AVGAS used to flush crankcase at oil change?

[Bill_Pyles]

KSMooniac---lead is indeed a lubricant.  Google "lead as lubricant in fuel" and you will find many references to the use of lead as a lubricating additive to fuel.

[PTK]

Quote: Bill_Pyles

KSMooniac---lead is indeed a lubricant.  Google "lead as lubricant in fuel" and you will find many references to the use of lead as a lubricating additive to fuel.

[RJBrown]

Quote: allsmiles

In fact, TEL (Tetraethyl Lead) is added to avgas in order to increase the fuel's margins or resistance to detonation. Thereby enabling the advantageous use of high octane fuel which is required for high piston engine performance at altitude. 

[KSMooniac]

Lead is most certainly not a lubricant...it is only a component to increase octane in our fuel.  The APS crew has a good bit of data dispelling this myth in their course.

[RJBrown]

Quote: KSMooniac

Lead is most certainly not a lubricant...it is only a component to increase octane in our fuel.  The APS crew has a good bit of data dispelling this myth in their course.

[Bill_Pyles]

In any event, I am going to put a gallon of AVGAS (per Jose) in the empty sump for 15 minutes and then let it drain out and take whatever old oil and other crud might be lurking.  I will then close the valve, install a new filter and fill the sump with 8 qts of new oil (Aeroshell W100) and be done with it.  No alumimum will be corroded, no bearings will have a chance to rust in the Arizona heat and I will have a cleaner sump than I would have had.  Any residual fuel will  either evaporate or blend with the new oil and will be gone in no time.

[danb35]

Sounds like you're convinced, and I don't see it doing any harm--but I'd use 7 quarts instead of 8, as you'll likely lose the 8th quart within a few hours anyway.

[jetdriven]

You can shake the plane to agitate the avgas, and stir up anything to be flushed out.  I wouldn't worry Bill.  Worst case, you waste 6$.  It costs more to start up that Mooney after changing the oil to check for leaks.

 

 

[DaV8or]

Quote: RJBrown

It is a very real question to collectors of 50+ year old cars.

[FlyingDude]

After 12 years... any further insights into this topic?

[shawnd]

  

9 hours ago, FlyingDude said:

After 12 years... any further insights into this topic?

A suggestion: after you have run the engine, let it sit for a day or two, or may be 5. Let the oil that is covering all the engine parts drip down and into the sump. Reason: if you have ever taken a look at your oil dipstick the day after  or a few days after, you will notice the level in the sump always rises. Drain after a sufficient time passes. Similarly take out your oil filter or use the pierce trick to let the oil drain out from the accessory side as well for a few days. By the time you come back to drain from sump, the oil on filter side of the engine should have left the engine by now.

I believe this maximizes one's opportunity to get all the "old" oil out.

[Utah20Gflyer]

I think it’s a waste of time.  Get oil analysis to get objective information about the quality of oil at the time you change it.  If it tests fine then continue on.  If it doesn’t then shorten your oil change interval.   
 

The practice of trying to get every drop of oil out of the engine is based on emotion in my opinion rather than a logic.   Engines that get ran a lot will last a long time.  The engines that sit don’t last.   That last bit of old oil just doesn’t matter.  

[ArtVandelay]

I run the engine (45 min flight ) with 1/2 quart of MMO before I do the oil change, helps clean all the internal parts, not just the crankcase. Thins the oil a little to help draining.
Also, Mooneys squat with nose up, lowering the nose will help drain more of the oil out, I partially pull the plane out of the hangar to do this.

[shawnd]

6 hours ago, ArtVandelay said:

I run the engine (45 min flight ) with 1/2 quart of MMO before I do the oil change, helps clean all the internal parts, not just the crankcase. Thins the oil a little to help draining.
Also, Mooneys squat with nose up, lowering the nose will help drain more of the oil out, I partially pull the plane out of the hangar to do this.

Curious if MMO affects oil analysis?

[wombat]

Regarding avgas in the oil.....  Some 182s have a 'oil dilution' option, which pumps some avgas into the oil, thinning the oil to make it easier to start.   If Cessna (I know, I know, they don't know the first thing about airplanes and engines) thinks avgas is OK to add to the crankcase occasionally,  I suspect some avgas (even a lot!) isn't going to hurt during an oil change.

 

But also, the contaminants are mostly spread evenly in the oil and developed evenly over time.  Getting the last 1/2 quart is 6.25% if you refill to 8 quarts, 4.2% if you use 12.  That is the same as changing the oil 1.875 (1.278 for a 12 QT sump) hours earlier if you change on a 30 hour schedule.    I don't pay the slightest bit of attention to going 2 hours over my 30 hour interval.

