Help!! :)

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77georgec

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So last year i had the privelege of buying a 1986 k10. The 4.3 engine was swapped with a crate zz4 (350). When i brought the truck home i noticed that the heat didn’t work so i went about the process of rewiring it and attaching all the vacuum lines back up. Heater blower motor comes on and blows through the vents. The issue i am having is that the hoses running from the heater core are both cold, even after letting the truck idle. The top radiator hose running to the block is hot. Feels like the water isn’t circulating? Could it be the water pump possibly?
 

77georgec

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I also just finished flushing out the heater core a few minutes ago… still nothing
 

Bextreme04

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I also just finished flushing out the heater core a few minutes ago… still nothing
Pics? How do they have the hoses run? You should have the outlet from the intake manifold on the engine to the heater core. The return from the heater core should then go to either the radiator or the water pump. Were you able to flow water through the heater core with both lines disconnected? If nothing flowed through, that would mean it's plugged and that would be why both lines are cold(not likely). The other explanation for both lines being cold would be that you have both lines to a suction source(one line to radiator and the other to the water pump), this is the most likely and common thing that happen in a motor swap. Proper operation would have the feed line very hot and return line to the radiator or pump being warm with very hot air blowing in the cab.
 

77georgec

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Top hose goes to radiator. Im also noticing that the bottom large hose on the radiator isn’t getting warm either.
 

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77georgec

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Truck isn’t overheating and i bled the air out of the system.
 

77georgec

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Second heater core line does go right to the water pump
 

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77georgec

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So basically what im gathering is i need to move the heater core hose from the water pump to the intake. Should i just buy plugs to put in the place of the hose on the water pump? The hose that is currently on the intake runs directly into the water pump as well.
 

Bextreme04

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So basically what im gathering is i need to move the heater core hose from the water pump to the intake. Should i just buy plugs to put in the place of the hose on the water pump? The hose that is currently on the intake runs directly into the water pump as well.
Yes, that is your problem. Someone didn't know what they were doing when they swapped in that motor. You need to cap both of those inlets into the pump. Get rid of the hose from the intake manifold to the water pump. Connect heater hose directly to the connector on the intake. This will still allow the coolant to circulate through the engine and heater core without the thermostat being open(that's what someone was trying to do with that hose routing). The current hose routing has coolant going from the intake to water pump under pressure in a constant loop and the heater core is going from suction to suction, so you get no flow.
 

Bextreme04

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Technically if you want to just test it out before making a permanent fix or if you don't have a way to plug the water pump right away, you could just do a quick check by:

Unhook the heater line from the water pump.
Disconnect the line from the water pump to the intake manifold(at the intake manifold), and then just loop the water pump to water pump(the port that you just unhooked the heater line from) using that line.
Connect previously disconnected heater hose line to Intake manifold fitting.

That should get you a hot blowing heater and restore proper coolant flow through the engine. If everything checks out you can then go to the hardware store and get the correct sided NPT plugs to block off those holes.
 

77georgec

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You guys are absolutely awesome :) i will do that.
 

DoubleDingo

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@Bextreme04 Couldn't the bypass remain in place, just make sure the inlet hose to the heater core comes off the intake? And the other goes to the water pump. And of course the outlet hose from the core goes to the radiator just like it already is.
 

DoubleDingo

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Upon closer inspection, it appears there are two hoses coming from the water pump? Looking at the zz4 350 on the innerwebs, there appears to be a bypass port in the intake, as well as the heater nipple port.

http://gmhorsepower.com/350-ZZ4-Base.php
 

77georgec

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Yes there are two hoses coming off the water pump. One is the heater core hose and one is routed to the intake
 

77georgec

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Should i just plug both the ports on the water pump and run the heater core to the intake?
 

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