REFLECTOR: Fuel pump cooling

Scott Derrick scott at tnstaafl.net
Tue Aug 28 20:20:34 CDT 2012


I've had this happen a few times this summer on flights longer than 2.5 
-3 hours.  Ran all winter with no problem so I think its heat related.

I typically run LOP, better mileage, lower temps,less pollution.

I can easily setup LOP when reaching my cruise altitude. I rarely have 
to re-adjust it after getting in the desired setting.

When its really hot, say 15C+ at 11500, after a couple hours the mixture 
seems to wander just a little bit and I have to periodically re-adjust 
to get it back.  We are talking less than 0.1 GPH change.

Once I get the engine really heat soaked after a few hours of 
flight(when the LOP starts to be work to maintain) and then stop for 
gas, take off climb to altitude, now its really hard to get it to run 
LOP?  It over  leans, then under leans.  If I then run it for awhile ROP 
and let things cool down from the climb, I can get it to run LOP but I 
still have that intermittent wandering mixture. Let the engine cool down 
over night, next morning LOP is easy again with a engine starting from 
cold.  I've had a few departures after it sat for a couple hours after 
landing and it leans easy then too. Only those hot fast turn arounds 
exacerbate the issue.

I noticed the T210 that uses this same engine has a cooling duct running 
to the fuel pup which is shrouded.  I don't have this. I'm thinking 
maybe it takes summer temps and a couple+ hours to get the fuel pump 
really hot enough to, I don't know, loose it mind?

The turbo setup on this version TIO520 is very sophisticated.  Once you 
set the throttle you can climb, descend and change prop rpm and the MAP 
doesn't move at all. Very easy to fly.  My fuel pump is from that 
original turbo setup.

Lycomings use an entirely different fuel pump so I don't think their 
setup would apply.

Any body else see this problem thats running LOP? Is your fuel pump 
cooled?  This is a 1986 vintage 520, with I think a similar fuel 
pump(carbon vane) is used on later models.

Scott

-- 
What the superior man seeks is in himself; what the small man seeks is 
in others.
Confucius


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