From: "Bill Bradburry" <flyrotary@lancaironline.net>
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To: "'Rotary motors in aircraft'" <flyrotary@lancaironline.net>
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Subject: Radiator Cap
Date: Tue, 01 Jul 2014 16:55:14 -0500
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Well, not much activity in the last couple of weeks!?

So when I designed my cooling system I installed a fire extinguisher bottle
that I had welded a radiator neck onto.  I put a 21 pound radiator cap on
this bottle.  I keep the bottle about 3/4 full of coolant.  If there should
be an overflow of this bottle and the pressure is exceeded, the coolant
would flow overboard.  AFAIK this has never happened. My coolant pressure
runs around 20 pounds in flight, so I assume that the radiator cap is
burping air to keep the pressure at that level. 
I have a tube from the bottom of this fire extinguisher that goes to the
overflow tube in the radiator neck of the radiator.  This radiator neck has
a radiator cap that has no pressure control under it.  This radiator cap
only seals at the top and does not block off the lower seal that is present
in the radiator neck.  I take my coolant pressure from this tube that goes
between the radiator neck and the bottom of the coolant bottle

Recently after I shut the engine off, I noticed that I was loosing coolant
from the area of the radiator cap on the radiator.  The radiator cap is
probably 7-8 years old but I only have about 130 hours running the engine,
100 of which is in flight.  I assumed that the radiator cap was leaking and
so I decided to replace it.
  
Easy said not so easy done!

I have looked high and low for a radiator cap that does not have the spring
loaded pressure regulator under it.  Most auto parts guys just say HUH?

I didn't write down any part numbers when I bought it and don't even really
know where I got the damn thing.

Does anyone have a similar system and or know where I can get a replacement
radiator cap?

I have considered getting a regular cap and drilling a bunch of holes in the
lower seal but I would prefer not to do that if possible.

Thanks for any help!

Bill B