downunder

This is another myth that probably started when someone got some hot oil on their finger by getting too close to the muffler outlet. The only function of oil is to reduce friction heat by lubricating, nothing more.

But the myth continues. Now the volume of oil coming out of the engine through the exhaust exactly balances the volume of oil going in through the carb with the fuel. Naturally. But what's the volume per cycle that everyone says takes heat from the engine? It's actually fairly easy to work out. All you need to know is how much oil is in a tank of fuel, how long the engine will run on that tank and what revs it's doing during that tank.

Take a sample engine for instance. Fill a 300cc tank (sorry about metrics for the uninitiated but it's easier ) with a fuel having 20% oil. That means the tank has 60cc of oil in it. Start the engine and it runs flat out at 10,000 rpm and it runs for 10 minutes on that tank. In that 10 minutes it's used 60cc of oil. But also in that 10 minutes the engines has turned 100,000 times. This means that every cycle .0006cc of oil goes into the engine. But oil in=oil out so every time the exhaust opens .0006cc of oil comes out.

OK, I'll do it in American
10 ounce tank
2 ounces of oil
100,000 revs
0.00002 ounces/rev

These are just off the top of the head figures but are probably fairly close to real world engines.

The point being that there's such tiny amount of oil passing through it simply can't take out any appreciable heat.

jaka

Hi!
But you agree that our glow engines are cooled by the methanol in the fuel..!!???

wjvail

My Feedback: (3)

I complete agree with this. It is one of the primary sources of cooling.

Running more and more oil forces the fuel air mixture ratio to be closer and closer to perfect to achieve any reliable performance. I think we would all agree that there is some amount of oil in our fuel where the engine won't run at all. Say it's 37% oil. At some point just below that number, say 36%, the engine will run BUT the mixture must be full goose lean or the engine will quickly drop into a lean 4 Cycle and most likely die. You find yourself in the odd situation of running a ton of oil, the engine is running in a sloppy 4 cycle blowing tons of smoke at 7,000 rpm and is full lean and it's 300+ deg. The acceptable band of needle tuning becomes literally one click between running "rich", "perfect", and dead lean and in all cases, it runs HOT. I use this extreme example to point out that as you reduce the amount of oil (to a point) you improve the overall handling of our engines. At 14% oil you will find the needles are very broad and tolerant of being set on the rich side. You can back the needle off by a 1/2 turn and the engine will run a lot more fuel thought it and at the same time performance with not degrade as quickly. You may be 200 rpm off peak but still have outstanding idle, power and transition and because it is running much more fuel through the engine, it will be running very much cooler. As you add more and more oil you will sacrifice all of these.

I would suggest the hamfisters need LESS oil! It makes the engine much easier to tune.

Bill Vail

wjvail

My Feedback: (3)

Hmmm... I don't think that tells the whole story. In it's most simple terms I would agree with you... BUT, over the years I've met many folks that add oil to their fuel at the cost of engine reliability. If the engine lasts 30 years but dead sticks every 3 fight are you better off? What do you think is a reasonable life span for a model engine? Are you will to accept more dead sticks (and wrecked airplanes) to extend this. You can run over 30% oil (I've done it) but you need to be and exceptionally good tuner and even better at dead stick landings.

I also have many older engines (over 300 total to include an OS 60H gold head). There are ABC engines, ABN, ABL, AAC, ringed and what I call SIV engines. SIV is Steel, Iron and Varnish. For these engines with their heavy, soft iron positions I run all castor. All others are a blend of mostly synthetic and some castor.

Bill Vail

NM2K

My Feedback: (14)

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I can't imagine anyone running more than 30% oil. Duke's Superfuel, IIRC, used to contain 28% castor oil. Of course, when I was using that goop I was flying non throttled control line engines.

I don't accept deadsticks at all. No need to do so. I sometimes add four ounces of castor to fuel that I know will be consumed by plain bearing engines. Otherwise I do not bother with it. It isn't needed.

Contrary to popular opinion (so it seems) I am not committed to burning fuel with huge amounts of castor oil, or synthetic oil, in my engines. But if I had to err, I would go with more oil than less oil every time.

