Clearing fouled plugs

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noahfong

Pre-takeoff checklist
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Noah
I was at a CFI meeting yesterday where the topic of clearing fouled plugs came up. Seemed everyone there said the way to do it was to go to full power (mixture full rich) for about 4 seconds.

Is that the way to do it? I've never tried it.

Back in the 80s-90s, I was taught to lean at runup rpm (~1700rpm) until just short of rpm decrease. Then advance to 2000rpm for 15-30 seconds. Seemed everyone did it that way back then. I still do it that way.

Has things changed or am I one of the few to do it differently? Any greater risks either way?

Thanks!
 
Lycoming says during your POST FLIGHT Run-Up.

They have a SI on this.
 
Much easier to just replace your spark plugs to UREM37BY or REM37BY and avoid fouling altogether.
 
wouldn't the procedure depend on the engine and the type of fouling?
 
noahfong said:
I was at a CFI meeting yesterday where the topic of clearing fouled plugs came up. Seemed everyone there said the way to do it was to go to full power (mixture full rich) for about 4 seconds.

Is that the way to do it? I've never tried it.

Back in the 80s-90s, I was taught to lean at runup rpm (~1700rpm) until just short of rpm decrease. Then advance to 2000rpm for 15-30 seconds. Seemed everyone did it that way back then. I still do it that way.

Has things changed or am I one of the few to do it differently? Any greater risks either way?

Thanks!
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Why plugs foul in the first place is a better thing to discuss than how to clear it. In my experience, taxing with a too rich mixture is a common cause. I recommend students to lean right after startup, to the point where the engine stumbles. Then richen it during runup.
 
kshaw said:
Much easier to just replace your spark plugs to UREM37BY or REM37BY and avoid fouling altogether.
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Curious, I haven’t heard that. How do those plugs avoid fouling altogether?
 
Doug Reid said:
teardrop entries
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sarangan said:
lean right after startup
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You are all nutso. Two of the most dangerous things you can do in an aero-plane. You probably run full throttle and over-square all the way to cruise, too. What's next? Leaning in the climb???

Danger to yourselves and everyone in a 20nm radius. Think of the children!
 
Deelee said:
You are all nutso. Two of the most dangerous things you can do in an aero-plane. You probably run full throttle and over-square all the way to cruise, too. What's next? Leaning in the climb???

Danger to yourselves and everyone in a 20nm radius. Think of the children!
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Why is leaning right after startup so dangerous? And what does that have to do with children :)
 
Deelee said:
It's not. Sarcasm.

Some students are told not to touch that horrible, fuel-starving red lever under any circumstance.
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That was a design flaw. A green knob for the mixture would have been friendlier.
 
Deelee said:
You are all nutso. Two of the most dangerous things you can do in an aero-plane. You probably run full throttle and over-square all the way to cruise, too. What's next? Leaning in the climb???

Danger to yourselves and everyone in a 20nm radius. Think of the children!
Click to expand...


It's too horrible.

Those from Phoenix still can't discuss the great Over-Square incident of 2018. The memories are too raw.
 
From Continental’s “Tips On Engine Care”:

“Never but never attempt to “burn out” a magneto drop with ground run-up. This “time honored” procedure succeeds only at the expense of the engine's mechanical health.”

Discuss…
 
sarangan said:
Why plugs foul in the first place is a better thing to discuss than how to clear it. In my experience, taxing with a too rich mixture is a common cause. I recommend students to lean right after startup, to the point where the engine stumbles. Then richen it during runup.
Click to expand...
Deelee said:
It's not. Sarcasm.

Some students are told not to touch that horrible, fuel-starving red lever under any circumstance.
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Teaching proper leaning procedure is required, but leaning on the ground can result in cylinder damage when the student fails to push the red knob forward for takeoff and full power for maneuvers in the practice area. The prudent flight school has a no lean on ground or in practice area policy to lower cylinder damage risk. At 50 hours the APs clean the plugs with the oil change.
 
Rather than discussing clearing plugs ad nauseam fixing the airplane should be discussed. There are a few engine types where even the most well maintained engine will occasionally foul a plug but they are the exception rather than the norm, if my experience of flying and maintaining aircraft is any indicator.

As usual, owners and pilots are far too accepting of substandard equipment.
 
Clip4 said:
Teaching proper leaning procedure is required, but leaning on the ground can result in cylinder damage when the student fails to push the red knob forward for takeoff and full power for maneuvers in the practice area. The prudent flight school has a no lean on ground or in practice area policy to lower cylinder damage risk. At 50 hours the APs clean the plugs with the oil change.
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That's a valid point which is why I teach leaning until the engine stumbles. For taxiing, that is almost near cutoff. I was going to say that is hard to miss if you push throttle to full, but stranger things have happened, so I will refrain from saying that.
 
Consider you are x miles out and descending.

As you reduce power you are also reducing Combustion Chamber temps.

As the Throttle is closed the Idle Setting of an even Richer Mixture kicks in.

