Again... to repeat a previous poster.. you really do NOT want stagnant water when the ambient is well below freezing. If you are going to play with this (turning off flow to one of your parralel radiators) then you need to know what the freeze point is for your "antifreeze" (a better term would be coolant). The term "antifreeze" is a misnomer. You get cold enough and it WILL freeze. The Prestone bottle in the garage that I have says its FP is -34 F for a 50-50 mix. I've had 50 degree ambient temps at 10k feet in July in Texas. I wouldnt want to think what the temp would be up north in January (if its even flyable..).
 
Keep SOME flow.
 
Dave

Russell Duffy wrote:

3) a 'weep hole' in a flapper valve that will allow a minimum amount of
flow to keep the water liquid?

 

I assumed having enough antifreeze to handle the cold, but I still don't like the idea of having no flow for any period of time if the primary pump quits.  I thought also about having a high/low switch, so that there's still some flow rather than just being off.  Then of course I realized that it would be better to just use one of controllers that Davies Craig sells, and be done with it.  I bet you could run that on one of the pump/evap core combos, and leave the other pump on all the time.  

 

Maybe I can get around to testing mine today.

 

Cheers,

Rusty (now officially using red)