AVGAS used to flush crankcase at oil change?

[Bill_Pyles]

I read somewhere that avgas can be used to flush the crankcase after the old oil is drained and prior to filling the crankcase with fresh oil.  A gallon of avgas is allowed to sit for a few minutes in the crankcase in order to thin the residual oil and to keep it from contaminating the fresh oil.  What is the general consensus about this practice?  Are there any good reasons not to flush with avgas?  Is there a better alternative fluid?

[pjsny78]

I have never heard of this practice but would NEVER do this. no one can convince me that putting AVGAS in a crankcase is a good idea.

[DaV8or]

Jose should be along soon. I believe he does this.

[stevesm20b]

I think it would be much better to just drain the oil after a flight when the oil is still hot. 

[jetdriven]

I used to fly an old 310 that has an avgas oil dilution system installed.   It thinned the oil in cold weather. 

 

[N601RX]

I have not done this before, but I don't think anyone is filling the crankcase with avgas.  They are putting a gallon or so through the oil fill tube which goes straight to the sump.  The thought is that it would disolve and flush any sludge that has accumulated in the bottom of the sump. If someone is going to do this then they should remove the screen and let it flush out the oil passage that goes the screen.  Otherwise you may just was wash something down into the oil passage that goes to the screen.

[johnggreen]

I have used this procedure in small engines, like lawn mowers, that do not have oil pumps to "stir" the oil.  Small engines that rely completely on splash from the crank seem to build up sludge more in the sumps than larger engines with oil pumps.  As to whether it is any value in a horozontally opposed air cooled engine or not, a rebuild mechanic could probably give an "educated" guess.

As to whether there is some danger from the fuel in the crankcase.  I do have an educated opinion.  If you do it, it might wash oil from some bearings so, if you do, change the oil and run the engine immediately to reoil all bearings so that no rust can start.

A small amount of fule mixed in the oil will not matter.  It will burn out almost instantly.  In World War II radial engines, a fuel/oil mixer was standard equipment.  I owned an AT-6, the first flying airplane I bought after law school, that had the system.  In cold weather, before you shut down, you turned a valve and let fuel flow into the oil reservoir to increase the viscosity of the oil for the next start up.  Otherwise, the 60 weight oil just wouldn't let the engine turn over if it was below freezing.  The fuel burned out as the engine warmed and everything went back to normal for flight.

That AT-6 also had an inertia starter that had to be the coolest thing I ever owned.  The sound of that starter spinning up then the cough of that radial engine and the belching smoke was just next to sex as a thrill.  You couldn't fire up that enigne without grinning from ear to ear.

And you poor souls think a Mooney is cool!!!

Jgreen

[PTK]

Quote: Bill_Pyles

I read somewhere that avgas can be used to flush the crankcase after the old oil is drained and prior to filling the crankcase with fresh oil.  A gallon of avgas is allowed to sit for a few minutes in the crankcase in order to thin the residual oil and to keep it from contaminating the fresh oil.  What is the general consensus about this practice?  Are there any good reasons not to flush with avgas?  Is there a better alternative fluid?

[Bill_Pyles]

Just to be clear, I am suggesting draining the oil, closing the drain valve, pouring a gallon of avgas in the oil filler pipe--(same place oil is added), let the avgas sit for 15 minutes, then drain the avgas/residual-oil until it stops dripping and then close the valve, install a new filter and pour 8 qts of new oil in.  I can't imagine there would be enough avgas left in the sump to cause any issues.  I also don't believe avgas will corrode bearings!  If I do this, I will measure the gallon of avgas and measure how much gas/oil drains out after 15 minutes.  I am just looking to get as much of the old oil out as possible.  Guess I will call Lycoming as well.

[PTK]

Be sure to change filter and clean screen each time as well. You'd be surprised how many people don't change the filter each time they change oil. Also you'd be more surprised how many AP's don't bother removing and cleaning the screen either. I had an AP one time get nasty with me when I questioned him about cleaning the screen. He swore up and down that my engine had no screen!! I made him take the cowl off and remove and clean the screen if he wanted to get paid!

[1964-M20E]

The finger screen at least on my plane is a real PIA (pain in the ass) to get to.

I cannot see why doing this would have any negative effects.

[N601RX]

Quote: Bill_Pyles

Just to be clear, I am suggesting draining the oil, closing the drain valve, pouring a gallon of avgas in the oil filler pipe--(same place oil is added), let the avgas sit for 15 minutes, then drain the avgas/residual-oil until it stops dripping and then close the valve, install a new filter and pour 8 qts of new oil in.  I can't imagine there would be enough avgas left in the sump to cause any issues.  I also don't believe avgas will corrode bearings!  If I do this, I will measure the gallon of avgas and measure how much gas/oil drains out after 15 minutes.  I am just looking to get as much of the old oil out as possible.  Guess I will call Lycoming as well.

