What do you think of the gray color of this exhaust oil?

**RknRusty** Thu Apr 19, 2012 9:57 pm

I didn't want to hijack my own Bat thread, so I'm posting this here as another discussion.
As long as I can remember the exhaust residue was always grayish. I never thought much of it until I began hearing others talk about signs of a dying engine. So now I worry about it. Y'all already know how I tend to over think everything before finally simplifying it. So, I just want to know what you think of this residue left by my Medallion a few minutes ago.

What do you think of the gray color of this exhaust oil? Th_0419122156

What do you think of the gray color of this exhaust oil? Th_0419122156

I had decided to put a 6x3 Cox on it for the next test flight of the new Bat. But it only tached at 13,500 RPM. So to make sure it was stiull running okay, I put another APC 5.5x2 on it. It tached at 20,300RPM, same as the other day when it had the G/N head on it, but it has a Babe Bee head now. So for my next test flight tomorrow(the weather was uninspiring today), I put a Cox 5.5x3 on it. I didn't test run it because I'm tired of burning up fuel. But anyway, when I was cleaning it, I thought I would ask your opinions on the gray color of the exhaust. I looked at it under the magnifying lamp and cannot see any metallic sparkles.

Does this look like trouble, or normal exhaust?

microflitedude Thu Apr 19, 2012 10:03 pm

Running an engine at 10:30? Good lord... Very Happy

**Cribbs74** Thu Apr 19, 2012 10:15 pm

Dab your finger in that residue and take a look at it under a magnifying glass. If you see any particulates then you may have a problem. It's probably just the fuel your using or crap in the air it's sucking in.

**RknRusty** Thu Apr 19, 2012 10:21 pm

microflitedude wrote:Running an engine at 10:30? Good lord...

When the inspiration strikes... I just have to.

cribbs74 wrote:Dab your finger in that residue and take a look at it under a magnifying glass. If you see any particulates then you may have a problem. It's probably just the fuel your using or crap in the air it's sucking in.

I did that. I can see nothing, no sparkles, no speckles, just smooth gray at that low magnification. You're probably right. I'm using Glowplugboy, formerly 24% until I added 3% more castor to bring it up to 20% oil. It's cheap Rexall pure castor oil.

**Admin** Thu Apr 19, 2012 10:30 pm

I have seen the gray residue myself before as well. I didn't see any shiny particles either. It could be a layer of corrosion that is getting removed as it usually only does it to engines that were first started in many years.

**RknRusty** Thu Apr 19, 2012 10:49 pm

I think I'm probably okay, just thought it was worth some extra opinions. I might break out the pocket microscope and give it a closer look before I clean it up tomorrow. I think it goes up to 100x magnification.
Thanks for the replies.

On another subject, that's a helluva drop in RPM between the Cox 6x3 prop, and the APC 5.5x2. Down to 13,500 from 20,300. I'll tach the Cox 5.5x3 when I go out to fly tomorrow. I just wish those APCs weren't so rigid. But they sure are easy to balance.

John Goddard Fri Apr 20, 2012 1:37 pm

Doesn't sound bad to me Rusty when mine was black and gooey
Recently we concluded it was the fuel dying not the engine.
A switch to some new stuff cured it.
I did blow the bejesus out of the mota 5'or 6 tanks later
But that was operator error tho.
It's the dark brown (lean) toasted oil you need to avoid.
J

**RknRusty** Fri Apr 20, 2012 3:06 pm

John Goddard wrote:Doesn't sound bad to me Rusty when mine was black and gooey
Recently we concluded it was the fuel dying not the engine.
A switch to some new stuff cured it.
I did blow the bejesus out of the mota 5'or 6 tanks later
But that was operator error tho.
It's the dark brown (lean) toasted oil you need to avoid.
J

Sounds like what I wanted to hear. I've never had an engine spew brown cooked oil. Nor have I ever actually blown an engine in all my hobby years. Had a couple get loose compression on me though. One of those may have been an Estes.
Thanks John.

nitroairplane Fri Apr 20, 2012 4:03 pm

I mean what's gray oil anyway?

**RknRusty** Fri Apr 20, 2012 9:52 pm

nitroairplane wrote:I mean what's gray oil anyway?

It must be what remains of the spent volatiles. Carbon, maybe. I'm texting my chemist son right now. I'll be back with his answer.

He texted back and said it's probably carbon black that tints the exhausted oil. So the oil is not gray, it's got to be something in it. Unburned castor is clear unless there is an overheat problem, then like John said, it will be brown.

Surfer_kris Sat Apr 21, 2012 12:17 am

Sounds like you have something that rubs on aluminium. This gives a black or gray colour to the oil without any metal particles. Try to check if it is actual exhaust residue or oil from another part, like a the front end. It could be something as simple as a starter spring vibrating and touching the case, or a muffler that vibrates against the cylinder and/or crankcase.

Ivanhoe Sat Apr 21, 2012 5:23 am

i think that horse needs to be shot! lol!

Kim Sat Apr 21, 2012 7:44 am

RknRusty wrote:
nitroairplane wrote:I mean what's gray oil anyway?
It must be what remains of the spent volatiles. Carbon, maybe. I'm texting my chemist son right now. I'll be back with his answer.

He texted back and said it's probably carbon black that tints the exhausted oil. So the oil is not gray, it's got to be something in it. Unburned castor is clear unless there is an overheat problem, then like John said, it will be brown.

OK...this forum needs to draft somebody with one of them spectro-laser-flux-capcitor-amalgogramaphonic-electron-collide-o-scopes !

**RknRusty** Sat Apr 21, 2012 8:01 am

Ivanhoe wrote:i think that horse needs to be shot!

Aw man.

So now this is the good news bad news thread. It runs good, but it is turning a little faster at peak than the graph shows it's supposed to.

Kim wrote:OK...this forum needs to draft somebody with one of them spectro-laser-flux-capcitor-amalgogramaphonic-electron-collide-o-scopes !

I think PV, the mad scientist, has one of those in his laboratory. I have a Radio Shack microscope, I'll see if i can find it.

Kim Sat Apr 21, 2012 8:08 am

RknRusty wrote:
Ivanhoe wrote:i think that horse needs to be shot!
Aw man.
So now this is the good news bad news thread. It runs good, but it is turning a little faster at peak than the graph shows it's supposed to.

Kim wrote:OK...this forum needs to draft somebody with one of them spectro-laser-flux-capcitor-amalgogramaphonic-electron-collide-o-scopes !
I think PV, the mad scientist, has one of those in his laboratory. I have a Radio Shack microscope, I'll see if i can find it.

I hear that, when engaged, they draw down the lights in the neighborhood like Chevy Chase's Christmas Lights in "Christmas Vacation" !

**RknRusty** Sat Apr 21, 2012 8:24 pm

I flew the Com Bat today. The starter spring is rubbing on the bottom of the drive plate. Most of the exhaust goo is pink and clear. the goo on the bottom behind the rub is where the gray is coming from.
Much ado about nothing, but thanks for the replies.

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What do you think of the gray color of this exhaust oil?

What do you think of the gray color of this exhaust oil?

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I found the source of the gray oil.

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