[al1950]

my 66 Grand Prix w/ac start leaking heater core today. can I disconnect the heater hoses from the core and connect them together temporary fix till I can replace core? thanks Allan
also does any one know the over process of how the core comes our, it is not covered in my chassis manual.

[grivera]

I can’t help you with the removal but you can certainly bypass the heater core - just get yourself a 3/4 to 5/8 adapter

[Joe-Touring]

I82much, one thing you can do, if you ever take the heater box out, is to clean the old foam off the air blend door(this door moves when you adjust the heat slider) and replace with new foam. This helps the door seal better when your HVAC control is at full cold.

I will say that it’s not a very fun job since you have to take the fenderwell out and a bunch of butyl ribbon seal on both sides of the the firewall.

[zippy]

I have a shutoff in the inlet to the heater core on my TA And I notice a little cooler engine temps in the heat of the summer for sure. No hot coolant just bypassing back into the pump.

[grivera]

Are you saying it runs cooler when you shut off flow to the heater core?

[steve25]

I have seen this same thing, reason being pump pressure is being reduced on one bank of the motor to feed the core.

[HWYSTR455]

PSI in the heater core is the same as the rest of the system on the engine side of the t-stat.


.

[HWYSTR455]

Let me rephrase, PSI will not exceed the PSI of the system on the engine side of the T-stat.

Flow is only restricted at times, if it has a cutoff valve.



.

[zippy]

Originally Posted by grivera

Are you saying it runs cooler when you shut off flow to the heater core?

Yup, I noticed a few deg cooler. 7-10 maybe. And my elec fans take longer to cycle in stop and go traffic

[zippy]

Originally Posted by steve25

I have seen this same thing, reason being pump pressure is being reduced on one bank of the motor to feed the core.

Pressure isn't being reduced, it's static throughout the whole system. But flow is greater in the pass head when running through the heater core. BUT, if not extracting any heat in the heater core, then the hot coolant just recirc's back to the pump inlet. Thus actually heating up, the incoming coolant from the radiator.
Hotter inlet coolant temp, will require hotter outlet coolant temp to open T stat more and flow more through the rad to counter act the heater core line heating.

[69Customs]

I ran into this same problem of floor heat in convertible. So I checked into it. In 1969 gm did not put a vac operated heater valve on NON AC cars. Only cars with ac got a heater vacuum valve.
The standard non ac heater control works with mechanical cables only. The ac/heater control has vacuum controls which controls a vacuum heater valve.
I found my heat problem to be the blend door was not all the way closed with the mechanical cable. There is an adjustment on the cable at the heater box. Mine was not adjusted properly. After I followed the manual and adjusted it, the heat was cut out. I did also put in a 2005 heater valve that I modified from vac to cable control with the cable under the dash. That way on cool late summer/fall nights I could leave the top down and still control water thru the heater turning it off or on. I did find out that the 2005 gto heater bypass valve doesn't shut heater flow off completely but diverts like 90% around heater core.
I do expect to hook the cable on the heater control box arm that controls the heat so it also turns the bypass valve on and off.

[Cardo]

I have 2 1965 factory air cars. No heater water vacuum control valve was on either one. I did install one like J Schmitz shows, and it made no difference but did leak intermittently. I took it out when I was doing some other work in that area. Consistent 34-35 degree air from A/C ducts both with and without the valve on a r134a charge.

[zippy]

This is how I block my heater core. A cheap hose crimp tool for mechanics. Avail at most auto tool places.