The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - 55.2-59 Heater Hose Ideas

1project2many · 05-10-2020, 08:38 PM

Ok, I'm gonna be that guy.

On first generation SBC's running pre-Vortec cylinder heads there is a coolant bypass passage built into the RH head and RH side of the block. This passage allows some coolant to circulate through the block and back to the water pump at all times but does not direct any coolant through the intake manifold. Early SBC equipped vehicles such as the TF truck had a heater hose connection at the front of the intake below the thermostat. When coolant was allowed to circulate through the heater this would allow warming water from the engine to contact the thermostat and warm it up so it would open.

Many of these vehicles used a manual shutoff valve which completely blocked coolant flow through the heater. When the valve and thermostat were closed the temperature could spike as the engine warmed up. The fix for many was to drill a small hole in the thermostat or to use a "premium" thermostat which had a very small leak built into the t-stat.

Over the years GM altered the heating system flow path. They moved the heater connection to the RH side of the intake and removed the shutoff valve allowing coolant to circulate continuously through the heater. They changed the controls in the heater so air was directed around the heater core. This change allowed coolant to circulate to the top of the intake and signal the t-stat to prevent delayed circulation through the radiator.

Vortec engines completely changed the cooling bypass system. Vortec uses a dual valve T-stat which opens the bypass when it closes off the radiator. The bypass is connected between front of intake and water pump. This system improves engine cooling by (1) providing a strong signal to the thermostat, and (2) preventing coolant from bypassing the radiator when the engine is warm. Because of this change the hole in the block has been deleted. Which has led to some water pumps being remanufactured using housing not containing the passages for the gen 1 SBC bypass.

Hopefully you have no problems but if you do, the description may help figure things out. In your case removing the hoses and putting in plugs should work. It looks like you have a "Gen 1" block and heads. Hopefully the water pump is drilled and the proper gaskets are installed. If you have trouble with the temperature rising high before the thermostat opens try drilling a small hole in the 'stat.

05-10-2020, 08:38 PM	#11
1project2many Registered User Join Date: Mar 2012 Location: Lakes Region NH Posts: 3,158	Re: Heater Hose Ideas Ok, I'm gonna be that guy. On first generation SBC's running pre-Vortec cylinder heads there is a coolant bypass passage built into the RH head and RH side of the block. This passage allows some coolant to circulate through the block and back to the water pump at all times but does not direct any coolant through the intake manifold. Early SBC equipped vehicles such as the TF truck had a heater hose connection at the front of the intake below the thermostat. When coolant was allowed to circulate through the heater this would allow warming water from the engine to contact the thermostat and warm it up so it would open. Many of these vehicles used a manual shutoff valve which completely blocked coolant flow through the heater. When the valve and thermostat were closed the temperature could spike as the engine warmed up. The fix for many was to drill a small hole in the thermostat or to use a "premium" thermostat which had a very small leak built into the t-stat. Over the years GM altered the heating system flow path. They moved the heater connection to the RH side of the intake and removed the shutoff valve allowing coolant to circulate continuously through the heater. They changed the controls in the heater so air was directed around the heater core. This change allowed coolant to circulate to the top of the intake and signal the t-stat to prevent delayed circulation through the radiator. Vortec engines completely changed the cooling bypass system. Vortec uses a dual valve T-stat which opens the bypass when it closes off the radiator. The bypass is connected between front of intake and water pump. This system improves engine cooling by (1) providing a strong signal to the thermostat, and (2) preventing coolant from bypassing the radiator when the engine is warm. Because of this change the hole in the block has been deleted. Which has led to some water pumps being remanufactured using housing not containing the passages for the gen 1 SBC bypass. Hopefully you have no problems but if you do, the description may help figure things out. In your case removing the hoses and putting in plugs should work. It looks like you have a "Gen 1" block and heads. Hopefully the water pump is drilled and the proper gaskets are installed. If you have trouble with the temperature rising high before the thermostat opens try drilling a small hole in the 'stat.