The lower temps allow deposits build on plugs, pistons and heads.

The engine is hot after flight so a Post Flight Run-up will clear the fouling

readily.

Also it’s a good time to check mags and assure you are good to go for next flight.

Worked for USAF.
 
RyanB said:
Curious, I haven’t heard that. How do those plugs avoid fouling altogether?
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upload_2021-7-20_9-38-41.jpeg

The usual REM or UREM 38E or 40E plug on the left has a deep well that tends to hold deposits that pile up and short the electrodes. The REM/UREM37BY on the right has extended electrodes and a shallow well that discourages fouling. I used them in all the flight school engines that were approved for them. There is no RHM or URHM version for the larger engines.
 
FastEddieB said:
From Continental’s “Tips On Engine Care”:

“Never but never attempt to “burn out” a magneto drop with ground run-up. This “time honored” procedure succeeds only at the expense of the engine's mechanical health.”

Discuss…
Click to expand...
It can be engine-specific. A small engine is unlikely to suffer detonation doing that, while a larger engine, especially boosted, can easily get into trouble.

Doing this to burn out fouling only gets a bit of the crud off, just enough to get the plug firing again. That plug will foul again as soon as it can. The plugs need to come out and get cleaned, and other measures taken to reduce the fouling: leaning during taxi and cruise, and maybe installing the extended-electrode plugs or a hotter plug.

A burnout runup is just procrastinating on proper operation and maintenance.
 
Thanks everyone... BUT....

Let me do a quick reset... as much as I appreciate the info about plugs that resist fouling, advice about trying to not let the plugs foul, info about valve sticking, checking for plug fouling post-flight, etc.... yes - I appreciate all that - Thank you -

BUT....

Assuming there are some of you who do something to clear fouled plugs, what do you guys do when they DO foul? What technique do you use? I understand and respect the argument that says take them out and clean/replace them so I don't need to hear that again.

If no one answers the question this time, I will assume no one does it anymore. That's fine, too.
 
Ok...just exactly what do you want to hear ? It has been my experience that if you routinely have a fouled plug, you need to locate the culprit and remove it from the engine to see if you can determine if the plug is bad, has gone way up in resistance ( old Champion plugs ), or if there is an issue with the ignition lead.
Aggressive leaning during the run-up might clear the problem...if not I would investigate further...my 2 centavos..
 
Noah

I don’t believe you stated engine type?

Lycoming came up with the post-flight run-up to address this issue with the

O-235 L2C ( C-152) as it was a problem even with the BY plugs.

Build-up was so bad on Piston Tops that they would contact the Head.

Grit blasting in place with shells addressed that problem.

Many folks shut down the engine per AIRCRAFT mfg instructions.

Why not try it per the ENGINE mfg as stated in the Service Instruction.

What I saw was it did not help the issue; it eliminated it!
 
noahfong said:
I was at a CFI meeting yesterday where the topic of clearing fouled plugs came up. Seemed everyone there said the way to do it was to go to full power (mixture full rich) for about 4 seconds.

Is that the way to do it? I've never tried it.

Back in the 80s-90s, I was taught to lean at runup rpm (~1700rpm) until just short of rpm decrease. Then advance to 2000rpm for 15-30 seconds. Seemed everyone did it that way back then. I still do it that way.

Has things changed or am I one of the few to do it differently? Any greater risks either way?

Thanks!
Click to expand...

That’s how I was taught. Running full Rick is just adding more fuel to the situation, which I don’t see how that will assist in burning off the buildup on the plugs.
 
noahfong said:
Thanks everyone... BUT....

Let me do a quick reset... as much as I appreciate the info about plugs that resist fouling, advice about trying to not let the plugs foul, info about valve sticking, checking for plug fouling post-flight, etc.... yes - I appreciate all that - Thank you -

BUT....

Assuming there are some of you who do something to clear fouled plugs, what do you guys do when they DO foul? What technique do you use? I understand and respect the argument that says take them out and clean/replace them so I don't need to hear that again.

If no one answers the question this time, I will assume no one does it anymore. That's fine, too.
Click to expand...

https://pilotworkshop.com/tips/clearing_fouled_plug/

fwiw

That's what I did when flying a cherokee.
 
noahfong said:
Thanks everyone... BUT....

Let me do a quick reset... as much as I appreciate the info about plugs that resist fouling, advice about trying to not let the plugs foul, info about valve sticking, checking for plug fouling post-flight, etc.... yes - I appreciate all that - Thank you -

BUT....

Assuming there are some of you who do something to clear fouled plugs, what do you guys do when they DO foul? What technique do you use? I understand and respect the argument that says take them out and clean/replace them so I don't need to hear that again.

If no one answers the question this time, I will assume no one does it anymore. That's fine, too.
Click to expand...

FWIW, I suspect that most of the advice you’ve been getting is from an owner perspective. When you own the airplane and you are the only one flying it, you want to address the plug fouling issue properly.

