Why is it bad to run the engine without flying?

From what I read and what people - whose opinions I greatly admire - tell me, it's bad to start the engine, run it for a few minutes (5-10), even at 1000 or 1200rpm, and then shut it down...just to circulate some oil and do a small bit of charging on the battery.

I'm not aware of all the reasons why this is a bad idea (just some) and I'd appreciate an education.

Thanks!

Broken in, or not? Two different situations. For the broken in engine, as long as you didn't get CHTs too high, what's the harm? Get the oil up close to normal temp, cycle the prop a time or two (if CS). Heck of a lot better than letting condensation and acid collect in the engine over time. Just be careful running it on the ground.

Low Pass:

Well broken in.

And yes I should have said run long enough to:

get CHT's and EGT's into the green
get oil temp into the green.

I have always heard that it is because a short run will not get the oil hot enough to eliminate any water condensation that results from combustion so you can end up with water in oil rusting internal engine parts.

Dragonfly:

That's the reason I heard...I'm wondering if there are any more.

thanks!

I don't think you don't want to run it just for a few minutes. One of the byproducts of combustion is water. Lycoming states you should run an engine at least 45 mins and get the oil temp up to 180 deg minimum to boil that water off.

As for running on the ground it's all about temp management. The cowling and baffling isn't designed to provide adequate cooling on the ground.

Also I doubt running the engine a few minutes will really put much of a charge the battery and probably won't even replace the capacity used up in the start.

Bottom line is I think it's OK occasionally I just wouldn't make it a habit as I think the cons out weigh the pros.

In a DVD that came with my Lycoming engine, the narrator states that about 1300 rpm results in the best ground cooling.

Of course, cowling-off runs should be kept brief (unless you have a plenum setup) because the rear cylinders won't have adequate cooling.

Air cooling systems on aircraft are designed for "in flight" cooling. Not running on the ground. Running on the ground does not give equal cooling for the cylinders. If you run the engine long enough for the oil to get hot, the cylinders will get inadequate cooling differential.
If you run for a shorter time, you will get condensation in the oil.

Bottom line, if you can't fly it, leave it alone.

As mentioned its pretty much just a water issue. Realize that aircooled motors are really sloppy piston ring to wall vs a water cooled so youre gonna be putting more water vapor in the oil than you might think. And it takes a fair amount of time for that water to boil off and make it overboard. How much time? Who knows. But the engine mfgs probably do have the best handle on it. Pickle the motor or fly, and as little as possible in between IMHO.

The issue is long delays between flights in the Winter

Thanks to all.

It seems that water vapor is the main issue, which makes sense.

I'm mostly thinking about Winter times (as I sat here yesterday at -33 with the wind chill). During Spring, Summer and Fall I can fly 2-3 times a week no problem. That keeps the battery charged and the oil circulated. It's only the Winter where I might have longer delays between flights.

Early in January I hadn't flown for 2 1/2 weeks. When I tried to start the engine to taxi over to the hangar in which my annual was going to be done, the prop turned almost one rev and stopped. The battery was gone.

Prior to that attempt I had not gone a week without flying prior to the annual. The engine started just fine every time.

The battery is a Gill G-25 flooded battery. I do not know the age of the battery.

So I pushed the plane over to the hangar and recharged the battery and when the annual was done, the plane started up just fine.

So I'm thinking about long delays between flights in the Winter on the order of 2-3 weeks. I saw two issues:

1) corrosion in the engine

2) Battery life (due to the above non-start).

To help with #1 I added Camguard.

To help with #2, I just bought an Odyssey PC925MJ AGM battery, along with an Odyssey charger. That battery is supposed to have more cranking power and be able to last longer between charges - especially at low temps. The MJ is also supposed to help with that at low temps.

Also, as I fly acro it's better to have an AGM than a flooded battery.

I'm hoping these two things will alleviate the worry I have about going 2-3 weeks without flying in the Winter time.

