strange cooling problem
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Is your lower (suction) radiator hose a 'rigid' design which prevents collapse or does it have the anti-collapse spring installed inside?
If not, the harder the pump works to suction fluid from that hose, the more it would collapse and limit flow to the pump. This is a common problem with the 'excessive heating at elevated speeds' problem.
If not, the harder the pump works to suction fluid from that hose, the more it would collapse and limit flow to the pump. This is a common problem with the 'excessive heating at elevated speeds' problem.
Thread Starter
Intermediate
Joined: May 2000
Posts: 36
Likes: 6
From: Hazelwood MO
Thread Starter
Intermediate
Joined: May 2000
Posts: 36
Likes: 6
From: Hazelwood MO
Is your lower (suction) radiator hose a 'rigid' design which prevents collapse or does it have the anti-collapse spring installed inside?
If not, the harder the pump works to suction fluid from that hose, the more it would collapse and limit flow to the pump. This is a common problem with the 'excessive heating at elevated speeds' problem.
If not, the harder the pump works to suction fluid from that hose, the more it would collapse and limit flow to the pump. This is a common problem with the 'excessive heating at elevated speeds' problem.
Thread Starter
Intermediate
Joined: May 2000
Posts: 36
Likes: 6
From: Hazelwood MO
Thanks to all who contributed and helped try to solve this little bump in the road. Time's up for today so 'til we meet again, thanks again and keep the rubber side down. 
oldguy (other wise known as Jim)
oldguy (other wise known as Jim)
Team Owner
Joined: Mar 2002
Posts: 44,674
Likes: 1,830
From: Huntsville AL
I understand what you are saying and seeing but water not flowing through the heater core will not cause the water pump to lock up. You could disconnect and block off both inlet and outlet hoses (same as a shutoff valve) and the water pump will still pump water through the block.
Think of cars that had a "Heater Delete" option.
Think of cars that had a "Heater Delete" option.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The thermostat is the most likely cause, given the info you have provided. It is probably closed and under idle conditions will stay closed and cause overheating. When you begin driving, the added pressure from the water pump may cause the stat to open a bit and allow the temps to drop some. If the stat locks in at that point, further increase in engine speed would cause further heating.
When you turn the heater on high, the water line from the pump is direct...it doesn't flow through the stat; so it takes a significant portion of the heat and dumps it, causing the temps to drop.
Makes sense to me.
Thread Starter
Intermediate
Joined: May 2000
Posts: 36
Likes: 6
From: Hazelwood MO
The thermostat is the most likely cause, given the info you have provided. It is probably closed and under idle conditions will stay closed and cause overheating. When you begin driving, the added pressure from the water pump may cause the stat to open a bit and allow the temps to drop some. If the stat locks in at that point, further increase in engine speed would cause further heating.
When you turn the heater on high, the water line from the pump is direct...it doesn't flow through the stat; so it takes a significant portion of the heat and dumps it, causing the temps to drop.
Makes sense to me.
Where I have a problem with this is that in order for the heater core to remove THAT much heat that quickly it would need to be as big as the radiator. 
The ONLY route to the rad is thru the stat. The cooling system works very well, when the heater core is in the circuit, so the thermo MUST be open for it to even work at all. No? It seems to come down to WHERE THE HELL IS MY BY-PASS? Do big blocks run the same way if that external by-pass hose is missing or blocked some way? If so, what is so different about this normally configured SBC block, heads, water pump,thermo, fans et al that it must have the heater core in the circuit to cool. Which it does. Very well. Any ideas from some big block guys on this by-pass thing?
I welcome any input to help put the worms back in the can.
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Burning Brakes
Joined: Apr 2008
Posts: 1,222
Likes: 93
From: shelbyville West Michigan
so is it a bb or sb? sb has bypass built-in the block (that extra hole where the pump mounts).
big blocks MUST have the upper hose connected for bypass.
see pics, it is possible someone blocked the block or the water pump if a SB
big blocks MUST have the upper hose connected for bypass.
see pics, it is possible someone blocked the block or the water pump if a SB
Thread Starter
Intermediate
Joined: May 2000
Posts: 36
Likes: 6
From: Hazelwood MO
We shall see what we shall see. Thanks much.