Re: Changing 165 fuel delivery

[Shannen Durphey <shannen@grolen.com>]

Garfield Willis wrote:

> 
> What's been the universal problem with those schemes is the fuel pump
> adds mechanical energy to the gas while it's recirculating it, and
> without the cooling from the larger main tank's surface area, the gas in
> the reservoir gradually heats up, vapor pressure drops, bubbles start to
> become visible in clear fuel lines, and before you know it, things start
> to go to shit.
> 
> Now, obviously Merc has this setup working for them, so I don't mean to
> say it's impossible (nothin like an "existence proof", eh?), but I
> mention our experiences in XA rather to suggest that they must be doing
> something quite right, to avoid the problems that have commonly plagued
> us in our applications. IOW, there may be dragons here.
> 
> Just me dos centavos, amigo.
> 
> Gar
> 
Well, since it's out here for discussion... : )
You raise a good point, one which I have thought about for a couple of
days.  You can add heat energy to the warning also, as marine engines
have t-stats rated as cool as 140 degrees, while autos of course will
run much higher (my temp gauge stays around 230 on the highway during
warm days).  

I have a small power steering cooler mounted in the return fuel line
of my 57 Chebbie pickup, to cool the fuel before it returns to the
tank.  The reason for this is to reduce vapor formation in the in-cab
mounted tank and the odors associated with it.  I dunno if this is an
option in an XA application, but it's not unreasonable for me.  And it
can be positioned to help cushion supply surges that can be caused by
fuel sloshing in the tank on corners or acceleration.  Old carby tanks
are often unbaffled, unlike the newbies that put them to service in an
efi system.

Questions for ya...  Altitude affects boiling point.  Do you think a
trouble XA system would perform better on the ground?  Have you heard
of any indication that this is a part of the complications?  Any
reports as to ambient temps in whatever part of the aircraft the
reservoir was mounted?
Shannen
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