Correct heater hose routing

[fast72beeper]

What is the correct way to route heater hoses on a SBC? Currently I have the feed coming off of the water pump and the return goes to the radiator. Heater is not getting hot, just lukewarm. Should it be fed off of the intake?

Also, is the bigger hose return or feed and does it matter?

Thanks

[88Jimmy4x4]

Originally Posted by fast72beeper

What is the correct way to route heater hoses on a SBC? Currently I have the feed coming off of the water pump and the return goes to the radiator. Heater is not getting hot, just lukewarm. Should it be fed off of the intake?

Also, is the bigger hose return or feed and does it matter?

Thanks

Ya you have it swapped around somewhat, 3/4" hose to radiator or water pump and 5/8" hose to intake no matter what.

this from my GM manual

[chengny]

You are getting basically no water flow through the heater core. The nipple on the water pump can be used in place of a nipple at the top of the radiator tank - but not in conjuction with it.

That nipple is on the suction side of the water pump. So what you are doing is sucking water from the bottom of the heater core and trying to replace it with the steam/vapor that exists at the top of the radiator tank. Although that vapor is hot, compared to water it has little BTU value.

The area of the cooling system that heats up first and gets the hottest is at the outlets of the cylinder head cooling passages. These connect directly to the intake manifold. Also, and more importantly, is the fact that this area is on the discharge side of the water pump - consequently it is at the highest pressure. That is the reason that the inlet to the heater core is supplied from the inlet manifold.

That hose (from the intake manifold) should always be connected to the bottom of the heater core. As the coolant flows into the core it fills it from the bottom to the top (where the outlet hose is connected). This ensures that the tubes within the heater core are always full of water and any entrained air (that would impede heat transfer) is vented out along with the coolant that is headed back to the engine.

That is why, if you have the option, it is always best to connect the return from the heater core to the radiator tank.

[Malibu 496]

I just bought a 87 blazer plow truck with a 350 tbi that has the hoses on the water pump and the radiator, I wanted to switch it but the intake doesnt have a spot for a nipple to be installed was there another place that these motors had to hook up the inlet hose for the heater?

[gchemist]

If you want the hottest water through the core, use a port at the back of the intake. A front intake port will work too. The cab is small enough heat is no problem with the correct hose routing. In less than 0.75 miles, my truck is HOT!!

[wilkin250r]

Originally Posted by Malibu 496

I just bought a 87 blazer plow truck with a 350 tbi that has the hoses on the water pump and the radiator, I wanted to switch it but the intake doesnt have a spot for a nipple to be installed was there another place that these motors had to hook up the inlet hose for the heater?

Does your heater work? It sounds like you have the same setup as the original poster, and I just can't see how that would work.

Most all hose connections on the water pump are INLET connections, meaning water is supposed to flow IN to them, not out. The outlet side of the water pump is the engine block. So you have an inlet connected to an inlet, there is very little pressure difference there to create flow.

And it begs the next question, how does your intake manifold not have a spot for a nipple? I have a couple on mine.

I suppose if you're really desparate to fix it without replacing the entire intake manifold, you could always get a new thermostat housing with a spot for a nipple. It's certainly not the best, because you won't get any flow or heat until after the thermostat opens up, but it would be a cheap solution.

[wilkin250r]

With a little more research, I came across and even better idea. Perhaps you can find something like this, a Thermostat Housing Spacer. I'm not sure what the size of the threaded holes are, but it would allow you to put the thermostat ABOVE the two outlets, and thus you would get water flow (and thus heat to the heater core) out of them even if the thermostat was closed.

I can't give you the origins of this part, because it was just on a site full of pictures, not engine parts. But you get the idea, with a little bit of research you might be able to find something that would work for you.

[Redcap]

There is always drilling and tapping one of the bosses case into the intake, if it has them.

[Malibu 496]

I did some checking and found a boss on the rh rear of the intake but the previous owner covered it with epoxy. I might try drilling and tapping the front coolant passage or do the thermostat adapter.

[chengny]

Most SBC's have an unused 1/2" NPT tapped port on the RH cylinder head. It's in the same position as the opening for the coolant temperature sender on the LH head. But since it's on the RH side - it is between 6 & 8 rather than 1 & 2.

That should heat up pretty quick and it is on the high pressure side of the system.

[88Jimmy4x4]

Originally Posted by Malibu 496

I did some checking and found a boss on the rh rear of the intake but the previous owner covered it with epoxy. I might try drilling and tapping the front coolant passage or do the thermostat adapter.

