The fuel pumps are low on the firewall, right?

Just open the oil door when you stop.  The chimney effect will be pulling cool air over the pumps.

On Tuesday, August 22, 2017 2:05 AM, Todd Bartrim <flyrotary@lancaironline.net> wrote:

    With my improved ducting I seem to be able to withstand extensive ground running without overheating (but, It was only 21C today), however I've noticed that the temps really take a spike after shutdown. I measure coolant temps out of the engine, into the Laminova exchanger, into the engine and behind both left & right rad. What I've been seeing is the engine temps hottest exiting the engine, cooler going back in, while running as it should be.

   But immediately after shutdown with no airflow the temps at the left rad (closest to turbo) starts to climb. The controller for my EWP will continue to run pump for 5 minutes after shutdown, so the coolant seems to be absorbing this radiant heat as the temps into the Laminova and then into the engine begin to rise as well. The engine acts like a heat sink absorbing this heat  Kinda backwards I figure. But not a big deal, if I fire it up again or if I'm done for some time.

However when I went in for dinner and came back out an hour later I couldn't get enough fuel pressure to start (max 16psi). I converted to a returnless fuel system which seems great, however my hi-press fuel pumps are firewall mounted rather than in-tank as a true returnless system has. I do have low pressure Facet pumps supplying the system in a cool location, however this wasn't enough to overcome the vapor pressure. I opened the cowl oil hatch to vent the heat and an hour later I checked and all was good again.

  Previously I had a small NACA duct on the belly of the cowl feeding a 2" scat tube to cool the fuel system in flight as I had all that other hot air swirling around in there without proper exit ducting. That duct is still available as I only surface filled it with foam and then glassed over it, so I could chisel that out and use it again, but I don't think that will do much good as it would really only cool in flight and I don't think that is a problem.

   Sorry for the long-winded preface, but here comes the half baked idea.

Instead of going back to a return type system I was thinking about a push-button operated solenoid valve that would tee into the fuel line before the regulator and return fuel to a main tank only while the button is pushed. It would have to be mounted before the regulator so that it would be able to vent hot fuel when the pumps can't reach enough pressure to open the regulator. And because it would only open when the button is held there would be no worries about accidentally pumping fuel overboard through a vent from an already full tank.

  So the thought is that I fly to some airport, taxi in to get that $100 hamburger, back out an hour later, heat soak leaves me unable to get any fuel pressure so I hold that button in for a minute while my facet pumps move cool fuel into the system and hi-press pump starts doing it's hi-press thing, let go of the button and start as usual.

  So is this a lousy idea, a good idea, or is this already being done and I just missed the memo?

I welcome all comments & criticism on this. Once I haul this thing back to the airport I really don't want to be doing any more work to it. 

Todd Bartrim  --  Half baked is what I do best!