I do look out for engines that have unbushed connecting rod wrist pin areas or plain bearing main journals. The latter two will not last long even when burning castor oil lubed fuel if the mixture happens to lean out a bit too much.


Ed Cregger

Motorboy

See near at the pic, where are worned screw holes at the mounting lug? The engine are unused and zero worned parts...

Jens Eirik

NM2K

My Feedback: (14)

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I just bought a front and rear intake version of the engine you have pictured in your post.

I had the front intake version around 1970 or so NIB, but job demands crowded out the hobby, so I sold it without running it. Now I'm catching up. <G>


Ed Cregger

Sport_Pilot

Methanol is the fuel that is the source of heat. The reason engines run cooler when rich is because less of the methanol burns and the temperature doesn't get as high. There is some benefit from vaporization of fuel, but it is incomplete and a richer mixture does not make more fuel vaporize.

Consider this, our engines run rich of the stoichiometric. ideal because as they approach that the fuel will detonate. When we say the engine runs lean it may still be rich of a perfect stoichiometric mixture because of the ignition timing of the glow plug. Ignition engines can get to that point but only just lean of the stoichiometric ideal. The only engines that can run much leaner than the ideal mixture are turbines. Early turbine engines did not have turbine blades that could take the extreme heat of an ideal mixture, so to keep them cool they ran excess air, which is better than too rich because of the more complete combustion and the fact that moving that air is part of the thrust. However, as they found alloy's which can take that heat they created high bypass designs so that the power turbines ran with leaner mixtures, at higher heat, and more thrust.

So the short answer is that methanol does not carry heat away, it is the source of the heat. More oil or a richer mixture is a poor way of keeping an engine from overheating as this is robbing it of the heat which powers the engine.

wjvail

My Feedback: (3)

I was wondering if someone would catch me on that. You are right. The one pictured is un-run. It's sister engine was the Black Head .60H. I have several of those also. This one has been installed in my boat since High School over 27 years ago. This one is still going strong.

Bill Vail

Sport_Pilot

I had the black headed version.

TimC

It would seem there would be a quenching effect as the fuel/air moves through the engine and into the combustion chamber. I would think that methanol would quench better than oil.

wjvail

My Feedback: (3)

Touch the area between the bearings on your running two stroke or the intake tube on your 4-stroke and tell me that their isn't considerable cooling from the methanol. It is the primary source of cooling.

Why is the bottom end of a two stroke cool and the bottom end of a four stoke very much warmer?

Put some fuel on the back of you hand and blow on it. What does it feel like?

Bill Vail

Sport_Pilot

The quenching effect is the fuel vaporizing from liquid to gas. It is a rich mixture so it is saturated. That means that if you add more fuel the additional fuel will not vaporize, so no added quenching effect. However, the additional fuel will not burn and will in fact cause the rest of the fuel to burn incompletly which means it will not burn at as high of a temperature and the engine will also not have as much power.

Sport_Pilot

No the cooling fins are the primary source of cooling the fuel is a source of heat. That fuel does cool the incoming air, but additional fuel will not make it any cooler.

jaka

Hi!
When is white colour white and black colour black...???

This discussion is really fun to follow.
Ofcourse the engine gets cooled by emitting heat from it's aluminium case ...weather it's from the head fins or from the crankcase it self...or from both... really doesn't matter.

It's a well known fact that running a engine rich makes it run cooler...weather this cooler running condition comes from not taking out much power from the engine or that heat is exhaused through the excessive amount of methanol used...or oil... that floats/rushes through the crank up through the combustion chamber and out through the exhaust...does it really matter!?

