[gearbanger]

I disagree that it won't have any effect on the cooling. But I think it has a positive effect. The heater circuit allows water to be circulated through the engine and back to the heater without ever circulating through the radiator. So you constantly have part of your water not going through the radiator. If the heat is not switched on and the blower not running as is always the case in the heat of the summer, you will not be giving up any heat at the core so, by not circulating all the water in the radiator you are losing cooling capacity. I think blocking the heater circuit, not just connecting the lines together like I have seen some do, will actually make the engine run a little cooler. I may not make a dtectable difference on the guage but I think if there is any change it would be to the cooler side.

[engineer]

"IF YOU HAVE HEAT COMING INTO YOUR INTERIOR ALL THE TIME YOUR A/C WOULD HAVE TO WORK EXTRA HARD,EVEN MORE ON HOT DAYS." no one said that there was heat into the interior of the car, what was described correctly is the diverter air door has a built-in stop to prevent the door from totally closing off the air flow on a 67 gto with factory air. That air goes back to the blower motor through the factory air hose directly into the motor.
"Funny, I don't have heat coming into my interior all the time. Wouldn't that be an asinine way for Pontiac to design an air conditioning system?" There is no heat going into the car. By the way, GM and Pontiac always had water and air flow thru the heater boxes with factory air system. This keeps mold and condensation from building on the heater core when the AC system is on. "My door does close all the way ...Possibly it is time to fix your door" If your door closes all the way on the kick panel end of the AC heater box then the stop is missing and it is not working properly. "If the heat is not switched on and the blower not running as is always the case in the heat of the summer, you will not be giving up any heat at the core so, by not circulating all the water in the radiator you are losing cooling capacity" Did you notice that from 1967-1972 all the GM blowers usually ran on low speed in any heater position including off. There was no off switch position for the blower motor itself. "I think blocking the heater circuit, not just connecting the lines together like I have seen some do, will actually make the engine run a little cooler." I totally agree that blocking off the heater is the only way to do it, not connecting the lines together.

[lust4speed]

From the 1967 Pontiac Service Manual: "With OFF sector exposed in panel window, no air flow or motor output will result".

Later cars did keep the fan on all the time - but not 67's. OFF was truly off. The little hose you are referring to connects the back of the motor to the air inlet duct to keep the fan motor cooled with relatively clean air, and has nothing to do with the heater core, and does nothing when the fan motor is not running.

If Pontiac meant to leave the heater door open a bit, then they should have saved the money they wasted on the foam seal around the door edge. And they also should not have shown the diagram with the doors going all the way shut in my service manual.

[skip65]

if your door is open there is heat coming into the car if you have water flowing through heater core.original question.
Is bypassing the heater core to the rear of intake going to comprimise the motor from cooling properly answer no waterpump will circulate water from back of the head into the suction or return side of pump until thermostat opens, all water flows through rad as t-stat opens and closes.it follows the same path except it goes through heater core if it is hooked up.if you box is closed you get very little heat inside car,if box is open you cant help but get heat inside.the heater core is a luxury it was not meant to help in cooling engine.

[rudytadow]

Greeings,
Last fall, after having finished the coolant bypass, (heater core sprung a leak) on my 65 LeMans (326 V8) it is set up for air but its disconnected. I replaced the hoses,water pump, thermostat,I drove for about 30 minutes. It ran sluggish and the temp gauge was between 190 and 200. When I get her out of storage in about a month, I would like to get to the heater core. Does anyone have pics of removing their fender and dash exposing the heater core? I understand I'm in for a real treat. Any pics or suggestions?
Thanks.
Rudy

[wheelspin]

Rudy,

Your factory service manual describes this in detail complete with exploded views. The dash is not removed as the heater box containing the core resides under the dash bolted to the firewall. Additionally, the fenderwell is removed for underhood access, not the fender.

Les

[gearbanger]

I don't know about an air car but I changed my heater core in about an hour on my non-air 67. You have to take the nuts off the heater box from under the hood and remove the lines, then it comes right out from under the dash. Swap the core and pop it back on. Helps to have a buddy hold the box untill you get a nut on.

[SupergasDil]

Hi Ragtop, where can I get those nipples and what do I ask for?

[rudytadow]

A Good Morning to all!
After having read responses thus far,
I didn't see a concesus (yes or no) to my original question. The overheating (220F) that I saw while driving the car to storage in the fall, would it have been caused by the bypass? To recap, my 65 LeMans 326 2 spd auto with air (not connected) 2 weeks prior to storage, I flushed the coolant system, trashed my heater core, cleaned the passenger side floor of coolant - for 3 days, replaced the water pump, all hoses, coolant, radiator cap and clamps and, bypassed the heater core, making the connections from the back of the intake to the bottom of the water pump.One guy suggested blocking off both of these connections entirely and no one said that was good or bad. Does anyone have suggestions for me this spring?

[Old Goat 67]

You should go read this post real good:
http://forums.performanceyears.com/g...11&m=958104692
Bypassing the heater will NOT make any differance, I've done it too many times. Pull your pump and check the divider plate like George suggests. Works for me!
Charles