Too lean, too rich... nothing works

[A64Pilot]

25 minutes ago, MikeOH said:

@GeeBee

Great article!

Now, I'm wondering if I have a blow-by problem!  I use about a quart every 6-8 hours, and it turns black pretty fast.  But, compressions are all above 75.  Is there a specific test for blow-by to determine if it is excessive?

If you pass the compression test, your blow by is within limits, the compression test is of course actually a “leak down” test and determines both how much leakage there is, and where it’s coming from.

There have been tests using I believe an altimeter or maybe an airspeed indicator connected to the crankcase vent to determine running blow by, I have never done it, maybe it was a Continental thing?

I’ll see if I can find something, or maybe I’m confusing it with something else.

[GeeBee]

37 minutes ago, MikeOH said:

@GeeBee

Great article!

Now, I'm wondering if I have a blow-by problem!  I use about a quart every 6-8 hours, and it turns black pretty fast.  But, compressions are all above 75.  Is there a specific test for blow-by to determine if it is excessive?

I seriously doubt it. One your compressions are good and two, a quart every 6-8 is not really that excessive.

 

[GeeBee]

1 hour ago, MikeOH said:

@carusoam

Makes sense.

However, item 4 on my already done list was having the oil cooler overhauled by Pacific Oil Coolers.  Made zero difference.

I've seen new coolers make a world of difference from even recently overhauled ones. Like I say, they are cheap enough to find out.

[A64Pilot]

I found this, but it’s for a Continental 

https://www.csobeech.com/files/TCM-SB-M89-9.pdf

Excessive crankcase internal pressure is likely from excessive blow by. I know of nothing like this for a Lycoming

[MikeOH]

1 minute ago, GeeBee said:

I've seen new coolers make a world of difference from even recently overhauled ones. Like I say, they are cheap enough to find out.

Hmm, never considered that.  I think I'm going to try replacing the vernatherm first.  Then consider a new cooler.

[carusoam]

When it comes to blow-by…

When the oil turns dark really quickly…. That’s a sign….

When the oil turns foamy after a flight… That’s another sign…

When the oil smells like exhaust… That’s probably a third sign…

M20C memories I’m trying to get past…. 

Best regards,

-a-

[Ragsf15e]

2 hours ago, MikeOH said:

@GeeBee

Great article!

Now, I'm wondering if I have a blow-by problem!  I use about a quart every 6-8 hours, and it turns black pretty fast.  But, compressions are all above 75.  Is there a specific test for blow-by to determine if it is excessive?

What kind of cylinders are they?  Chrome have more blowby and oil use based on how they break in the rings vs “channels”.  6-8 hrs / qt would be pretty good for chrome.

[MikeOH]

1 hour ago, Ragsf15e said:

What kind of cylinders are they?  Chrome have more blowby and oil use based on how they break in the rings vs “channels”.  6-8 hrs / qt would be pretty good for chrome.

Good question!  I need to check. IIRC, there is a color 'stripe' that indicates...what color is chrome?  Naturally, sitting here on the couch, I can't remember what color is on mine!

[Will.iam]

7 hours ago, carusoam said:

When it comes to blow-by…

When the oil turns dark really quickly…. That’s a sign….

 

Define quickly. After 10 hours from oil change? 5 hours? 1 hour?

 

[Ragsf15e]

11 hours ago, MikeOH said:

Good question!  I need to check. IIRC, there is a color 'stripe' that indicates...what color is chrome?  Naturally, sitting here on the couch, I can't remember what color is on mine!

Orange is chrome.  It should be a pretty obvious color stripe.  They aren’t very common anymore but mine has them from a 1998 overhaul.  Eventually the chrome plating flakes off and you have to get them overhauled, except many places don’t do them anymore, so I have 3 chrome and one steel.  Anyway, chrome is notorious for blowby and higher oil use just on how they work.

[A64Pilot]

Lycoming max allowable oil consumption formula

0.006 x BHP x 4 ÷ 7.4 = Qt./Hr.

If I do the math right a 200 HP motor is allowed to use .65 quarts an hour or 6.5 quarts every 10 hours.

‘So 1 quart every 6 to 8 is well within limits

Lycoming color codes, the old chrome barrels had the whole circumference of the jug right at the base colored orange.

https://www.lycoming.com/content/understanding-engine-color-codes

 

Edited July 8, 2021 by A64Pilot

[EricJ]

16 hours ago, MikeOH said:

Good question!  I need to check. IIRC, there is a color 'stripe' that indicates...what color is chrome?  Naturally, sitting here on the couch, I can't remember what color is on mine!

It's usually the fins between the pushrod tubes that have the color code.   On mine they're blue to indicate nitrided.

https://www.lycoming.com/content/understanding-engine-color-codes

Edited July 8, 2021 by EricJ

[carusoam]

18 hours ago, Will.iam said:

Define quickly. After 10 hours from oil change? 5 hours? 1 hour?

 

hours…

As in… normally, you may go 10hours before adding a quart to your engine… and the oil slowly changes darker over the months….

With blow by… there is an obvious change…

Of course I have only had this happen once… in my old M20C…

Check the oil level after the flight… if you see foam, the oil smells like exhaust, and the oil got darker…  that is what I was seeing…  

PP thoughts only, not a mechanic…

Best regards,

-a-

[Will.iam]

Mine darkens at approx 10 hours. Doesn’t foam. Haven’t tried smelling it for burn smell yet that’s a new one for me. But by 30 hours the oil looked so black I didn’t want to push it and changed it.