Hi Bob;

    Sorry I didn't get back to you sooner, but I've been tied up these
last few days dealing with lawyers as we are finalizing a land purchase,
along with a few other personal commitments (hockey, kids swimming
lessons, etc...). This thread seems to have run it's course already but
I'll add in what I can.

    First OAT. While it does get extremely cold here by most of your
standards, winter doesn't last forever and we do get some pretty hot
summers occasionally seeing temps as high as mid 30'sC. I realize this
still falls short of some of your temps. I don't always log OAT on every
flight but some of my test flights I did log this, however I'm at work
and that info isn't. I do recall at least one of those flights last
summer was at 31C. Unfortunately I painted my wing leading edges dark
blue, so on a sunny day my fuel temps will often be close to 40C, before
I even get started. I've seen them get as high as 45C during taxi and
run-up, with no problems. As soon as I get airborne with flow through
the cooler, fuel temps immediately begin to drop.
The cooler you've found looks great. I'd have bought that if I'd
found it before, however I'm satisfied with the one I made.
This nonsense that it won't work is very subjective. I've proven
that it does work for me, however this is really no different than the
issue with header/sump tanks. Ed is flying quite happily and
successfully with his, while I was never satisfied with mine. This is
probably due to the tendency of builders to not exactly duplicate a
successful system due to differences in airframe configuration or
required mission. Tracy on the other hand is quite satisfied with his
arrangement and apparently it has been copied by several others who are
also quite happy with it. I know I wouldn't be satisfied with that
arrangement, but that is why I like the experimental category, as we are
free to build and experiment as we desire.
If you want to go with this system then go for it, but beware
that variations in your airframe configuration and flight profile could
have varying effects. No guarantees from me :-)
If you do have an existing 1/4" return line, I would expect that
it should suffice as long as you still have an additional vent line from
the tanks and are not just "T" into the tank vent line to return.
I should point out that while it has been mentioned that since
the outlet of the pumps is often less than the ID of the fuel line this
is your limiting factor in flow. This isn't really the case. A small
restriction such as this creates a pressure drop through the "vena
contracta", but much of this pressure is recovered downstream. If anyone
actually cares about this I can pass along the formula for calculation
of the permanent pressure drop through an orifice. This means that a
1/4" line with a 3/16" restriction at some point will not have the same
lower flow as a 3/16" line, but will still be slightly less than a 1/4"
line with no restriction.