Hot Starting Fuel Injected Engines

"Corky Scott" wrote in message
...
With my last experience, the engine actually went into hydraulic lock
without me touching the controls or using the auxiliary fuel pump.
The prop barely turn half a turn before it stopped and the starter
couldn't crank it anymore.

I'm not sure what exactly is going on here, but I don't think it's
"hydraulic lock". As a previous post hinted at, "hydraulic lock" is
something that is specific to only certain kinds of engines (like radials)
and not those found in C172's. It happens when oil drains into the
cylinder, putting an incompressible substance into a space that wants to
compress when the engine turns.

If you are having trouble with the starter not being able to turn the engine
on a C172, you've either got a dead battery, or something worse is going on.

When you first wrote "hydraulic lock", I actually assumed you meant "vapor
lock", which is what happens when the fuel in the fuel lines is heated to
the point of vaporization, preventing it from being pumped to the engine.
This is the usual problem when starting hot engines, especially fuel
injected ones (carbureted engines usually have enough fuel in the float bowl
to let things get sorted out during engine start, so even a little vapor in
the fuel lines won't cause a problem with starting).

But now it sounds like you did actually mean something other than "vapor
lock". I'm not sure what it was, but I'm pretty certain that, given that
you're talking about a C172, it wasn't "hydraulic lock". Even if hydraulic
lock were possible on a C172, it wouldn't be related to a hot engine start.

There are actually two fuel pumps, one works with the engine turning,
the other is the electric auxiliary pump. So fuel will be pumped to
the injectors the moment the engine starts turning.

I'm not familiar with the new fuel-injected C172's, but it's entirely
possible that with the electric fuel pump running, fuel will be pumped to
the injectors and even into the engine the moment the fuel pump is turned
on, regardless of whether the engine is turning or not. That's how the
fuel-injection system for the Lycoming 540 engine in my plane works.

Pete