Rental flying is a little different. You are often flying planes that multiple knuckle heads flew before you and taking it back to the line, calling the owner and telling them to change the plugs out with fine wires is just not a realistic option.

Back in my renting days, the procedure I was taught by flying club CFIs was run up at full power and then lean the mixture to rough, then enrich just enough to smooth. Usually no more than 30 seconds. Then pull power back to run up setting and recheck the mags.

As far as damaging the engine, we are talking about the majority of the rental fleet which is primarily 200 hp engines without constant speed props. Not likely to get those hot enough to damage.

For my personal airplanes, I’ve done plug fouling burn offs on occasion to maybe get home, but then applied long term solution once home. When you are trying to clear a plug on a 600 hp engine and you are watching the CHTs push past 400F, you kind of don’t want to make a habit of it…
 
Fearless Tower said:
FWIW, I suspect that most of the advice you’ve been getting is from an owner perspective. …
Click to expand...

THANK YOU! That is so astute of you. In actuality, I didn't have a problem...just heard in a meeting about this other method people were using and wanted to know more about it.

Fearless Tower said:
... knuckle heads …
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Love that technical term!

Fearless Tower said:
...When you are trying to clear a plug on a 600 hp engine and you are watching the CHTs push past 400F, you kind of don’t want to make a habit of it…
Click to expand...

Could only imagine ... thanks for the perspective.

Bob Noel said:
https://pilotworkshop.com/tips/clearing_fouled_plug/
https://pilotworkshop.com/tips/clearing_fouled_plug/
fwiw

That's what I did when flying a cherokee.
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That is also how I was taught. And I've used it successfully. It shocked me to hear about the full power, full rich thing. It was brought up in a meeting of around 15 CFIs... all seemed to nod in agreement. I asked an older CFI afterwards, thinking it was just a new, young CFI thing... but he only knew about that method.

TommyG said:
That’s how I was taught. Running full Rick is just adding more fuel to the situation, which I don’t see how that will assist in burning off the buildup on the plugs.
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I also don't see how it could work. That's why I asked the question. Thanks.
 
90% of the time, when you are "clearing" plugs at runup, you are removing carbon, which is both combustible and volatile, not lead, which is deposited as lead oxide, an is quite refractory once it builds up. Typically, you have to chip out lead oxide deposits on the plugs to get rid of it. And for sure the most efficient way to remove volatile deposits is to raise the combustion temperature and air/fuel ratio to prevent deposition of still more incomplete combustion products. So a leaner mixture during runup is the way to go. If it clears, it was likely carbon or oil.

When you have to start "clearing" plugs, you should start asking questions about why that is necessary. If you are getting "clearable" carbon deposits, that could be due to taxiing over-rich, or the result of oil blow by (in which case you might be burning off wet oil deposits from lower plugs, or partially combusted oil) You can largely eliminate #1 by aggressively leaning during taxi (that may help with lead deposition a little as well). If #2 is the problem, you need to find out why a cylinder is pumping oil and remediate it.

To prevent lead deposition, it is necessary to limit the amount of time the engine is operated rich, which will encourage deposition of non-volatile combustion products. One can also add lead scavengers, like TCP to the fuel. It works.

However, I have found that by aggressively leaning during taxi, and minimizing rich engine operation (as many might unnecessarily do during a long descent to the destination as per the checklist), I rarely get carbon or lead fouling, and don't find TCP necessary. Repeated oil fouling is a clue to consider refurbishing a cylinder. This is my observation in over 35 years of ownership of Lycoming engines.
 
Leaning during taxi will help.

However; I believe the issue begins with the Approach.

Low Power and Rich Mixture allow lead buildup due to low combustion chamber temps.

The Post Flight Run-up with a hot engine is easier to “ burn -off” deposits

than a cold engine.
 
I’ve lost count of the number of pilots I’ve flown with that upon reaching top of descent when attacking an airport that pull the power back and then go full rich at 3,500+ feet. Ugh.

They get an immediate lesson in engine management.


Sent from my iPhone using Tapatalk
 
True that prevention is best. But OP might be a student. Might be a renter. You can't control the engine use when you're not the sole user.

So throttle up to 1700 rpms, lean until stumbles then add back 1/2 turn. Let it run for 20 sec.
Should be good to go - but of course re-do a normal run up check to be sure.

And one piece of advice. Do a run up Post-Flight. Then you'll know if you have an issue before you hop in it next time (non-renter version)
 
Ravioli's true story time

I had a bad ignition check on my plane 2 months ago (O-320). First time in 6 years of ownership. A&P said, give it a good full power leaning and see if that handles it. Otherwise, I'll replace all the plugs... it's cheaper than cleaning them.

Note: EAB and auto plugs. YMMV
 
Ravioli said:
Note: EAB and auto plugs. YMMV
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There are some advantages to experimental aircraft and this is one. I generally replace my plugs every condition inspection whether needed or not. It costs less than $45 including shipping for a set of iridium plugs. BTW ... I've never fouled an iridium plug but I do lean aggressively for all ground ops.
 
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