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Old 08-04-2014, 04:26 PM   #11
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Location: Chessington, Surrey
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Make: Vauxhall
ECU: Motronic 2.5 - Group N Chip

Originally Posted by MiniLandy View Post
The volume of water moved through the engine isn't going to change just because the overall volume has increased, surely?

The engine doesn't care how big the total volume of coolant is, it just cares that the coolant volume passing through it is sufficient to absorb enough heat from the engine. You could stick the inlet and outlet hoses of the coolant system into a couple of swimming pools if you like, I can't see how it would put more strain on the pump.
Just doesn't work like that. Otherwise what your saying is that we could just use an "A" series water pump on a Chevrolet V8 and expect it to cope with a larger volume of coolant and bigger circuit / bigger radiator, more bends etc etc and still get the job done.

Mechanical automotive water pumps are centrifugal. The impeller has been sized to the coolant circuit when the engine and cooling system were designed. The designer will have calculated the flow rate and the amount of coolant that the pump needs to circulate in a given time to adequately cool the engine under all operating conditions. If it's just a little bit more piping then OK the pump may cope, but be less efficient. If we are now taking about having an engine in the back and pipework up to a front mounted radiator and then all the way back to the engine again, that's a lot bigger a system.

If the pump was electrical then you can increase the pump speed independent of engine rpm ( like davies craig), but the cars mechanical pump is driven off the cambelt or waterpump belt, so only pumps more when rpm increases. At idle these pumps are highly inefficient. At higher speeds they sap lots of horsepower.
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