Possible heater core bypass fix?

[mbouse]

hey cdcnclipper... stop up to the introduction section and tell us about yourself. it's great to have you on board, but no one will know you're here (properly) until you post there.

[MikeysFiat]

This thread is 2 years old, but still on point.

I purchased a 1972 Spider. The heater is bypassed. My plan is to repair the heater and defroster as part of the restoration. After reading this thread I am wondering if the bypass is a fix the enhance engine cooling, or simply a method to bypass a malfunctioning heater.

I like the 3-way valve with purge/flush port idea. It's simple and makes perfect sense to ensure adequate coolant flow.

Any help is greatly appreciated.

BTW, I live in El Paso TX. ..gets hotter than hell here in the summer. I'd hate to over heat my new project.

[reinaldo]

I guess it's a good idea to get a replacement heater control valve. If it will not work, maybe you really needed a new heater core.

[131]

[kmead]

Although a heater core bypass may have some benefit, I have never heard of the heater core water flow (or lack of it) being a contributor to any systemic head gasket failure.

The heater line pulls from the top gallery that goes across the tops of the head and wasn't designed to be part of the exit flow from that area as part of the primary cooling of the engine. I would actually question the value of bringing the hot coolant directly from the top of the head into the cold coolant intake at the back of the water pump, displacing that amount of cooled coolant being distributed into the engine. I would bet it would actually create a situation where the engine could run hotter as you are mixing increasingly hot coolant back into the engine without it being run through the radiator.

What I have seen time and again is a failure to properly get all of the air out of the system which can be made more difficult by the heater return line being the highest point in the system, particularly on the later cars with the three way thermostat. Adding the Prestone bleed to the high point of the heater hot water feed line will ensure all the air is gotten out of the head and heater core.

Before installing the bypass I would think very carefully about the actual water path through the entire system before making changes the engineers did not choose to make in the first place. Given the change to the later thermostat solution they were definitely looking at ways to manage initial warm up and cooling, had there been benefit in a simple three way valve I am sure they would have done so.

[zachmac]

As the original poster of this thread I feel obligated to jump in as many of you may not have bothered to read from the start:

I was WRONG in my inital assumptions and ideas about the flow path and there is NO NEED to create any sort of bypass flow path for when the heater valve is closed as it is already there via small secondary lines (at least on my 1980 FI car). I was just new and stupid two years ago and failed to recognize it before I really tore into the system. I think the stock setup with the addition of the Prestone bleed connector in the high point is all you need or should do. Sorry if my initial ignorance has caused confusion.

[MikeysFiat]

Zach, no sweat. To err is human. After I obtained a service manual and read the cooling specs, I decided to forego the 3 way bypass and restore the system as designed. My heater and defroster work very well. Engine water temp is significantly cooler with heater on, for obvious reasons. I drive 40 miles, one way to work (6 street lights within the first five miles - then open roads). I have ample time to monitor and study the engine performance. The somestimes annoying constant heat can be avoided by opening the fresh air duct behind the fuse box, but then again it's winter here albeit a mild one.