Hello,
Is bypassing the heater core to the rear of intake going to comprimise the motor from cooling properly? My heater core is shot and I have no time right now, putting away for winter - will deal with next spring. I'm taking a 3/4" x 5/8" reducer to run my 3/4" heater hose line from the bottom of water pump to the 5/8" nipple on the back of the intake. 65 LeMans 326 V8 with A/C (not hooked up) 2 spd with Edelbrock Performer Pontiac intake.
Thanks.
Rudy http://forums.performanceyears.com/g...s/icon_eek.gif

Hello,
Is bypassing the heater core to the rear of intake going to comprimise the motor from cooling properly? My heater core is shot and I have no time right now, putting away for winter - will deal with next spring. I'm taking a 3/4" x 5/8" reducer to run my 3/4" heater hose line from the bottom of water pump to the 5/8" nipple on the back of the intake. 65 LeMans 326 V8 with A/C (not hooked up) 2 spd with Edelbrock Performer Pontiac intake.
Thanks.
Rudy http://forums.performanceyears.com/g...s/icon_eek.gif

Rudy,

This is commonly done for your described purpose and to eliminate hot air inside of the car due to a failed water temp valve. There is no negative affect on engine cooling, save loosing the small radiator effect of the heater and that's only when it's being operated. http://pysales.com/images/sweat.gif http://pysales.com/images/sweat.gif

Les

66 GTO Coupe,455/trips,700r/2500stall,12bolt/3.08,1.79/13.01/104.5
68GP daily driver under restoration
--------------------------
Better lucky than good

i disagree. You are putting hot water from the rear of the engine, bypassing the heater core and then putting that hot water into the water pump directly. the heater core removes the heat from the water before returning it to the pump. No heater, no heat removal, so return water is still hot and it mixes with cooled water from the radiator at the pump, thereby heating up the water now going to the engine. Ask me how I know, since i bypassed a heater on the highway due to a leak, and then about 5 miles down the road, the engine overheats. Plugged off both lines, so no flow back to pump. Overheating problems solved.

Engineer,

Check out my post, I agree that the heater core provides additional cooling, but only when the water valve is opened. The heater outlet in the rear of the head is effectively "capped" when this valve is closed and the suction side of the water pump is open to the heater core.

If your car overheated due only to the heater core being bypassed, it would seem that your cooling system may be marginal. I can't see how a small amount of hot coolant introduced into the cold side (suction) of the water pump could be signifigant. I am glad that you found a solution to your overheating problem, many don't.

Les

66 GTO Coupe,455/trips,700r/2500stall,12bolt/3.08,1.79/13.01/104.5
68GP daily driver under restoration
--------------------------
Better lucky than good

Perhaps there was trapped air or just not enuf coolant in the system after the mishap. I also don't see how it would make a big difference at all.

George

rudy, i've done this "fix" repeatedly in the past with no problems.

the only way i could see this causing a problem would be if there was an air pocket in the head.

the heater can provide extra cooling in a overheat situation but should radiate much at all if it's in the off position.


mike

Rudy,

Mike and George bring up a good point re air trapped in coolant passages. This is one of the best reasons to utilize a coolant recovery system. As the system cycles between cold and hot temps any air trapped in the cooling system is automatically purged into the recovery bottle.

Les

66 GTO Coupe,455/trips,700r/2500stall,12bolt/3.08,1.79/13.01/104.5
68GP daily driver under restoration
--------------------------
Better lucky than good

Depending on how much work you want to do here is what I did. I removed the heater core, plugged the outlet on the timing cover fo the heater hose, and routed the water from the back of BOTH heads using the 301 nipples mack to the water crossover. Many have done this with excellent cooling results. Below is a pic of my setup before I put my intake on.

Honest dad, that 455 on the side of the block is a serial number http://forums.performanceyears.com/g...icon_smile.gif

67 that's a common mod for circle track cars and is good for some temp reduction on the street also.


mike

67 455 Bird nice mod for cooling. However, I have an old motor with an aftermarket intake and really don't know how or attempt and potentially costly modification to the old girl. How can I avoid or know if there is an air pocket in the head as you guys have mentioned since I certianly don't want to find out the hard way and have it overheat. I'm currently replacing the fan clutch. The only thing about the one I bought that I don't like is that the mounting flange has four open "U" shape cut outs in place of thru holes for the mounting bolts to attach the clutch to the water pump. It came with new bolts and split washers. What is the purpose or advantage to using the split washer over a solid washer?

