Lotus Elan

Aux water pump (Brain Fart)

PostPost by: holywood3645 » Mon May 08, 2017 6:08 pm

I needed a heater aux pump for a non lotus car and purchased this one (pic attached)
It has occurred to me that this could be adapted and used on a Twin Cam engine. I'm not considering replacing the original pump, but considering how I could use the pump to increase flow during stop an go traffic (I'm in so cal)
I have an electric fan that works, but I think the main reason for temps spiking in slow or stopped traffic is poor flow at low RPM.
I'm throwing this out for discussion. It could be a cheap fix if it would work, all I'm trying to do is increase flow through engine at low rpm while in very slow traffic
Has anyone played with this idea,

The pump is an $80 item.

James
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Last edited by holywood3645 on Mon May 08, 2017 10:51 pm, edited 2 times in total.
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PostPost by: TomR » Mon May 08, 2017 7:54 pm

This can be tricky. Pumps drive a volume of flow across a pressure difference, while pushing flow through the system requires a pressure difference. At any given engine speed, a centrifugal pump like the OEM pump will provide the specific amount of flow that results in the pump pressure lift and the cooling system pressure loss to be in perfect balance. You could conceivably put another pump in parallel with the OEM pump. However, as the new pump tries to drive more flow through the cooling system the delta pressure will increase and the flow through the OEM pump will decrease. Depending on the flow/delta pressure characteristics of both pumps you might get some additional flow, but it may be much less than you would expect from simply adding the flows of the two pumps together. Also, you could get backflow through either of them at low or high flow so check valves on both pump outlets before you join them together might be needed to avoid reducing flow at some conditions.

In any circumstances it would be very risky to put them in series. The new pump would almost certainly restrict the normal OEM pump flow if you put it on the OEM pump outlet side or cause cavitation of the OEM pump if you put it on the suction side.

Good luck. Tom
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PostPost by: holywood3645 » Mon May 08, 2017 11:43 pm

Thanks, Tom
My idea was to place the pump in parallel with the existing OEM pump, and discharge it into the twin cam engine some point upstream of the OEM pump. Drawing coolant from a point on the bottom of rad.

I would assume the discharge aux pump would take the path of lease resistance, joining the discharge of the OEM pump and flow through the engine and back in to radiator inlet. I would be looking for a point in the cooling system the I could possibly plumb the discharge of Aux into.

The basic idea is to increase coolant through the engine, only in low speed. The control could be auto or manual.

Thanks
James
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PostPost by: TomR » Tue May 09, 2017 1:11 am

What I spelled out is fundamental design of a parallel pump system, and everything I said in the first paragraph applies to your intended configuration. Unless you know the characteristic flow/DP curves of the two pumps and design the system properly you will not get the desired result. You might find the path of least resistance is backwards through your OEM pump or vice versa. Tom
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PostPost by: Gray » Fri May 12, 2017 12:06 pm

Pumps in parallel do not work as most expect, non return valves may also be required to prevent flows going the wrong way. I recall Lotus did recommend somewhere running the engine at higher revs to improve flow and hence cooling if stuck in traffic.
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