I read on here and other places about “ high flow” water pumps and wonder if they are needed and why. Some old cars didn’t even have a pump, they depend on thermal action for flow. Cummins engine company experimented with a “low flow” cooling system where the hoses going to the radiator on big diesel trucks were the size of heater hoses. The theory was the water goes through the radiator slower and gets cooler, therefore cooling the engine better. They scrapped the program after a while, but it DID work. I built a large water cooled air compressor on the ranch that I power with 100 horsepower tractors and put a Ford pickup radiator up high. The thermal process keeps the compressor cool and the radiator feels hot, with NO pump. So my question is does it make real difference if you have a regular water pump ....or one that flows 20% more. It looks to me, that if the water is flowing it should be cooling. Maybe there are other opinions out there? Bones
No,actully the speed it moves is key most of the time,and that is done with pulley sizes. Many things are sold,more to sell it vs actully help,except in odd cases.
Impellers come in different designs and some flow better than others. The style that looks like a bent up piece on flat stock would be the least effective. Either way, it is the thermostat that controls the flow rate.
The heat rejection capacity of the radiator (or heat addition capacity of the engine) is affected by 2 things. The mass flow rate of the coolant, and the temperature difference of the coolant across the engine or radiator. The Thermodynamic Equation: Q = Cp * M * (T2 - T1). Cp is a constant, based on the thermodynamic properties of the working fluid (ethylene glycol, water, or some mixture there of). Now, Here is the dirty little secret. Q is also essentially a constant. The engine can only generate so much heat. Some will get rejected to the underhood air and more will go out the exhaust pipe, the rest will get transferred to the coolant and oil. This means that as the mass flow rate increases due to your new wiz-bang water pump, the temperature difference of the coolant across the motor (or radiator) has to drop, but the engine is still rejecting the same amount of heat energy to the coolant and the radiator is transferring that same amount of energy to the air. (Energy can neither be created or destroyed) In other words. Old Water Pump (10 gpm): Coolant Inlet Temp 170 degs, Coolant Outlet Temp 180. New Water Pump (20 gpm): Coolant Inlet Temp 175 degs, Coolant Outlet Temp 180. (Assuming the thermostat will allow the additional flow with out increasing the head pressure on the pump to the point that cavitation occurs.....)
I disagree. A better impeller will be more efficient, and move more coolant. Conversely the less effective impeller will actually use more HP because of its poor design.
Interesting , In your other words statement, Why is it that the inlet temp is higher with more coolant flow?
This is a topic that comes up repeatedly, usually during the hotter time of the year. We see plenty of arguments that slowing the rate down will provide more time for heat transfer across the radiator, resulting in lower engine temperature, but that is incorrect. A faster coolant flow rate will result in lower engine temperature, as explained here: http://www.enginebasics.com/Engine Basics Root Folder/Engine Cooling Pg3.html
The reason the engine outlet temp doesn't change is due to it being a function of radiator performance. The amount of heat rejected from the coolant to the air by the radiator is governed by the mass flow rate of the air (your fan's efficiency or lack there of) and the temperature difference between the coolant and the air. If the air properties are held constant (72 deg F, 2000 cfm for example), then the peak (engine outlet) coolant temp will also be the same despite changes to the water pump and the coolant flow rate. Think about it like this, if the ambient air temperature and flow is the same across the radiator for both pumps, your outlet temp from the engine (inlet to the rad) will remain constant, but the inlet to the motor (outlet from rad) will increase to get to that smaller temperature difference, because the coolant spends less time in either the engine or the rad to absorb or reject the heat energy that causes the coolant temp to rise or fall. Please note, This is an approximation as well. A higher coolant flow rate also increases the amount of turbulence with in the coolant flow, and the increased turbulence increases the heat transfer rate from the engine to the coolant. The increased flow will also result in increased head pressure across the pump. The increased pressure also has an effect on the Cp constant (heat transfer coefficient), again causing a small, but measurable increase in the heat transfer rate.
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