[danb35]

I can't really see any negative effects to this, but I don't see much (if any) upside either.  The concern about corrosion, I think, isn't that the avgas itself will corrode the bearings, but that it could wash away oil which would allow them to corrode.  Easy answer to that is to run the engine once you change the oil.

If you change the oil warm, I'd also expect you'd get the vast majority of the old oil out--I don't think you'd get an appreciable amount extra by just pouring avgas into the sump, letting it sit, then draining it.  You would get extra oil out by running it with the avgas in the sump, but that seems like a bad idea on many levels.  I've known some folks who have done that (on cars) with diesel fuel, which at least has some lubricating properties, but even that seems quite risky.

[scottfromiowa]

Quote: johnggreen

I have used this procedure in small engines, like lawn mowers, that do not have oil pumps to "stir" the oil.  Small engines that rely completely on splash from the crank seem to build up sludge more in the sumps than larger engines with oil pumps.  As to whether it is any value in a horozontally opposed air cooled engine or not, a rebuild mechanic could probably give an "educated" guess.

As to whether there is some danger from the fuel in the crankcase.  I do have an educated opinion.  If you do it, it might wash oil from some bearings so, if you do, change the oil and run the engine immediately to reoil all bearings so that no rust can start.

A small amount of fule mixed in the oil will not matter.  It will burn out almost instantly.  In World War II radial engines, a fuel/oil mixer was standard equipment.  I owned an AT-6, the first flying airplane I bought after law school, that had the system.  In cold weather, before you shut down, you turned a valve and let fuel flow into the oil reservoir to increase the viscosity of the oil for the next start up.  Otherwise, the 60 weight oil just wouldn't let the engine turn over if it was below freezing.  The fuel burned out as the engine warmed and everything went back to normal for flight.

That AT-6 also had an inertia starter that had to be the coolest thing I ever owned.  The sound of that starter spinning up then the cough of that radial engine and the belching smoke was just next to sex as a thrill.  You couldn't fire up that enigne without grinning from ear to ear.

And you poor souls think a Mooney is cool!!!

Jgreen

[aviatoreb]

Quote: Bill_Pyles

I read somewhere that avgas can be used to flush the crankcase after the old oil is drained and prior to filling the crankcase with fresh oil.  A gallon of avgas is allowed to sit for a few minutes in the crankcase in order to thin the residual oil and to keep it from contaminating the fresh oil.  What is the general consensus about this practice?  Are there any good reasons not to flush with avgas?  Is there a better alternative fluid?

[Bill_Pyles]

Well, lead is also a lubricant and I am only talking $6 worth of avgas.  Moreover, some mogas has ethanol in it which is corrosive to rubber and aluminum, but there is not enough ethanol in mogas to be of concern.  My guess is that using gasoline as a flushing agent won't hurt anything.  I was just curious as to how many folks flush their systems versus just draining old oil and adding new oil.

[Hank]

I drain mine warm; if necessary, I will take a lap or two around the pattern to warm it up. [Darn it, honey--I have to go fly the plane a little bit.] Drain the oil out, leave to drain while I gather tools, finish decowling, fetch oil & filter, remove/replace/safety the new filter. THEN I pull off the hose and close the drain valve.

Refill everything, scribble notes for the logbook, and darn it, honey, I have to test-fly the plane to complete the maintenance. See you in a little while!

[aviatoreb]

Quote: Bill_Pyles

Well, lead is also a lubricant and I am only talking $6 worth of avgas.  Moreover, some mogas has ethanol in it which is corrosive to rubber and aluminum, but there is not enough ethanol in mogas to be of concern.  My guess is that using gasoline as a flushing agent won't hurt anything.  I was just curious as to how many folks flush their systems versus just draining old oil and adding new oil.

[KSMooniac]

Lead is NOT a lubricant.

[Shadrach]

Ethonal is corrosive to aluminum? That's a new one for me. Do you have a reference?

[jetdriven]

If you repeat something three times, it becomes fact.  Ethanol corrodes aluminum.  Theres #3.

[Lionudakis]

To do this as regular practice with oil change seems excessive, perhaps more work and expense than it gains.  To ask if lycoming approves is like asking about LOP, of course they're not going to approve. But sloshing, or even just letting it sit and draining it can't hurt anything, and it should be run after anyways to leak check, so that covers any bare steel/rust.

I did however drop a mag coupler pulling the mag off on a O-320 once, I drained the oil and  used a gallon of fuel to flush the coupler to the removed oil pump screen so I could fish it out, I pulled out 3 extras !

[Bennett]

I have been

doing this procedure for over 30 years on three Lyc. IO-360 engines and all of

them made it past TBO without replacing a cylinder. Here is the reasoning

behind it and the complete procedure.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

[Piloto]

I have been

doing this procedure for over 30 years on three Lyc. IO-360 engines and all of

them made it past TBO without replacing a cylinder. Here is the reasoning

behind it and the complete procedure.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

When you

drain the oil out of a hot engine you are actually leaving

[Piloto]

Sorry Bennet, another identity mix up

José