"Roger Long" wrote in message
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[...]
It worked but running the engine full power (near sea level) while leaned
for best power and peak EGT with minimum airflow for the minute it took
seems pretty abusive to me. Maybe you can get away with it because the
CHT's have not yet risen to max.

Any thoughts? What were you taught?

As Dan says, there are other normal situations where you may run the engine
at higher power settings while stationary for extended periods of time. The
key is to pay attention to the engine gauges and make sure things don't get
too hot.

I do have a couple of personal experiences that may provide some insight
into the wisdom of this sort of thing, one in favor and one against. The
executive summary (for those who don't want to read the whole stories):

-- High-power runups may or may not cause engine temperature problems.
In my case, on a warm-not-hot (70 degree) day, I was able to do an extended
engine runup without any risk of exceed temperature limits

-- A rough mag may or may not actually be a case of plug fouling, and a
high-power runup may actually temporarily mask or otherwise "fix" a problem
that turns out not to be plug fouling but rather something more serious.

The long versions...

In the "in favor" category, I recently went up to the airport to introduce
our son to the airplane. As we've done with our dog in the past, the idea
was not to actually fly, but to taxi around and let him get used to the
experience gradually. As part of this, I also wanted to get the engine up
to temperature, as I hadn't had a chance to fly in several weeks (and didn't
have time to take a flight after taxiing around and unloading my
passengers). My goal was to see more than 180 degrees on the oil
temperature, while keeping the CHT below redline.

Keep in mind, also, that my airplane has a pusher prop, so even if on most
airplanes the prop might push a little air through the engine (though I
can't imagine this is a very noticeable effect, except for those planes
equipped with the "power-flo" prop and cowl), I don't get even this modest
effect to contribute to cooling.

Well, anyway...it turned out that taxiing around did nothing to raise the
engine temperatures to anything beyond the lower limits. Oil temps didn't
get much higher than 130-140 or so, and the CHT gauge stayed down at around
300 (which is the bottom of the green on that gauge). I stopped at a run-up
area during the taxiing and ran the engine up, but even after a couple of
minutes of this, I only barely got the oil temperature above 180 degrees,
while the CHT made it up to almost 400 (450 redline).

Interestingly, after the runup, once I started taxiing back, the oil
temperature crept up a little bit, maybe another 5 degrees or so, before
starting back down again. But at no time were the engine temperatures at
risk of exceeding their limits.

The moral of that story is that you may actually find it difficult to get
the engine temperatures too high. It will, of course, depend on outside air
temperature, and the nature of the engine's cooling system (my engine has
oil coolers), but I see nothing obviously wrong temperature-wise with doing
higher-power runups.

In the "argument against" category, I have a somewhat more disconcerting
experience. You may recall earlier this summer I had a very subtle but
troubling change in engine noise during takeoff, causing me to abort the
flight and return to the departure airport. As part of that story went, I
had my mechanic come by and inspect the airplane, and then we flew it over
to his airport with him along for the ride. Before taking off, we had a
rough mag, which we spent a few minutes with a high-power runup clearing.

When I posted that, someone suggested it would have been better to just shut
down the engine, pull the plug, and clean it by hand. At the time, I felt
that was a little impractical, since a) we had no shop handy where we could
pull the plug and clean it, and b) it seems like if you can clear the plug
with a runup, why not do that?

Well, in hindsight, I'm not sure we had a fouled plug, and if that had been
the case, we would have realized that when we pulled it. Where does this
hindsight come from?

Well, last Sunday when I went to go flying, during the runup I discovered a
rough mag again. I did the usual "increase power, lean engine" routine to
try to clear the plug. When I did the mag check again, I discovered that
mag was nearly dead. As soon as I switched to the mag, the engine stumbled,
and then died completely.

Oops. That's definitely NOT a fouled plug, unless by some incredible
coincidence, all six plugs fouled simultaneously and solidly (and I've never
heard of that happening).

So, what did it turn out to be? The p-lead wire, where it went into the
mag, had chafed against the ferrule that created the entrance into the mag.
The insulation on the wire had been cut all the way through, and now the
p-lead was shorting out against the magneto case! I had simply gotten to a
point where it had shorted out solidly enough to have an easily detectable
problem.

In hindsight, it's entirely possible that the shorting had already begun
back at the beginning of summer, and that it was responsible for the rough
mag check we had "cleared" before. Some extra vibration at the higher power
settings might have just moved the wire enough to provide normal operation,
at least briefly.

Had we pulled the plugs, we would have seen that they were not fouled after
all, and that would have suggested to us that we had a more serious ignition
problem somewhere else.

Now, it might still have been a pain to diagnose. I don't know. I also
don't know if it would have resulted in us not taking that flight (or all
the subsequent ones I made successfully since). But I seems like we would
have at least had a little more information to work with.

I don't know if any of the above information helps. But it should give you
food for thought, anyway.

Pete