused your initial overtemperature problem. The common first suspect, a thermostat that broke and went closed, is probably not at fault here because if that happened you wouldn't have seen the temperature drop when you turned on the heat. I also wouldn't suspect a water pump for the same reason. If I had to guess, given the little information provided, I would say fan, fan clutch, or a blockage of the air over the radiator or in the radiator.
However, the probable leak in the heater core is almost certainly not what caused your initial overtemperature problem. The common first suspect, a thermostat that broke and went closed, is probably not at fault here because if that happened you wouldn't have seen the temperature drop when you turned on the heat. I also wouldn't suspect a water pump for the same reason. If I had to guess, given the little information provided, I would say fan, fan clutch, or a blockage of the air over the radiator or in the radiator.
Le Mans Master
Joined: Oct 2005
Posts: 6,247
Likes: 471
From: Glen Allen, VA
I hate to say it, but that sounds like classic heater core leaking to me. I too have never replaced one in these cars, and I'm not sure I want to. In the vehicles I have done on in, it wasnt' bad at all. C3's apparently are not easy.
Melting Slicks
Joined: Aug 2002
Posts: 3,334
Likes: 4
From: Midland TX
I'm not sure if the 73 has the shutoff PKguitar mentioned. I know they did not put it on the 72.
You will need to remove the a/c evaporator housing (the big box mounted on the firewall in the engine compartment), the passenger side dash, and the ductwork behind the dash. Do you have an Assembly Manual. There are a few screws that are hard to see.
While you have the evaporator housing off, it is a good time to clean out the debris. I found all kinds of leaves and crap in mine.
Fortunately I had my engine out when I replaced mine. I have a 454 so space is very limited in the engine compartment.
Good luck. This has to be one of the worst repairs.
You will need to remove the a/c evaporator housing (the big box mounted on the firewall in the engine compartment), the passenger side dash, and the ductwork behind the dash. Do you have an Assembly Manual. There are a few screws that are hard to see.
While you have the evaporator housing off, it is a good time to clean out the debris. I found all kinds of leaves and crap in mine.
Fortunately I had my engine out when I replaced mine. I have a 454 so space is very limited in the engine compartment.
Good luck. This has to be one of the worst repairs.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 98
From: Ontario
Yes you can do it in your garage. But it does take a lot of time. And there are a few tricks. Mine took 12 hours but I was an amateur never having done that job before.
This is the stud and nut on the firewall side. People keep tugging and tugging on the passenger interior and can't figure out why the unit shown above won't move. This why.
This is the stud and nut on the firewall side. People keep tugging and tugging on the passenger interior and can't figure out why the unit shown above won't move. This why.
Last edited by Paul L; May 18, 2009 at 04:05 PM.
Thread Starter
6th Gear
Joined: Mar 2008
Posts: 6
Likes: 0
I was afraid of this. Welcome to the restoration world! At least this will be the biggest task yet. It will give me a chance to remove and repaint plastic parts, clean gauge clusters, and repair any subsequent "bubba" rigging.
I will do this only once. I have a manual and will draft a buddy for a second set of hands. I have read this is a PITA, and I truly appreciate the quick response from my fellow 'vette friends!
More to come.
I will do this only once. I have a manual and will draft a buddy for a second set of hands. I have read this is a PITA, and I truly appreciate the quick response from my fellow 'vette friends!
More to come.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 98
From: Ontario
I was afraid of this. Welcome to the restoration world! At least this will be the biggest task yet. It will give me a chance to remove and repaint plastic parts, clean gauge clusters, and repair any subsequent "bubba" rigging.
I will do this only once. I have a manual and will draft a buddy for a second set of hands. I have read this is a PITA, and I truly appreciate the quick response from my fellow 'vette friends!
More to come.
I will do this only once. I have a manual and will draft a buddy for a second set of hands. I have read this is a PITA, and I truly appreciate the quick response from my fellow 'vette friends!
More to come.
