Where do engines ‘throw oil’ from?

[pinsog]

Many times you will read of non battle damaged engines throwing oil, "My Spitfire began throwing oil and covered my windscreen so I could only see out the side". So where do non battle damaged air cooled engines throw oil from? Where do non battle damaged water cooled engines throw oil from?

The obvious place would seem to be from the exhaust, but it seems to me like the exhaust would be in a location in the slipstream where it wouldn't end up on the windscreen. Also, if it is coming out the exhaust, where is it coming from and why wouldn't it burn before it got out of the exhaust?

 

[FLYBOYJ]

It could be from a number of places. Crankcase seal failure, seal failures at engine accessories, or cylinder head seals.

 

[Crimea_River]

Also prop pitch control can be driven off engine oil.

 

[buffnut453]

In the case of British Leyland engines during the 1970s, the answer was EVERYWHERE!!!

I'll get my coat...

 

[gumbyk]

In the case of British Leyland engines during the 1970s, the answer was EVERYWHERE!!!

I'll get my coat...

There... fixed it for you!

 

[michaelmaltby]

Why did the Douglas Skyraider use so much oil ....? the joke was that its range was limited by how much engine oil it could carry.

 

[gumbyk]

The obvious place would seem to be from the exhaust, but it seems to me like the exhaust would be in a location in the slipstream where it wouldn't end up on the windscreen. Also, if it is coming out the exhaust, where is it coming from and why wouldn't it burn before it got out of the exhaust?

The prop slipstream causes a spiral airflow, so oil coming out the exhaust could end up on the windscreen, say in an upright V-12, depending on which side its coming out. And, these engines all had 'stub' exhausts, and the amount of oil flowing stops combustion. If its coming through the cylinder, the first thing that oil will do is stop the spark plug from firing.

There are also plenty of fittings and accessories that can fail and leak oil. Hot oil is pretty easy to spread around, and you don't need a lot to seriously affect your vision through the windscreen.

 

[buffnut453]

There... fixed it for you!

That's a little harsh. RR turbofans don't appear to leak oil like sieves...at least not the modern ones.

However, liked the speed of your response. Now where did I put that super-sized drip tray....???

 

[pbehn]

I think if any hose or gasket leaks under the engine cover be it oil, petrol or water/glycol by the time it leaks back towards the windscreen it will be black.

 

[mikewint]

As Gumbyk posted "British Engines" Many, Many, years ago I had saved enough money to buy my first Motorcycle. We were out in Indian Country at the time so I wanted a good strong mountain-type bike. A dealer in Chicago was clearancing out last years bikes and had a excellent deal on a TRIUMPH TIGER CUB the "Baby Bonnie" as it was called. Not exactly an off-roader bike but that 200cc engine easily did 60 - 70mph on the road. So off came the fenders and a couple of knobbies and I was King of the Roads and Fields.
After about a month Dad started in on the oil spot the bike was making on the garage floor which was growing every day. Went over every engine bolt and nut but the leak continued.
Finally called the dealer who routed the call to his head British-Imported mechanic. I'll never forget his response "SIR!!! It is a MOTORCYCLE" - Click!

 

[Shortround6]

A number of engines had crankcase "breathers" which sometimes were little more than vents that connected the inside of the crankcase to the outside (although on some car engines the vent was located on valve cover. It still vented either excess pressure inside the crankcase to the outside or allowed outside air to enter the crankcase).
In the 60s with beginning of pollution control the car engines ran a tube from the vent to the intake system and made the engine 'swallow' what oil mist it was creating.

If an engine was running well there might be very little oil being blown out through the breather/s. However, should a piston ring break down or begin to leak the combustion pressure will leak past the piston and pressurize the crankcase. Instead of a sort of give and take as the pistons rise and fall there will be a steady flow of air (or combustion gas) out the vent/s taking oil from the crankcase (oil that leaked from the main bearings, rod bearings and piston pins,etc and got mixed with the air as the crank spun) and this 'airflow' with it's entrained oil is going through the cowl and out the cowl vents.

Yes aircraft engines used oil and it was present in the exhaust but for an engine to start "throwing oil"may mean that something else was going on.

I once had an 1960s Olds F-85 with bad rings, it was using around 1 quart of oil per hundred miles and there was no visible smoke from the tailpipe but the inside of the engine compartment was well rust proofed (especially around the oil filler cap/breather) and there was a visible cloud behind the car.)

