I am adding a heater control valve to a TPI swapped system that did not originally have one. I am NOT re using the TPI oil cooler, and I am bypassing the TB coolant passages. So here is what I understand: the heater control valve gets vacuum in AC mode from the climate control (check). The coolant port on the side of the valve that only has one port would have connected to the valve body coolant passage outlet, but in my case it will connect directly to the manifold coolant outlet (check). Now I am left with the 2 coolant ports on the valve that face the firewall. One must go to the inlet of the heater core (which one?) and what does the other one go to?? And I assume the "outlet" side of the heater core returns directly to the coolant port at the top passenger's side of the radiator? Thanks! Steve

 

Normally the heater outlet has a curved hose that runs the water down into a metal tube that runs along the frame rail on the way back to the radiator. Halfway back to the rad, there is another inlet to that tube that the other port on the valve feeds through a hose when it is bypassing the heater core. So if the valve is one way, the water goes through the heater core and back to the radiator. If the other way, it bypasses the heater, goes down to that tube and returns to the radiator. Bottom outlet to heater core, top to bypass hose

 

Ok thanks for the great explanation. That leaves me with one more question...where does the outlet from the heater core go if the heater core, when bypassed, goes back through this tube to the top of the radiator?

 

They both feed the same tube that has the two inlets, one at the heater end and the other in the middle, and then goes toward the radiator and ends with heater hose finishing the trip to the radiator. Does that help?

 

Yes I know exactly which tube you are talking about now and how it's routed. I have multiple TPI setups in the basement but am only now getting around to actually using the stock heater hose routing, I had that setup to have the heater core on at all times before and did not have the oil cooler hooked up. Thanks again. Steve

 

I just had an epiphany of WHY the TPI cars have the 3 way heater valve....because of accessories like the oil cooler and TB preheater on the bypass loop w/ the heater core, if you simply had an on/off heater valve that when off, totally blocked water through the core and therefore broke the bypass loop, your TB preheater and oil cooler would become useless due to losing all flow through them. The 3 way heater valve allows those parts to maintain coolant flow even when the heater core is taken out of the loop...suddenly it all makes sense now. Thanks again for the explanation, I will get this thing plumbed up properly now.

 

I have a 87 5.7 tpi that I recently put and edelbrock intake, a bbk 52 tb and comp cam 1.6 roller rockers. While I was at it I took my ac out cuz I live in Canada and wanted to clean up the engine compartment a bit. And now I'm stuck in defrost with not vacuum to change settings or turn it off. Do any of you guys know how this can be fixed? Rob vacuum from somewhere maybe?