The only other Winter aspect I have to deal with is engine pre-heat and I have the Reiff Turbo cylinder heaters and oil sump heater on hand ready to install. That plus a smartphone switch and I think I'll have Winter under control. Just in time for the end of Winter

Any other thoughts along these lines are welcome.

Thanks!

You shouldn't see corrosion inside the engine in 2-3 weeks. You shouldn't have a dead battery in 2-3 weeks.
It is "generally" accepted that flying once a month should keep things healthy.

Corrosion occurs the instant water and acid condense in the engine on unprotected surfaces. It's damage is continual and progressive. Generally, water is present in engines in two forms. Dissolved in the oil and condensing as liquid water on the exposed surfaces inside the engine.

Regarding oil dissolved in the oil, heating the oil increases the amount of water than can be dissolved into the oil. Heating the engine parts by running running or with external heat source drives out the liquid moisture and stops/prevent condensation (while warmer than dewpoint).

As for running on the ground being different than in the air, yes - when needing to remove large amounts of heat (high power), it won't work. Can't remove enough heat to control temps. But watching each CHT individually will allow you to see each cylinder and prevent one from overtemping. And these are air cooled engines relatively tolerant of temperature extremes. Like flying through rain and taking off on a 110-F day.

As for heat distribution, it will be better on the ground, to a point. Heat will be conducted quickly and more uniformly through the cylinder assembly with lower cooling air flow. Kind of like warming up and running up before takeoff.

What's the point? To distribute lube oil to the internal components and drive out the water from within the engine in order to decrease corrosion. Best option? Add a heater or condition the space where the engine is located to prevent the moisture from condensing and to keep the relative humidity low. Second best, circulate the oil and raise the temperature of the engine to a point where the majority of water will flash. And you don't have to be at 212 F for water to evaporate.

Saville said:

Thanks to all.

It seems that water vapor is the main issue, which makes sense.

I'm mostly thinking about Winter times (as I sat here yesterday at -33 with the wind chill). During Spring, Summer and Fall I can fly 2-3 times a week no problem. That keeps the battery charged and the oil circulated. It's only the Winter where I might have longer delays between flights.

Early in January I hadn't flown for 2 1/2 weeks. When I tried to start the engine to taxi over to the hangar in which my annual was going to be done, the prop turned almost one rev and stopped. The battery was gone.


The battery is a Gill G-25 flooded battery. I do not know the age of the battery.

Any other thoughts along these lines are welcome.

Thanks!

Click to expand...

I've never had good luck with Gill batteries. I have the Concorde on my archer and it's worked fine. During the winter I fly every 2 weeks, sometimes longer depending on conditions at the airport.

I take my battery out and keep it at home. Doesn't take very long to remove and reinstall it and I think it will last longer... Not to mention I usually trickle charge it the day before I head to the airport.

are you pre-heating prior to starting in the winter? If you are not then that's really bad. The oil can't circulate and the smaller bearing clearances don't allow for oil to protect the journals as well. Also it is a much bigger starter load on a cold battery. Most engine wear occurs on cold startups.

sblack said:

are you pre-heating prior to starting in the winter? If you are not then that's really bad. The oil can't circulate and the smaller bearing clearances don't allow for oil to protect the journals as well. Also it is a much bigger starter load on a cold battery. Most engine wear occurs on cold startups.

Click to expand...

Yes I'm pre-heating but I'm borrowing one form an FBO or using a much slower heater. I don't want to borrow from the FBO so I got the Reiff system.

With respect to batteries, I'm currently wondering what I'll do with the 9-month-old Gill battery I removed from my friend's certificated aircraft when it would no longer crank the engine. The Concorde RG25XC that I installed in its place cranks the engine with vigor. So much so that when I first hit the starter button when the Concorde was installed, the starter engaged with such a clang that I thought I had broken the starter. The Gill battery had NEVER cranked like that. Needless to say, the Gill that's sitting on my basement floor is, I hope, the last Gill that I'll ever buy. J U N Q U E! (But it's certified! LoL)

Ground running?

