"Frank" wrote in message
...
Tony Cox wrote:

Some models of 172 *require* you to select a single tank
above 5000', due (supposedly) to vapor lock problems.


No 'supposedly' about it. Ours locked at 7500' on a humid day because one
of
my partners didn't believe it could happen and didn't follow the
procedure.
Fortunately an airport was within glide range. Strangely enough, by the
time he landed the engine was running fine again....
--
Frank....H

Its happened to me too. I said 'supposedly' because I've not
heard a plausible explanation as to why selecting one
particular tank rather than both should affect the chance of
vapor lock. Is the fuel selector close to a heat source?

--
Dr. Tony Cox
Citrus Controls Inc.
e-mail:
http://CitrusControls.com/