Water in our oil, or just alot of hot air?

wrote in message
oups.com...

Drew Dalgleish wrote:
Running an engine on the ground is bad. It's boring and wastes gas
just go do some circuits to get the oil warm.

What proof is there that it is bad? And sometimes weather and
circumstances don't allow people to fly. I believe that ground running
is better than bare metal corroding. My engine would have been corroded
a long time ago if the oil from a ground run would do that, and it
hasn't been.

Blue skies,
Rusty


One of the things we (at an auto company) have to do is make sure that cars
cold start well. And, nowadays, we even have to meet emission regulations at
lower temperatures. Now, the problem is that it's hard to get a lot of cold
starts into a short period of time. So, what to do? One technique is to use
cold fluids (water, oil, even air) to force cool an engine and get multiple
cold starts per day. When some dynomometers were set up to do cold start
after cold start, we started to grenade the engines in short order - largely
due to oil dilution from gasoline - you get some in the crank case with
every start and if you don't warm up, it builds up. Moisture from blowby
builds up too. Repeated short starts are, in general, not a good thing. What
you propose isn't nearly as severe, but short, repeated runs are not likely
to get you to the maximum TBO.

There's nothing magic about 180 degrees - but the warmer it is, the higher
the vapor pressure from the water, and the more it dries out. Aircraft
engines are at a bit of a disadvantage since they still just use a breather
tube so the only "air" going into the crankcase is from the blowby which is
loaded with water and CO2 (all engines have blowby - it's just a question of
how much). The positive flow from the PCV system on cars has been shown to
increase the longevity of the engines, but just sticking one on an aircraft
engine won't have the same benifit since aircraft run at high manifold
pressures (little or no vacuum) for extended times so you wouldn't get much
flow from a PCV so all you can do is warm it up enough and run it long
enough for things to dry out.

Oil needs to be changed because the long chain hydrocarbons break down and
viscosity changes. Also, there are a lot of additives for friction and wear
reduction, foam supression, etc. that tend to break down. Carbon particles
are not a problem for gasoline engines since there is almost no soot
generated. Diesel's on the other hand, make lots of soot, and some of it
makes it's way into the oil.

If you really want to circulate some oil, crank without starting . If you
want to run it, run it long enough to warm up. Short runs aren't an instant
disaster, but they really aren't what you want to do for a long TBO.

But, it's your engine...

--
Geoff
The Sea Hawk at Wow Way d0t Com
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When immigration is outlawed, only outlaws will immigrate.

Good Post, Captain!