Nothing seen here convinces me that ground runs are bad if: 1) you have full engine monitoring to assure temps are fine in all cylinders and 2) you have external heat applied when engine is inop. We have operated 3 aircraft with Tanis or Reiff heaters through one or more overhaul cycles. All have done very well. Concerns have been voiced about leaving heat on full-time. A few years ago Aviation Consumer ran tests which showed no negative effects of keeping these heaters in full-time use - an attempt at getting hard data. Unfortunately most information on the subject is anecdotal. Also individual aircraft have widely variable ground cooling, so generalizations do not always apply. Show us the data, as Dan says. Something to think about - the engine manufacturers run their engines in a test cell before delivery (I'm sure they pay attention to cooling) and engine builders like Lycon offer variable test cell times (more time more money) to ease conflicts between break-in requirements and operational requirements for a brand new aircraft. Would love to hear more data bearing on this if anyone knows and will share. Thanks.

Test cells are designed for proper cooling of the engine in that particular environment.
An aircraft cooling system is designed for proper cooling in flight. While you can monitor cylinder differential cooling on the ground, you cannot control it.
I've been building and wrenching on Lycomings for over 40 years and will continue to run them on the ground only when necessary and with a proper cooling set-up.
You are free to do as you want.

Let's ask Lyc?

this is not 'hard' data, but the last thing I read in a Lyc manual was....."don't ground run" thinking it's 'good' for the engine.

http://www.lycoming.com/lycoming/support/TechnicalPublications/ServiceLetters.aspx

see SL 180B Engine Preservation for Active and Stored Aircraft

but even they change their tune. For the first 40 years, they said it was ok to pull thru a dormant engine. Then they changed that to say 'don't'.
The important things you'd like to coat with oil, are 'splash' lubricated, and that ain't happening until the oil is warm and at a decent rpm.

all this from my sometimes faulty memory, but fairly sure it's 87% correct,
8 times out of 10.

The engine manufacturers that we use do not recommend ground run on the engines just because we can.

If you want to run it on the ground just because you can, please go look at the manufacturers recommendations and show me where it says to run it on the ground other than for checkout before 1st flight after a rebuild.

We have already had one person that has been working on these engines for 40-years say not to run it. Please look for someone with 40-years or more experience say you can. 40 people with one year experience with these engines is not the same as one with 40-years of experience.

Lycoming Tech Tips can be download here.
One can find Lycoming recommendations in the Tech Tips document. Do a search for ground and read.

See page 62.
From page 62 follows:
Some operators are running the engines on the ground in an
attempt to prevent rust between infrequent
flights. This may harm
rather than help the engine if the oil temperature is not brought up to
approximately 165˚ F, because water and acids from combustion will
accumulate
in the engine oil. The one best way to get oil temperature
to 165˚ F is to fly the aircraft. During flight, the oil normally gets hot
enough to vaporize the water and most acids and eliminate them from
the oil. If the engine is merely ground run, the water accumulated in
the oil will gradually turn to acid, which is also undesirable. Prolonged
ground running in an attempt to bring oil temperature up is not
recommended because of inadequate cooling that may result in hot
spots in the cylinders, baked and deteriorated ignition harness and
brittle oil seals which cause oil leaks. Pulling on engine through by
hand if it has not been run for a week or more is NOT recommended,
and can result in increased wear. Refer to Lycoming Service Letter
L180.



Just my opinion.

Canadian_JOY said:

With respect to batteries, I'm currently wondering what I'll do with the 9-month-old Gill battery I removed from my friend's certificated aircraft when it would no longer crank the engine. The Concorde RG25XC that I installed in its place cranks the engine with vigor. So much so that when I first hit the starter button when the Concorde was installed, the starter engaged with such a clang that I thought I had broken the starter. The Gill battery had NEVER cranked like that. Needless to say, the Gill that's sitting on my basement floor is, I hope, the last Gill that I'll ever buy. J U N Q U E! (But it's certified! LoL)

Click to expand...

We had the Concorde in our -10 for 10 years with the lower torque Skytec starter. We always had the bump-to-start issue. We out in an Odyssey PC925 and it cranks with so much more vigor that we aren't going to change out the starter.