100LL addivtives to reduce plug fouling

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Scott MacKie

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Have a mogas STC, not always available, is there an additive that can help reduce lead fouling of plugs if using 100LL?

Thanks
 
Scott MacKie said:
Have a mogas STC, not always available, is there an additive that can help reduce lead fouling of plugs if using 100LL?

Thanks
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Not so much of an additive, but pull red knob toward you until engine stumbles, then push in slightly. Plug fouling now minimized.
 
Lycoming published an SI that addressed fouling in the O-235L2C S in a 152.

During your Post Flight Run -up ( you do them?) at about 1800 RPM for 30 secs

you lean mixture.

Great time to check mags too!

One Flight School had issues and the technique eliminated the problem.
 
OK fella's I understand leaning. Do it all the time, lean before takeoff for density altitude, etc. I'll go find some Tom Cat ****.
 
Scott MacKie said:
OK fella's I understand leaning. Do it all the time, lean before takeoff for density altitude, etc. I'll go find some Tom Cat ****.
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REALLY lean it out. Like to the point that adding any RPM kills the engine.
 
It may seem obvious but make sure the engine is well maintained and running the best it can. I have had very little plug fouling trouble with any of the common flat engines that most people fly when they are properly cared for. That is with only a mediocre effort to lean the mixture as well.

And before someone feels the urge to point it out, yes I am aware that some engine models are more fussy than others. Some of the ones I am referring to are the fussy ones and they were in a training environment too.
 
Decalin is used by many ROTAX owners when forced to use 100LL, myself included.

Not sure it’s applicability to “legacy” engines.
 
The iridium plugs have been magic for me. Instant starts, smooth running and less wet dog shakes on shutdown.
 
The O-235 in the Early C-152s was the worst case for plug fouling. Even with TCP and constant leaning and the high RPM shutdown, the low-compression pistons made removal and cleaning of all eight plugs every 20-25 hour necessary.
 
eman1200 said:
right, because I have one of those "take away fuel" levers but I don't have an "add air" lever.
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Think about it. Fuel has mass and takes up space. If you remove some fuel from the intake port there is more room for air.

This is a big problem in high horsepower port injected applications and one advantage to direct injected engines.
 
mondtster said:
Think about it. Fuel has mass and takes up space. If you remove some fuel from the intake port there is more room for air.

This is a big problem in high horsepower port injected applications and one advantage to direct injected engines.
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so then we agree, the action taken is to reduce the fuel..........
 
IK04 said:
The O-235 in the Early C-152s was the worst case for plug fouling. Even with TCP and constant leaning and the high RPM shutdown, the low-compression pistons made removal and cleaning of all eight plugs every 20-25 hour necessary.
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We had a Citabria 7ECA with the O-235 and had to clean the plugs that often. Lots of time in the circuit made it like that. I finally replaced all eight plugs with UREM37BYs and the problem instantly disappeared. I also put those plugs in the other engines for which they were approved. The engine even runs better with them, since the spark is farther out in the air/fuel mix. I've sometimes wondered if there are sometimes exhaust gases lingering in the plug well of ordinary plugs that can inhibit ignition performance.
 
Dan Thomas said:
We had a Citabria 7ECA with the O-235 and had to clean the plugs that often. Lots of time in the circuit made it like that. I finally replaced all eight plugs with UREM37BYs and the problem instantly disappeared. I also put those plugs in the other engines for which they were approved. The engine even runs better with them, since the spark is farther out in the air/fuel mix. I've sometimes wondered if there are sometimes exhaust gases lingering in the plug well of ordinary plugs that can inhibit ignition performance.
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Ive always used 37BYs as well and have had similar results. Some of the old mechanics I’ve worked with refused to use them and thought I was dumb for doing so but I’ve always had good results even on engines known for fouling plugs.

The recess in which Lycoming likes to put their spark plugs is a mystery to me. It’s as if they went out of their way to create a collection point for oil and lead and intentionally reduce power and efficiency.
 
If you don't want to buy 8 iridium plugs, just get 4 and put them in the lower holes. That's what I did, and it worked perfectly. I also used TCP, and that helped but not nearly as much as the plugs.
 
FastEddieB said:
Decalin is used by many ROTAX owners when forced to use 100LL, myself included.

Not sure it’s applicability to “legacy” engines.
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As I understand it, it works fine on older engines but unlike TCP it's not approved for use on standard category aircraft, experimental only.
 
In my uncertified air cooled conversion engine I use Decalin (for experimental only - certified requires TCP) and the dreaded Marvel Mystery Oil in the fuel. I've even been known to use a bottle of engine cleaner containing P.E.A. (polyether-amine) every once in a while to help keep the engine clean.

Other than that it's about very aggressive leaning and the use of Iridium plugs. I use Mogas when I can get it but the octane requirement for my engine usually requires me to use some 100LL also.
 
Spark Plugs were just one of the lead issues on the O-235L2C.

Lead would build up on Piston Tops and strike the Cylinder Head!

You could feel and hear the contact .

Lycoming developed a procedure to blast the build up with wheat or rice

with the cylinders installed.
 
Nobody is pointing out that if it's an STC then the engine was designed to run on leaded fuel to start with. If it's fouling technique or something else is wrong. MoGas isn't the as solution, it's just masking the problem.
 
denverpilot said:
Nobody is pointing out that if it's an STC then the engine was designed to run on leaded fuel to start with. If it's fouling technique or something else is wrong. MoGas isn't the as solution, it's just masking the problem.
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Not necessarily. 100LL has a lot more lead than the 80/87 many older engines were designed to run on. An engine designed to run on 80 or lower (the A-65 in my T-Craft specified 73 octane minimum) will have lead fouling issues on 100 even if it's in perfect shape.
 
The best medicine is leaning as much as possible without killing the engine while on the ground. My first reaction to an additive that claimed to prevent spark fouling would be to think of it as snake oil.
 
Dana said:
Not necessarily. 100LL has a lot more lead than the 80/87 many older engines were designed to run on. An engine designed to run on 80 or lower (the A-65 in my T-Craft specified 73 octane minimum) will have lead fouling issues on 100 even if it's in perfect shape.
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Yup. From memory, when I taught Aircraft Systems in college:

80/87 (now known as 80) had 0.5 ml/gallon of TEL (note the silly mix of metric and US measures). 73 octane would have had even less lead.
100/130 (known as 100) had 4.0 ml/gallon. That stuff really fouled plugs in little low-compression engines. Eight times the lead of 80/87.
100LL has 2.0 ml/gallon.

I looked up current all-metric numbers on Wiki:

80 .14 g/l
100LL 1.12 g/l
100 .56 g/l
115/145 (115), the old warbird fuel, had 1.29 g/l. Seems to me there are racing fuels still available with that chemistry.
 
Dana said:
Not necessarily. 100LL has a lot more lead than the 80/87 many older engines were designed to run on. An engine designed to run on 80 or lower (the A-65 in my T-Craft specified 73 octane minimum) will have lead fouling issues on 100 even if it's in perfect shape.
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Most were listed as not only the 80/87 but also the purplish stuff in the POH. Unless they were some 70s newcomer to the block that wasn't originally a 1930s tractor engine.

This stuff is ancient.

People were putting total garbage fuels thru them before I was born.

It's mainly technique as others have pointed out. Lean aggressively on the ground means enough the engine will die if you advance the throttle.

All the oldsters knew this. Their other equipment and their cars needed it when they were kids.

It ain't the MoGas. That's all I was saying. These engines barely care at all what's put thru them if they aren't a turbo model. Especially carbed ones.

As my altitude aggressive leaning is pretty much always a requirement.
 
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