Sport_Pilot

No, but for someone who may want to do modifications or design, then knowing the differance could make a good or bad design.

radcon56

I think,if those engines were maintained on a regular basis,they wouldn't be so gummed up.

buzzingb

My Feedback: (2)

I asked the question a few days ago about after-run (ATF )oil helping soften such deposits. I believe ATF would at least help soften these kind of deposits and allow the piston to run cleaner not clean just cleaner. I have never seen any such deposits on any of my engines but it may be the fuel I use and how I run them. I do use fuel with some castor and ofter add Castor and I run my engines pretty hard and fast.

proptop

My Feedback: (8)

A couple of years ago, when I first got one of those little blue Duratrax temp. checkers I measured the temp. of everything in sight.
I recall the lower case temp of a running TT .46 was something like 60-65 degrees while the head area was close to 200...
Ambient temp. was in the 70's.

downunder

Sorry S_P but that's wrong. All gas turbines run at stoichiometric in the actual burning part of the combustion chamber. The fuel nozzles are protected from direct airflow by a shield with small holes in it to allow enough (reasonably stagnant) air to support full combustion. Slightly downstream from this the combustion chamber (all types) have many extra holes to allow air to flow through them and be heated by the combustion flame. This air also cools the skin of the combustion chamber and cools the heat of the flame to a temperature the turbine blades can tolerate. The power turbine (last stages) for a fan engine are last in line to get the heat from the core engine. By pass air normally isn't burnt at all other than in an afterburning turbo fan engine. With a pure jet, or the core engine in a fan jet, only about 5% of the air is actually used in combustion.

blw

My Feedback: (3)

Air is also heated by the compressor section. Air also helps shape the combustion flame to the right shape. Some turbines have a drain system to protect the aft bearings once the engine is shut down. The synthetic oil burns and sludges, which isn't good for the bearings. There is a dump valve to drain the oil away from the bearings on shutdown before overheating. I'm speaking about the Allison 300 series on the bearings.

The cooling properties of oil in glow engines has been documented in enough places to dispel the myth that someone had their hand burned at the muffler.

Running an engine too hot or too lean with synthetic oils sometimes actually produces even more heat from the synthetic oil breaking down and burning. Castor breaks down to the varnish everyone is talking about.

Turk1

Sorry but I dont agree fuel helps cooling.Evaporating fuel functioning as heat pump,taking heat from crankase into the combustion chamber.Simply evaporating fuel wont leave engine carrying payload heat with it.

yallaair

Back to the carbon deposits in the small 2-strokes!
As long as you are operating the engine in a way that gives high combustion chamber temperature (lean running and high revolutions), castor oil WILL form deposits on the piston and other hot surfaces! Theese deposits are often referred to as a "lubricant". It's not. This varnish is polymerized castor oil that has decomposed, and acts like a emergency lubricant at high temperatures! And continous operating at high temp will cause substantial carbon build-up on piston and exhaust ports. This will again give more friction / restrict exhaust gas flow and give higher temperatures! Carbon on pistion will after some time give liner polishing that results in excessive liner wear.
Based on this, as long as you are operating the engine slightly rich, there is no advantage with castor oil. Castor oil has high viscosity that give high friction. Friction is power loss and give high temperatures. I never use castor oil, and none of the engines ( Enya 4c, Saito, OS airplane, TT heli, K&B marine, car engine etc.) has taken any damage so far... I use max 15 % synth oil.

There is no oil that will save your engine from abuse, not even castor oil.

yallaair

Turk1!
You are partially correct! The heat transferred from the cranckcase will end up into the combustion chamber, but some of the heat will also be lead direct out of the engine since some of the scavenge gas (fuel/air mix) will be blown out of the engine. This mixture will cool the engine since it is cold due to the evaporation and the rise in gas temp though the engine. This is also one of the reasons why an engine which is running rich is running colder than a lean one... More fuel to evaporate... ritch 4-stroke running which gives less energy produced etc.

Sport_Pilot

I was keeping it simple. I know that they run stoichiometric in the combustors (actually slightly lean of that, except perhaps at the highest power settings), but even with that when they add the extra air it degrades efficiency if not performance. The bypass designs reduce the amount of excess air, but they are still run excess air through the power section, never said they don't. The higher the heat on the turbine blades the higher the efficiency, bleeding air into them degrades efficiency by reducing the temperature, despite running stoichiometric in the combustors. Turbine engines are not efficient enough at low power settings for automobiles. For that they have experimented with turbines with ceramic blades that use no excess air in the power section, though they may through the compressor section to power accessories. This improves efficiency especially at low power.