3 questions I couldn't answer in the archives (apologize for long post)...

1. Why are the heater hoses different sizes? Fluid isn't compressible and this is a closed loop. Hose size is a function of flow volume right? Anyone care to smarten me up? I cheated my way through HS Physics...;)

2. How difficult is it to braze AN couplings to the input/outlow lines? I was thinking a core that connected to a bulkhead fitting would be much better than the hose clamp fitting. I think I cracked a solder joint in my heater core when I was either pulling off or putting on the hoses. Grrrrrr. Just another thinking out loud question.

3. I'm gonna bypass my heater core until a later date. Since this is temp, I don't want to risk messing with the manf and pump bosses to plug them, so I'm just going run a hose from one to the other. Does the length of the hose matter? Under normal ops, the heater loop provides a place for trapped air, but if you bypass it, is just one of the heater hoses enough for the air, or does someone have a better idea?

Thanks,
Scott

Hey Scott, perhaps I can help.

1. While you are right, coolant is NOT compressible, the water pump is NOT a positive displacement pump either....it's a centrifugal type. This is inefficient compared to the positive displacement types of pumps and therefore hose size can affect flow rates. But, I don't know the conventional wisdom behind why there are everything from 1/2" to 3/4" either? Of course theoretically, you would size a heater for the size/volume of passenger compartment demand and physically design a core that could sustain a certain inside temperature at an ambient outside temperature with the available ...let's say 180 degree input to the heater. Therefore one would have to figure how much flow will be adequate to keep the core at that output.

2. I have seen AN connections and flared connections on heater cores before...it's quite common over on the streetrod side. So, you can do it pretty easily really.

3. Just plug the ports of the waterpump and inlet. Don't need a hose at all.

I would bet the only reason the hoses are differents sizes is to make it harder for the monkeys on the line to put them in the wrong place. Same reason the bolts on a steering ragjoint are different.

I'd have to disagree with you on the bypass, Jack... with the heater hoses plugged, there is no coolant moving at all if the thermostat ain't open, this can cause hot spots, even boiling around the exhaust ports when the rest of the engine is still cold. If you look at a BBC, or an Olds, they have a bypass connection from the pump to the intake to ensure some coolant is always moving. SBC don't.

I know it ain't no help for those solder joints, but I used Spectre cheapie braid and Pi-Thon fittings on my heater hoses. They seal good and look like real AN, without hassling with tube adapter fittings and for less than 50 clams per hose.

Drill a few holes in the T-stat to allow some water circulation before the thermostat fully opens.

that works

If you look at a BBC, or an Olds, they have a bypass connection from the pump to the intake to ensure some coolant is always moving. SBC don't.

Actually a small block has an "internal bypass". Ever wonder why there is an extra hole in the water pump and gasket on the passenger side of the engine? Thats because there is a bypass passage that runs through the block and up into the passenger side head. Check it out next time you look at a bare block.

Yes.....all small blocks have an internal bypass. So, no biggy blocking up the ports ..and I checked his post before I recommended that. BBC have to have a bypass or holes in the thermostat. I prefer the bypass hose because you compromise engine temperature management with holes in the very device that regulates the temperature!

Jim....I don't understand. What makes you think coolant moves with the thermostat closed and the heater circuit off too? No coolant flow there either?

The thermostat will/should open long before any hot spots happen with the proper anti-freeze mix and pressure capability.

The outlet hose from the core to the water pump is larger diameter so the unit pressure is always lower on the outlet side than the inlet side, to enhance continuous flow through the core; this is so the heat output is consistent so the driver doesn't have to fiddle with the temperature control all the time. GM heater hoses were both 5/8" until about 1958, when the change was made to the 3/4" outlet hose.

The heater circuit does serve as a bypass (except on A/C cars, which shut off the inlet hose when the A/C is on), but not having it isn't a problem; all small-blocks have a built-in internal bypass circuit in the passenger side leg of the water pump which pulls coolant out of the block into the inlet side of the water pump when the thermostat is closed - that's the "extra" hole you see below the main passage hole. Big-blocks don't have that internal bypass circuit, so that's why they all have the external bypass hose from the top of the water pump to the front of the intake.

The next question that always comes up is "Why is the heater core inlet always on the bottom and the outlet on the top?" That's done so the pulsations and any air bubbles in the inlet flow always enter the core a) "under water" and b) against a head of pressure, so there's a minimum of "burping" noise from the core that can be heard inside the passenger compartment. If the inlet was at the top, you'd hear a lot of pulsing noise all the time from the inside heater box. :)
:beers:

Actually a small block has an "internal bypass". Ever wonder why there is an extra hole in the water pump and gasket on the passenger side of the engine? Thats because there is a bypass passage that runs through the block and up into the passenger side head. Check it out next time you look at a bare block.

hmmm, learn something new every day! Always wondered (well not really) why that was there.:o