 

Let's see... Cost analysis time...    

1 gallon of avgas = ~$7

1 oil change = 8 quarts at $7 + 1 filter @ $50, so let's say $100 total. 

If you change oil every 30 hours, oil changes cost you $3.33/Hr, and the reduced oil change interval going to 28 hour intervals would cost you $6.66, because that's 2 hours of flying you lose.

If you add the avgas but keep your oil change interval, that costs you $7..... Basically the same.

 

There is no way I'd track my flying budget that closely.  

[FlyingDude]

I think the purpose of this operation was not to shake or milk the final drops of oil out of the sump or the entire engine.  I think the purpose is to loosen and flush out the sediments that accumulated on the bottom of the oil sump - if there are any.  

Does gunk really settle on the bottom of the sump?  Does it really get flushed out with avgas?

[ArtVandelay]

Curious if MMO affects oil analysis?

Oil analysis looks for metals, MMO doesn’t have any I think, but avgas does and your lead content should be higher.

[PT20J]

On 3/21/2024 at 6:33 AM, shawnd said:

Curious if MMO affects oil analysis?

MMO is Naptha, Stoddard Solvent, TCP (lead scavenger) , o-, p-Dichlorobenzene (carbon dissolver), red dye and wintergreen fragrance. I doubt it would show up on oil analysis.

https://wiki.lbto.org/pub/Safety/ChemicalSafetySDS/Marvel_Mystery_Oil.pdf

Edited March 22 by PT20J
Fragrance is wintergreen not peppermint as originally stated.

[philiplane]

In theory, flushing with avgas will remove more oil. But it will remove less particles, because avgas is much lighter than oil and does not have good hydraulic properties. Meaning, you will remove the most particulate matter by draining the oil when it's hot. If you flush with avgas after that, you will remove any remaining oil in the pan. Which is very little. But if there are particles in the pan, the avgas will not remove them. It's too light.

[FlyingDude]

@philiplaneit makes sense. Thanks.

[carusoam]

Dude!

This was a favorite topic for José…

He used avgas to wash the sludge out of the oil pan…

Sludge is a mixture of 100LL additives and oil….

it has a tendency to pile up on the bottom….

 

the challenge being….

it is hard to tell how much of the gallon of gas actually drained back out….

any gas left behind in the oil, will evaporate as it gets hot…

but it also affects the viscosity…. This is where most people decide that it is very challenging to get this right…

it would be really cool to have clean looking oil for 50 hours…. Instead of it changing colors after the engine is first started…

PP thoughts only, not a mechanic…

Best regards,

-a-

[FlyingDude]

Hey A,

"Sludge" is the key word!

Well, we're told to fly the plane every 2 weeks rather than just let it idle to keep the engine well lubed and so that the oil reaches high temperatures and the water content evaporates. Avgas evaporates way before water...

But then there's the lead contamination into engine oil that leads to corrosion. I've read about it in many places but this is the top hit on my Google search' https://www.aopa.org/news-and-media/all-news/2017/february/24/why-change-the-oil

"To make matters worse, avgas is heavily laced with the octane improver tetraethyl lead (TEL), which also does nasty things when it blows by the rings and gets into the crankcase." 

TEL evaporates a little before water so you'd think it'll get expelled through the breather - but will it? Or will it just sit there and contaminate all the oil?

Maybe a good flush with UL94 would be the safe way to go...

Take care 

[PT20J]

Does either Continental or Lycoming recommend this?

If you use AD oil and change it frequently, it keeps the gunk suspended (that’s why it turns black).

Straight mineral oil will form sludge and Lycoming recommends not switching to AD oil if you’ve been running mineral oil for a long time because the detergents loosen the sludge and can cause it to clog oil passages. 

[Andy95W]

1 hour ago, PT20J said:

Does either Continental or Lycoming recommend this?

If you use AD oil and change it frequently, it keeps the gunk suspended (that’s why it turns black).

I agree with Skip.  This seems like a solution looking for a problem.

[Will.iam]

Blackstone lab knows when you use or suspects when MMO is used as the viscosity of the oil is lower than what’s normal. That’s why tgere is a section on the form for listing additives and how much you put in so they can account for the lower viscosity value. Blackstone labs could also tell when i started running lean of peak ops as there was lower fuel  contaminants and when i started running a dehumidifier they noted i had little to no water in my oil samples and asked me what i was doing differently to account for the change.