To Lynn Hanover and all,
 >
 >          The "Stewart" web page mentioned above is the source I mentioned
 >  in a previous post concerning the advisability of placing the radiator
 >  pressure cap to the inlet side of the water pump. Would you review the
 >  "Stewart" tech info on this subject and give us your opinion?
 >
 >          Kelly Troyer

 Excellent advice. These guys obviously know what they are talking about.
 It makes good sense to put the cap after the radiator pressure drop.
 The inlet side of the pump is the lowest pressure point in the cooling
system.

 Paul Lamar

The pressure cap should not see any dynamic part of the cooling system. It is
a fuse to prevent the system pressure from getting high enough to blow a hose
off or swell the flat tubes in the radiator. A filler port mounted as high in
the system as possible is good. It need not be a pressure cap, just a
sealable port. Like a "B" nut cap on a dash 16 male fitting or similar. The
pressure cap need only be exposed to system pressure. Better to tap a
location where air tends to collect anyway. When the cap starts to dump
system pressure, better to be dumping trapped air first than coolant.
American cars are rigged with a recovery bottle that is not pressurized. The
radiator starts out full up and on startup starts to dump pressure as soon as
heat begins to build up, because the system is in hydraulic lock. It works
just fine. It is cheap. It is easy to understand. It has one little problem.
It won't return and lost coolant until
the engine is nearly cool, and the system pressure drops below ambient.
Many foreign cars use a pressure recovery bottle. The system pressure is
available to the bottle all of the time. The line to the bottle is run from a
high spot in the system (where air would collect). The pressure cap (fuse) is
on the recovery bottle.
The system is full and the bottle is about 1/4 full of coolant. As the system
builds up heat and pressure the air in the bottle is compressed to the value
of the cap. The
cap then vents only air to maintain the cap rated pressure. So coolant builds
up the level in the bottle to about 1/2 and the air above it is at 22 pounds
or whatever. If the coolant looses temp and volume, the system pressure drops
and the compressed air in the bottle drives coolant back into the system.
This is how the RX-2 and-3 systems worked. It was not as cheap but it works
better. I added a shrader valve to the bottle so I can have cap rated
pressure before I start the engine. Its been working since 1973. I do run a
restrictor in the water outlet to the radiator. I don't do the cuts around
the spark plugs in the housing. I have seen housings cracked through the
spark plug hole but I have not had it happen to me (yet). I noticed one day
the a friends MGB (think 1947 tractor motor) on the dyno was producing over
45 PSI of water pressure in the block. The upper radiator hose was as hard as
a rock. I voted for a restrictor to calm the load on the radiator and hose,
but it was not mine to change. But again I run on..........

Lynn E. Hanover

 
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