To drill and tap your intake your gonna have to remove it, might as well buy one that has the port already like an edlebrock.

[SonomaComa]

Originally Posted by chengny

You are getting basically no water flow through the heater core. The nipple on the water pump can be used in place of a nipple at the top of the radiator tank - but not in conjuction with it.

That nipple is on the suction side of the water pump. So what you are doing is sucking water from the bottom of the heater core and trying to replace it with the steam/vapor that exists at the top of the radiator tank. Although that vapor is hot, compared to water it has little BTU value.

The area of the cooling system that heats up first and gets the hottest is at the outlets of the cylinder head cooling passages. These connect directly to the intake manifold. Also, and more importantly, is the fact that this area is on the discharge side of the water pump - consequently it is at the highest pressure. That is the reason that the inlet to the heater core is supplied from the inlet manifold.

That hose (from the intake manifold) should always be connected to the bottom of the heater core. As the coolant flows into the core it fills it from the bottom to the top (where the outlet hose is connected). This ensures that the tubes within the heater core are always full of water and any entrained air (that would impede heat transfer) is vented out along with the coolant that is headed back to the engine.

That is why, if you have the option, it is always best to connect the return from the heater core to the radiator tank.

Thanks for the info. Mine does not have A/C. For some reason I thought the Heater Core would be treated just like the Radiator, Have hot fluid travel from the Top to the Bottom of the Heater Core. That way if it wasn't totally 100% full it would not just blow bubbles.
I have getting all kinds of mixed reviews on this matter totally opposite of each other. I was handed a box with a new Heater Core and Blower Motor in it when I purchased my 1970 GMC C-20 as it was not hooked up when I purchased it. I came to this site to see the proper way to install it.
I new the pressure side is on the Intake Manifold and the suction side came from the Water Pump but what one should be on the Top is the dilemma. Here is a couple of pictures I found on this site.

[beamn7]

Originally Posted by Malibu 496

I did some checking and found a boss on the rh rear of the intake but the previous owner covered it with epoxy. I might try drilling and tapping the front coolant passage or do the thermostat adapter.

That's correct. The TBI intakes moved the heater hose connection to the pass. side rear of the intake above #8. From the factory they were a quick connect style metal pipe / connector set up that was very prone to leaking and corrosion. Plenty of these ended up removed and a standard nipple installed with bulk heater hose rather than the factory pre-formed hose / metal pipe set up. I would not recommend drilling and tapping that with the manifold installed. Pick up and Edelbrock manifold and a heater hose nipple and call it a day.

[chengny]

I new the pressure side is on the Intake Manifold and the suction side came from the Water Pump but what one should be on the Top is the dilemma.

In any shell & tube or finned tube type heat exchanger (where the inlet and outlet nozzles are at opposite ends of the vertical plane), the flow of liquid should - whenever possible - be: in through the bottom and out from the top.

This arrangement accomplishes two things:

1. Since the liquid level has to completely pack the shell before it can exit out the top, it ensures that the shell is continuously being purged of any entrained air.

2. It also helps the tube surfaces receive the maximum amount of possible contact with the heating/cooling medium (this is also the reason that the two nozzles are offset from each other). If the flow was from the top down, it presents the possibility of "laning". IOW - the fluid could possibly just shoot right down the middle and never even contact much of the tube surfaces. With the openings for the inlet/outlet on opposite sides of the water boxes - and the medium required to overcome gravity - stagnant pockets within the area of flow are reduced.





For some reason I thought the Heater Core would be treated just like the Radiator, Have hot fluid travel from the Top to the Bottom of the Heater Core. That way if it wasn't totally 100% full it would not just blow bubbles.


The key difference here is that the flow through these types of radiators is of the horizontal crossflow design - as opposed to a heater core, where the flow is in the vertical direction (from bottom to top).

So even though - it appears from the arrangement of a radiators inlet/outlet nozzles - that the coolant flow is vertical (and from the top to the bottom), it isn't like that.

In actuality the flow through a radiator is from left to right. At it's most basic, a radiator is simply two vertically oriented tanks that are inter-connected by a series of tubes. The tubes are fitted with fins on the airsides to increase their effective surface area.

As the water pump circulates the engine coolant through the system, it forces the liquid to move from the inlet tank, through the tubes and then over into the outlet tank. The vast majority of the heat exchange done by the radiator occurs as the coolant passes through the finned tubes.

The main reason that the outlet is located as far down on the outlet tank as possible is to keep the inlet to the water pump's suction hose as submerged as possible. This provides the pump with a supply of liquid for as long as possible in the event of a major loss of coolant.