Thanks.

Joe

Rudy,

See my post re coolant recovery system. This will eliminate trapped air.

The "U" shaped cutouts on your fan clutch are not a problem as the clutch registers to the water pump shaft. Use the flat washers to spread the load over the "U" shaped cutouts and place the split lockwashers over the flat in order to secure the fan clutch. Do not underestimate the damage that occurrs should this assembly come loose @ speed.

Les

66 GTO Coupe,455/trips,700r/2500stall,12bolt/3.08,1.79/13.01/104.5
68GP daily driver under restoration
--------------------------
Better lucky than good

some one needs to check something. Most of the older 65-67 A body cars do not have water valves in the heater hose lines. The ones on like 71-72 GPs only work if the AC is in the max. position. The idea of an air pocket in the system does not apply since that would mean the water pump with the bypass would be vapor locked, or cavitating which is not possible if you look at where the hot water return is compared to the suction on the timing chain cover. You are adding a lot of heat back into the pump. GM always had water flow through the heater. In fact, if an enigne is experiencing overheating, it is recommended to put the heat on high to help remove heat.

Since there is no air flow over the heater core when the air door is shut, the core reaches engine temperature and just becomes part of the plumbing without any heat transfer - so you should be able to just loop the heater hose with no loss in cooling since this is what is happening anyway during the summer.

And a question to ponder. Since you are short-cutting the normal cooling water route when you loop the heater hose outlet(s) to the manifold, why does this allow the engine to run cooler? The water would only be somewhat as hot since it has not done its full job on its way back through the head to the manifold crossover. Since our temp gauge is in the manifold, and it is getting cooler water from the short-cut, it will read cooler. But is the water at the front of the head actually running warmer since less volume is available across the front cylinders?

If you look at the picture again and then think about where the Water pump actually pulls water from, then you will see that he is feeding cooler water to both the front and the back of the heads at the same time. The water pump pulls from the block and with the cooler water going to the front and the back of the head I would think that all four corners of the block would run cooler then the center ie., 4,6,3,5. but I'm sure only slightly. I was going to do something like this on mine but I was going to feed both heads back to the water pump heater connection. remember that the water pump pushes water to the bottom of the radiator and then returns thru the upper hose back to the engine. I would be interested in tempetures taken at various points on the block to see whether there were (hot Spot's) in the block. Nice job though!! http://forums.performanceyears.com/g...icon_smile.gif http://forums.performanceyears.com/g.../icon_wink.gif http://forums.performanceyears.com/g...on_biggrin.gif http://forums.performanceyears.com/g...on_biggrin.gif

Sorry, I went out and re read the proper cooling circuit of a Pontiac and I stand corrected as to proper flow. Please disregard last post as just being tired and not thinking properly http://pysales.com/images/sweat.gif http://pysales.com/images/boxing.gif

looked at my 1967 gto with Air cond. heater box today and there is always an air flow over the core even if the air door is in the full cold position. the air door has a stop built in so there is always air across the core and therefore it will remove heat even in the full AC position. It would be nice if people looked at what they have instead of just talking. Bypass the heater and the car overheats.

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.THE HEATER CORE WAS NOT INCORPORATED INTO THE COOLING SYSTEM FOR ENGINE COOLING.IF YOU BYPASS HEATER CORE AND CAR OVERHEATS YOU HAVE A COOLING SYSTEM PROBLEM.

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? My door does close all the way. Must get awful hot in your goat during the summer. Possibly it is time to fix your door.

[This message was edited by lust4speed on December 01, 2003 at 09:33 PM.]

I bypassed my heater core on my 67 goat temporarily while I waited for my new core to come in and did not notice any temp increase without it...And I live in Texas and drove it in 5 o'clock traffic and it was 99 degrees that way.

Greg Bower

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.

"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.

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.

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.

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

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

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.

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

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?

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