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I'm trying to determine what's causing my engine to run hot. I've got the radiator off and the thermostat out. I ran the following test: connected a water reservoir to the pump inlet hose and connected a hose on the other side of the thermostat housing. Ran the engine, and the pump only produced a very small flow rate. How much water should the pump be moving, and how can I tell if the pump or impeller are shot? Thanks....
 
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japgen said:
I'm trying to determine what's causing my engine to run hot. I've got the radiator off and the thermostat out. I ran the following test: connected a water reservoir to the pump inlet hose and connected a hose on the other side of the thermostat housing. Ran the engine, and the pump only produced a very small flow rate. How much water should the pump be moving, and how can I tell if the pump or impeller are shot? Thanks....
dont know but if you figure there is only 2.2 or so quarts of coolant in there I would think you dont have very high flow.
 

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"Small flow" is pretty vague. The pump should produce a steady stream, guessing from the impeller size, between a quart and a half gallon per minute at idle.
 
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andyauger said:
"Small flow" is pretty vague. The pump should produce a steady stream, guessing from the impeller size, between a quart and a half gallon per minute at idle.
water pump turns half a turn for each crank revolution.
 

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Let me expand a bit. The water pump is a centrifugal design. It's throughput is dependent on differential pressure and the speed at which it rotates. Other factors that affect performance are the clearances between the impeller and the housing, the condition and shape of the outlet "cut water", wear on the impeller and/or the housing (increasing clearance). The viscosity and specific gravity of the liquid make a difference. You can't look at it and know what the pumping rate should be. Experience tells me that a pump this size turning at, say, 1,500 RPM should be able to move about a quart a minute pretty easily. It could move a lot more, say a gallon per minute. Most water pumps have a lot of "slip" built into them (they aren't designed to be very efficient) because much of the time they have to rotate "dead headed" (no flow). The more efficient the pump the worse it suffers at dead head conditions. Cooling pumps don't have to move a lot of liquid, and they don't have a lot of pressure to overcome. The limit is the cooling capacity of the radiator. Interestingly, sometimes removing the thermostat on some engines makes them overheat. There isn't enough "residence time" in the radiators for effective heat transfer. The hot liquids go in and right back out before they loose any heat.

Try pumping water with the pump only as you described, and time how long it takes to pump a quart at idle. If you are moving a quart or more you are probably O.K.
 

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andyauger said:
Let me expand a bit. The water pump is a centrifugal design. It's throughput is dependent on differential pressure and the speed at which it rotates. Other factors that affect performance are the clearances between the impeller and the housing, the condition and shape of the outlet "cut water", wear on the impeller and/or the housing (increasing clearance). The viscosity and specific gravity of the liquid make a difference. You can't look at it and know what the pumping rate should be. Experience tells me that a pump this size turning at, say, 1,500 RPM should be able to move about a quart a minute pretty easily. It could move a lot more, say a gallon per minute. Most water pumps have a lot of "slip" built into them (they aren't designed to be very efficient) because much of the time they have to rotate "dead headed" (no flow). The more efficient the pump the worse it suffers at dead head conditions. Cooling pumps don't have to move a lot of liquid, and they don't have a lot of pressure to overcome. The limit is the cooling capacity of the radiator. Interestingly, sometimes removing the thermostat on some engines makes them overheat. There isn't enough "residence time" in the radiators for effective heat transfer. The hot liquids go in and right back out before they loose any heat.

Try pumping water with the pump only as you described, and time how long it takes to pump a quart at idle. If you are moving a quart or more you are probably O.K.
thanks, I'll try that. You're not an engineer, are you? Your pump terminology sounds like a man with experience...................thanks again, as always this forum is great!
 
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