I think it was an old 60ish Ford Falcon wagon with a 260 V8 it's been a
> > long
> > > time. Just thought that the water was going through the radiator so
fast
> > > that it didn't have time to transfer the heat.
> >
> -------------------------------
> This is a common misconception. You do not have to slow down the water.
> Faster is better for better cooling
>
> Bill Schertz
> KIS Cruiser #4045
My Falcon station wagon had a 144 cubic inch in line 6 cylinder. The Falcon
sprint had a 260 inch V-8. After that blew up, I installed a 283 Chevy. Not
difficult at all.
Stock American engines have pumps massively over sized in order to provide
sufficient coolant flow at idle in the Gobi desert. In general, all autos are
similar. The top radiator hose (pressure side) is small. In some cases 1 1/8"
ID. While the lower hose (suction side) is large in diameter and contains a
wire support to prevent collapse (pressure going below one bar) at high RPM.
A balance must be maintained between flow rate exiting the pump and suction
side pressure. It difficult to imagine that the rather incompressible coolant
could be in the same circuit and be at very diverse pressures. Coolant enters
the pump from the larger lower hose and is pressurized and forced through the
engine. Not much resistance there, so little flow rate is lost. Leaving the
engine the coolant passes through the thermostat. The thermostat is a small
diameter sharp edged hole in a sheet metal disc with a sharp edged poppet
valve hovering over it. Not at all conducive to flow, even when wide open at
operating temperature. The thermostat is always the restrictor in the coolant
system. Then into the small upper hose into the radiator. The radiators can
provide a wide range of resistance but generally less resistance than the
thermostat. Then the larger lower hose (low resistance) and back into the
pump. When the oversized pump is revved up, the thermostat restriction
increases coolant pressure inside the block. The thermostat limits flow rates
and decreases pump inlet demand. So long as the pump demand is limited there
is limited chance of cavitation.
Without restriction of the outlet side of the pump, the radiator becomes
the restriction, but nothing like a sufficient amount. Coolant flow rates
increase dramatically and keeping the suction side lower hose pressure above
one bar becomes difficult. Without the wire support installed, you will suck
it flat. Actually ambient air pressure will crush it, but it is the same
result, not matter how you say it.
So, high flow rates through the engine is good for total heat
transfer. High flow rates through the radiator(s) is good for total heat
transfer. High pump output requires high pump inlet flow that is at the end
of the restriction trail. The pump will begin cavitating if inlet flow is
insufficient. Cavitation can eat away the impeller blades and cause pressure
spikes in the coolant. This can dance clamped connections apart, and overcome
pressure relief caps and dump coolant.
So what to do? All of this has been covered here before but let me put it
together in one lump. You could slow the pump down. Bigger pump pulley or
smaller crank pulley. You could make the pump less efficient by reducing the
impeller diameter or reducing vane height. You could run a higher pressure
cap on a remote pressure recovery bottle to keep total system pressure
higher. The pressure you could run is only limited by radiator design. Around
22 pounds would be good. you could do all of these, or some of them. But
there is one thing you must do.
You get the Barlow out and carve into the barn wall this missive: I will
never run my system without a real live thermostat, or (if you fear
thermostats), a real live restrictor in place of a thermostat. Like a big
V-8, the Mazda pump is oversized a good deal, to perform at the usual 2,000
RPM or less most of them see. It is very effective at 6,500 RPM. On the race
car, all of the water leaving the block must pass through a 5/8" hole.
Ouch!!!. That is to maintain control of suction side demand at 9,400 RPM.
Still, the upper radiator hose is as solid as a piece bar stock at high RPM.
For 6,000 or 6,500 RPM 3/4" might be small enough. The added benefit of the
restrictor is the high coolant pressure inside the block. On the dyno we had
an MGB engine showing over 40 PSI at 7,500 RPM. That with a pump from the
stone age.
What is the boiling temperature of coolant at even 30 PSI? Next season I will
recover the coolant pressure on video tape and report it to you.
Lynn E. Hanover
We are about to get some flow data on the pump at 7500 RPM as Bill Schertz
hopefully received an 8 inch pulley for his table saw motor today.
Lynn, while you are at it please install another pressure gage
just before the pump. There is nothing like real world numbers.
Paul Lamar
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