So I sucked up my pride and went home. Then did the job in the garage. No regrets; not a fun experience but a learning one. And if people have seen my other threads on stereos, there was the opportunity to replace the head unit, upper dash speakers, etc.
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Racer
Joined: May 2008
Posts: 353
Likes: 0
From: boulogne buenos aires
I had the same issue...leaking heater core.. I by passed the hose so no water in the core.. anyway In this cars and my climate the heater is not required....I´d kill for an a/c I suffer in summer!!!
Drifting
Joined: Nov 2002
Posts: 1,951
Likes: 1
From: Shore NJ
The 73 with A/C did come with a inline heater block off valve vacuum operated by the little black vacuum line from the dash. If you look under my past posts I went into detail how to change the heater core. I can tell you that it's not a hard job, just time consuming and alot of stuff to remove and reinstall. The hardest thing you have to get to is the screw that holds the bracket that holds the hoses to the heater core, also remove the passenger side of the dash, all of the A/C ducts, center dash, heater box, and more. I actually did this while I had the engine out which helped with room. I can recommend also after all of the work to remove the old core make sure you pressure test the new core for leaks before you install it!....good luck
Also: while everything is apart make sure to vacuum test the actuators/two of them for the vents while there out before you reinstall everything including the new seals/kit you will need......
Also: while everything is apart make sure to vacuum test the actuators/two of them for the vents while there out before you reinstall everything including the new seals/kit you will need......
Last edited by 73jst4fun; May 19, 2009 at 03:59 PM.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
All good advise above, I will add 1 thing, when your temp is high and you spring a coolant leak it is alarming for the temp to drop. The temp sender needs to be submerged in coolant to read correctly, if the coolant were to all come out suddenly, the temp gauge probably wouldn't show extreme overheat before the engine was cooked. Just an observation from the line of work I'm in.
Le Mans Master
Joined: Oct 2005
Posts: 6,247
Likes: 471
From: Glen Allen, VA
One more suggestion. After you purchase the replacement heater core, take it to a shop and have it leak tested before installation. This job is enough of a bear that you don't want to have to go back in and replace a heater core that has a factory defect.
Thread Starter
6th Gear
Joined: Mar 2008
Posts: 6
Likes: 0
Thanks for all the feedback! I'm still putting together my parts order-checklist for this repair. I'm taking my time with this because I certainly don't need to go through this again.
I'm still perplexed on why the temp gauge lowered while getting her home. Fortunately, I didn't drive far to get home, so I hope that the high temp didn't cook any parts; thanks for the advice aktbird. I had to move the car a couple of days ago, and she started fine with no adverse noises. We'll just have to wait and see after this repair.
Thanks again for all the photos too, Paul 74. I'll know what to look for.
I'm still perplexed on why the temp gauge lowered while getting her home. Fortunately, I didn't drive far to get home, so I hope that the high temp didn't cook any parts; thanks for the advice aktbird. I had to move the car a couple of days ago, and she started fine with no adverse noises. We'll just have to wait and see after this repair.
Thanks again for all the photos too, Paul 74. I'll know what to look for.
Burning Brakes
Joined: Jun 2008
Posts: 1,086
Likes: 1
From: Michigan
The 73 with A/C did come with a inline heater block off valve vacuum operated by the little black vacuum line from the dash. If you look under my past posts I went into detail how to change the heater core. I can tell you that it's not a hard job, just time consuming and alot of stuff to remove and reinstall. The hardest thing you have to get to is the screw that holds the bracket that holds the hoses to the heater core, also remove the passenger side of the dash, all of the A/C ducts, center dash, heater box, and more. I actually did this while I had the engine out which helped with room. I can recommend also after all of the work to remove the old core make sure you pressure test the new core for leaks before you install it!....good luck
Also: while everything is apart make sure to vacuum test the actuators/two of them for the vents while there out before you reinstall everything including the new seals/kit you will need......
Also: while everything is apart make sure to vacuum test the actuators/two of them for the vents while there out before you reinstall everything including the new seals/kit you will need......