On Sat, 16 Dec 1995, Mark McCulley wrote:

> I'm curious how you used the pressure tester to diagnose the radiator.

The tester is screwed on in place of the pressure cap and then pumped up
to pressurize the system, with the engine stopped.  Then you start
looking for leaks and watching the pressure guage.  For very slow leaks, you
can leave it pumped up all day until enough coolant has leaked to be
visible. 

> It seems that the system would have to be up to temperature so that the 
> thermostat would be open, but then the system is under pressure anyway. I'm 
> assuming that you can only use this tool to apply pressure to the coolant 
> reservoir, or to test the pressure cap. Hmm, I guess you could remove the 
> thermostat and then pressurize the system while it's cold. 

The thermostat doesn't affect pressure testing because it only closes one
"loop" in the circuit without isolating any part of the system.  The
closed thermostat is not 100% effective as a valve anyway.  The tester
replaces the cap so it pressurizes the whole system just as the cap would. 

> How much pressure did you have to apply before the pinhole leaks became 
apparent? 

I pumped it up to 13-15 lbs. and left it overnight.  It took me three 
full-day trials before I found all the leaks.   These were really small 
holes.

Mike