Does it matter?

[custom10nut]

Does it matter which way the heater hoses are hooked up. The reason for asking is that I've seen it both ways. I would think the only effect would be which end of the heater core the water gets pumped into. I have mine , upper to upper, and lower to the water pump. In seems to work fine and there is no negative effect that I can tell.

[webfoot]

It matters a lot. one way you have water already cooled by the radiator going into the core, and the other way you get the hot water out of the engine going into the core.

How do I know this? I had the heater hooked up incorrectly on my chevelle for a few years, and always froze my bum off when driving in 40-50 degree temps to a St. Patty's day car show.

[truckster]

I think if you reverse them you get air conditioning.

I'm actually curious if there is a logical correct answer.

[1968aj]

now you have me thinking. which way is correct?

[geezer#99]

Intake to bottom of core gets the air bubbles out.
At least that's what I was told 50 years ago and done it that way since.

[leftybass209]

http://67-72chevytrucks.com/vboard/s...d.php?t=670195

this thread has some info from the GM service manual, as well as a pic of an original engine, and the service manual pic for routing.

[davepl]

Feed into the bottom so that the air gets pushed out. Feed from the pump side. Return (top) to intake. That would be the logical approach, I think.

[custom10nut]

Wow, look what I started. Webfoot makes perfect sense, but "pushing the air out" reasoning makes sense too. The whole reason for asks was that I saw pics of a truck that a member just bought, and in one of the pics it shows the hoses opposite to mine. I live down south so having water that's a little cooler in the heater core isn't an issue, like it would be in the northern climates. Most times I only use the defrost on chilly rainy days, because we all know these trucks will heat you out of the cab if you keep the fan on.

[AnotherWs6]

Hmmmm, there may be another reason why it matters. My truck has a shutoff valve installed in the (I believe with out checking) line going to the heater core. But even with that thing completly closed tight I still get some heat coming out. It makes sense that if the valve is installed on the output of the heater core some hot water can still be being pushed into the core. Or does it? It's about 107 degrees under the dash on a hot summer day with the AC (it's rear/roof only) blasting. Heater? Exhaust?

[1968aj]

I have 3 69 models. I went out to check and all 3 of them have the hose to the water pump going to the top fitting on heater core.

[custom10nut]

So, I guess I'll be switching my hoses.....

[davepl]

I only had the '69 Camaro assmebly manual handy, but it's showing pump to TOP inlet and then bottom outlet back to intake manifold! Does that mean the intake manifold port is the output, or does the output go to the top of the heater core?

Thinking about how the impeller works, I wonder if the pump fitting is indeed the return and the pressure side comes out of the intake manifold (like the thermostat, after all), which the goes to the bottom of the heater core. Also note that the hot water switch is in that bottom line.

That's my best guess, anyway: heater core fed at the bottom by the feed from the intake (not the pump as I had said earlier).

Below is the diagram, and for the heck of it a carefully restored Pontiac that I presume to be correct.

[webfoot]

That don't look like no pontiac!

[davepl]

Originally Posted by webfoot

That don't look like no pontiac!

'tis though, a 427 Astro Jet no less: See http://1969pontiac.com

[webfoot]

Ahh, the canuck models, that makes sense.

Looks real sweet under the hood!

[100%Chevy]

Looks like a 66,67 Chevy Impala to me!
The intake hose is pressure.The water pump hose is suction.
Your heater core should have a 5/8" tube and a 3/4" tube and hoses to fit.
Intake should be a 5/8" fitting and the pump should be a 3/4" fitting.
My 65 Impala----



Mike.

[57taskforce]

Dave your correct the manifold is the supply. when I hooked up the heater hoses in my 3100 with a 350, I used a gm radiator with a return and hooked the supply to the water pump. I couldn't get heat to save my life. I plugged the pump and ran the supply from the front intake port and wala, heat at last.

[firedemon]

any fitting on the water pump is an intake like the lower radiator hose the impeller pushes into the block and out the intake back to radiator and heater core usually lower so it dosent trap air and back to the pump from the top or it can return to radiator . I think it has something to do with how fast or how hot the water is depending where it returns but I am unsure

[100%Chevy]

Taking the water from the intake bypasses the thermostat,giving warm water to the heater sooner than waiting for the thermostat to open.
mike.

[davepl]

Why do big blocks have a bypass hose separate from the heater? You'd think the heater core accomplishes the same thing, but they seemed to feel the need. Sure there are vehicles without heaters, but they could have run the bypass hose in its place if that was the reason.

Anyone know its purpose?

[69chevytrucker]

funny both my heater hoses are diff sizes

[garyd1961]

Small block water pumps have bypass built in. I don't know about big blocks but some blocks don't have a place for the bypass, so it's pumping to a dead end. I know vortec engines are like this and maybe the 400 small block so they need a bypass hose.

[geezer#99]

Originally Posted by davepl

Why do big blocks have a bypass hose separate from the heater? You'd think the heater core accomplishes the same thing, but they seemed to feel the need. Sure there are vehicles without heaters, but they could have run the bypass hose in its place if that was the reason.

Anyone know its purpose?

Smallblock has a built in bypass in the pump that allows coolant back into the pump inlet. Bigblock has a bypass hose. Designed that way because some vehicles had a heater delete and no core. As well as some that had the valve in the bottom hose to the core.

[davepl]

Originally Posted by geezer#99

Smallblock has a built in bypass in the pump that allows coolant back into the pump inlet. Bigblock has a bypass hose. Designed that way because some vehicles had a heater delete and no core. As well as some that had the valve in the bottom hose to the core.

Thank you sir... You'd think, being a newer design, that it'd be cheaper and more reliable and fewer parts involved to do it like the small block with the integral bypass. Odd that they chose to add more parts, complexity, and another cooling system failure point.

Any advantage to the hose style that you can think of that makes it preferable to the pump-integral kind?

[geezer#99]

Originally Posted by davepl

Thank you sir... You'd think, being a newer design, that it'd be cheaper and more reliable and fewer parts involved to do it like the small block with the integral bypass. Odd that they chose to add more parts, complexity, and another cooling system failure point.

Any advantage to the hose style that you can think of that makes it preferable to the pump-integral kind?

Wasn't really a newer design as the 1958 W motor had the same bypass as the later mystery 427 and it's offshoots.
Likely just a cost per unit thing. Or maybe the need for better water flow. Or a better way to minimize pump cavitation.