In the Med the P-38 photo recon planes had trouble with running out of oil on certain missions. It was discovered that at certain speeds and altitudes the Breathers acted like syphons and sucked the oil out of the crankcase. The fix was simple, they cut the end of the breather tube at a different angle.

Picture of old style oil filler cap for a car/truck.

The metal gauze/screen inside the cap was not going to stop a heavy flow of oil.

 

[MiTasol]

Shortround has covered one of the major causes. Some airframe manufacturers fitted remote breathers (in the belly down near the rudder or in the belly behind the wing) to minimise the problem of windscreen contamination. Engines operating off coranus (crushed coral) will have major breather problems very quickly as the talcum powder fine dust goes straight through the induction system and becomes a fine grinding compound in the cylinders. Other fine dusts do similar damage though a lot slower.

On round engines overtorqued rocker shafts on many engines will produce a sudden leak when the whole top of the rocker box parts company with the rest of the engine. That and gasket failures tend to be caused by improper maintenance (I will just tighten that pivot bolt to stop that small weeping instead of replacing the seals and retorquing to the book value OR that seal face looks clean enough to take the new gasket). Some radial people like to say if its not leaking/bleeding its dead but that is what is politely called bullshoot

On all engines propshaft seals can leak and on hydraulic props the shaft seal can also leak. Some of these leaks are far more likely in dusty conditions.

 

[N4521U]

Crewed a Mustang, D with a Merlin.
1/2hr flight, 1 hour clean-up!

 

[GrauGeist]

Should have seen the Martin Mars...that crate had oil streaks across the top and bottom of the wing that was as black as the night is long...

 

[N4521U]

Brit cars don't need oil changed........!


It gets cycled thru,
never has a chance to get old.

 

[FLYBOYJ]

Many GA aircraft I've flown will throw oil out of the crankcase breather tube. I currently fly a Cessna 172 with an O-320 that will throw oil out if serviced more than 7 quarts (8 is the maximum capacity). I've seen the same thing on some aircraft with O-360s. There's been many theories why this happens, some say the length and the position of the breather tube has something to do with it. It's almost like the engine has a mind of its own and likes a certain oil level.

 

[GrauGeist]

Before the mid-sixties, American automobiles had a crank case breather (typically mounted on the block) that had a "road draft tube".

That tube would drip oil as the vapors would condense on the insides of the tube and of course the oil would get all over the under-carriage.

 

[buffnut453]

Before the mid-sixties, American automobiles had a crank case breather (typically mounted on the block) that had a "road draft tube".

That tube would drip oil as the vapors would condense on the insides of the tube and of course the oil would get all over the under-carriage.

At least it helped prevent rust!

 

[pinsog]

What I am referring to is fighter pilots abusing a single engine fighter during a dogfight and the report reads basically: describes running engine hard/abuse, using max power, maybe water injection, maybe over boosting, over revving etc, and without ever being hit by enemy fire "engine began throwing oil so I broke off and returned to base". So my 'engine throwing oil' question is aimed exclusively at that scenario. Why and where would it start throwing oil from because it was being abused in a combat scenario?

I've been around cars, pickup trucks, semi trucks, farm tractors, bulldozers and assorted heavy equipment all my life so I'm well aware that old engines can and do leak, some have blowby out the vent tube and some leak when new (guy bought a brand new semi truck with a 2 stroke Detroit engine. He was so proud of it he took a picture of it, blew it up, framed it and hung it in his office. 2 weeks later that picture started dripping oil)

 

[mikewint]

The crankcase breather tube could in some older engines act almost like an tailpipe exhaust as exhaust gasses made their way past the piston rings pressurizing the crankcase. Dad had an old beater that he used for work. The exhaust coming out the breather easily equaled the tailpipe. I rigged some old exhaust pipe tubing to direct the fumes under the car
In the cars of my youth one of the major sources of oil leaks was the REAR MAIN BEARING SEAL. and to a lesser extent the Front Main Bearing Seal. They were at the time built like a large thick candle wick and were a bear to get to and to replace. IF you were lucky a special wire hook could be used to snag the old top wick and with traction you could pull out the top seal and then reverse the process to "pull-in" and new seal. A really bad seal could require the dropping of the entire crank.
I would assume that aircraft engines would have something similar??