ssleeper
Active Member
Putting this in General car talk to hopefully get the most views. Sorry for the long post...I very much appreciate any help!
I'm at my wits end...maybe I'm overthinking this. I have a 357 small block (+.040") in my '61 which was rebuilt last year. The water pump is new (Proform aluminum) and is the correct rotation, the radiator is a new 4 core HD "409" from Cool Craft, the thermostat is a Mr. Gasket high flow style 180 degree that was tested in boiling water before it was installed, all hoses are new, radiator cap is a 13#, it does have an overflow tank hooked up, and it has Derale single electric fan (dual speed) with aluminum shroud that is sealed to the radiator and move a ton of air. Low fan set to come on at 170, high fan set to come on at 185, which they do. I have a dakota Digital fan controller which reports accurate temps and a mechanical Stewart Warner gauge which is within ~5 degrees of the Dakota Digital readout. Both gauge senders are in the same coolant port in the intake.
With the heater core bypassed (hoses looped together,) it runs at 180-185 on the gauge, even after I beat on it. All seems normal. But, when I hook up the heater core, the temps jump and swing wildly over 220 degrees. The odd thing is the temps come down when I turn the heater control valve off and then they go wild again when I turn the heater valve on. The heater core and water valve are originals. The 5/8" hose comes from the intake manifold to the 5/8" port on the control valve. I have a pre-moulded (reproduction) hose that goes from the valve to the bottom connection on the core, and then I have a 3/4" hose going from the top/outlet of the core to the port on the water pump. I used to have a crossover in the heater hoses but left it out this time as it doesn't seem to make any difference and the I6/small block cars did not come from the factory with one anyway.
The heater core does not leak and it is not restricted. I flushed it in both directions with it out of the car and pressure tested to 15psi which it held all day submerged in water. I've also used one of the Lisle coolant burp kits that go in place of the radiator cap when filling the system to let air purge out as the engine runs, but with and without the heater valve open. I've also jacked up the front of the car to make sure the radiator cap is the highest point (the car is lowered).
My gut says it's air in the system, but after running the engine at various RPMs for 10-15 minutes, I'm not seeing any air bubbles coming up into the Lisle funnel and then all of sudden I get a geyser of coolant boiling all over. Temps at this point are showing 210-230 on the gauge. If I close the heater valve, the temps will fall rapidly to ~170 or so...if I open the valve...they skyrocket again. I've tried purging the air a half dozen times and nothing I do seems to make any difference. Coolant in green 50/50 mix.
What gives!? I've never had this much trouble, especially since it's just a small block with the stock heater components.
I'm at my wits end...maybe I'm overthinking this. I have a 357 small block (+.040") in my '61 which was rebuilt last year. The water pump is new (Proform aluminum) and is the correct rotation, the radiator is a new 4 core HD "409" from Cool Craft, the thermostat is a Mr. Gasket high flow style 180 degree that was tested in boiling water before it was installed, all hoses are new, radiator cap is a 13#, it does have an overflow tank hooked up, and it has Derale single electric fan (dual speed) with aluminum shroud that is sealed to the radiator and move a ton of air. Low fan set to come on at 170, high fan set to come on at 185, which they do. I have a dakota Digital fan controller which reports accurate temps and a mechanical Stewart Warner gauge which is within ~5 degrees of the Dakota Digital readout. Both gauge senders are in the same coolant port in the intake.
With the heater core bypassed (hoses looped together,) it runs at 180-185 on the gauge, even after I beat on it. All seems normal. But, when I hook up the heater core, the temps jump and swing wildly over 220 degrees. The odd thing is the temps come down when I turn the heater control valve off and then they go wild again when I turn the heater valve on. The heater core and water valve are originals. The 5/8" hose comes from the intake manifold to the 5/8" port on the control valve. I have a pre-moulded (reproduction) hose that goes from the valve to the bottom connection on the core, and then I have a 3/4" hose going from the top/outlet of the core to the port on the water pump. I used to have a crossover in the heater hoses but left it out this time as it doesn't seem to make any difference and the I6/small block cars did not come from the factory with one anyway.
The heater core does not leak and it is not restricted. I flushed it in both directions with it out of the car and pressure tested to 15psi which it held all day submerged in water. I've also used one of the Lisle coolant burp kits that go in place of the radiator cap when filling the system to let air purge out as the engine runs, but with and without the heater valve open. I've also jacked up the front of the car to make sure the radiator cap is the highest point (the car is lowered).
My gut says it's air in the system, but after running the engine at various RPMs for 10-15 minutes, I'm not seeing any air bubbles coming up into the Lisle funnel and then all of sudden I get a geyser of coolant boiling all over. Temps at this point are showing 210-230 on the gauge. If I close the heater valve, the temps will fall rapidly to ~170 or so...if I open the valve...they skyrocket again. I've tried purging the air a half dozen times and nothing I do seems to make any difference. Coolant in green 50/50 mix.
What gives!? I've never had this much trouble, especially since it's just a small block with the stock heater components.
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