Where do engines ‘throw oil’ from?

pinsog said:

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?

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Well going back to your OP - the engine IS damaged ( be it "battle damage or not) at that point, again it could be a number pf items.

FLYBOYJ said:

Well going back to your OP - the engine IS damaged ( be it "battle damage or not) at that point, again it could be a number pf items.

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Yes you are correct and all of you gentlemen gave good info about where it could come from. I just wanted to make sure the question was very specific with the circumstances (I'm a little slow but I could figure out oil leaking from a 20mm cannon hole through the block ) which is what I meant by battle damage.

You answer at the beginning was very informative.

Helped with a Beech Stagger Wing, model 17, the owner was having an issue with an oil leak at the front of the engine that looked like the propeller front seal was leaking. The problem was found that an extension had been put onto the engine breather to get the oil/oil mist that did come out the breather to the back of the aircraft instead of covering the belly. This tube was not large enough in diameter, so the crank case pressurized and caused the engine oil to leak out the front of the engine, this was only found after multiple prop seal changes. Once the tube was removed the issue of the oil leak from the front of the engine was corrected. Engine was a P&W Wasp JR, R-985, Propeller Hamilton Standard 2D30.

Most single engine planes had the oil tank mounted on the upper firewall just forward of the cockpit. Any damage to it and it likely blew oil all over the windshield. Damage could be from external sources (guns) or internal (overboosting or engine failure), either of which could cause the tank to fail.

FLYBOYJ said:

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.

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Our CJ-6 is like that, maximum oil level is 11 litres, but we never fill it above 9, or it throws the extra 2 overboard. Its amazing how far 1 litre of hot oil will spread!
Some engines just breathe heavier than others, I guess it may be where accumulated minimum tolerances line up.

On Merlins the first place to look for windshield oil is the prop seal. It is like the front seal on a car engine, where the prop shaft comes out of the reduction gearbox has a seal in there that at high power will push out or wear off enough to weep and leak

Also a lifted head and bank can leak oil out of the gaskets and seals of which I've forgotten the special names but on a TR they are Figure of Eight seals and the head gaskets.

Any ring, cylinder wear, valve seal wear can cause leakage past or above the rings and out the exhaust. This follows the same path as the exhaust path.

On the P-51 the crankcase vent breather is on the right side and can be seen pumping out oil vapor onto the side of the fuselage in many photos both wartime and racing. Long distance Bendix races of the 40's show the most blow-by out of the breather especially visible on Paul Mantz's NX1204 in 1948 as the airplane was in a gray paint scheme and he won at record speed.

Thunderbolt, Hellcat, radial powered bombers, etc, have many leak points due to air and oil cooled design and their engines having more oil use, quantity and therefore usage allowances. The same internal damage to cylinders with piston ring, valve stem seals, or detonation causing lifted cylinders because of stretched cylinder studs can allow lower seal leakage.

Once an engine has used all of its water injection fluid, if left at war emergency power settings it can detonate and cause internal damage. Once power is reduced in this case the lower stresses can allow it to run better, or even smoothly for the rest of the flight with raised temperatures, oil blow-by/through off, as indicators of some wear or damage and after the flight a post flight inspection would determine the failure and course of action for overhaul.

Interesting question, thanks for asking. I like internal combustion reciprocating engines, and have several British cars and an airplane. After 45 years and 30,000 hours flying it still is my thing.

Chris...

Not having a good day.

Radial engines, in particular, throw a LOT of oil, particularly at startup after sitting for a while. It should be obvious, but some of the bottom cylinders are below the oil level in the engine crankcase.

We know that piston rings have a ring gap at the end. Even if the piston has 4 rings (usually one compression ring, one wiper ring, and two oil rings), the oil eventually leaks down through the ring gaps at pools in the combustions chamber. If the chamber fills up, you can actually bend the rods when trying to start it.

Most of the time, either the intake or exhaust valve are open. If the intake is open, oil leaks into the intake track. If the exhaust valve is open, oil leaks out the exhaust pipe onto the ground. If a plane hasn't been sitting too long since running, maybe as long as 4 – 5 hours, the pilot can just crank it up.

The R-2800 technique goes like this, the pilot sets the throttle at a low idle, leaves the mixture in idle cutoff, and turns the starter through 12 blades of the propeller before introducing fuel by cracking the mixture. When the engine fires, it belches a lot of smoke before settling down. The smoke is the oil in the bottom cylinders getting blown out of the intake track and being burned in the cylinders and exhaust stacks. The engine smokes, usually only from the exhaust stack that go to the bottom 1/3 of the cylinders, until the oil in the intake track, the oil in the exhaust stacks, and the oil in the cylinders is blown out or burned up. Then it runs normally.

I've seen an R-2800 in a P-47 that sat for 6 months startup. We decowled it, removed the plugs, turned the prop through 20 blades by hand and got maybe 10 gallons of oil out of it. We then reinstalled the plugs and cowl, and when it started, after turning through another 12 blades, it smoked for about 6 – 8 minutes and blew another 5 – 6 gallons out all over the belly via the exhaust pipe waste-gate.

Also, some radials, the Wright R-2600 in particular, have a wiper ring that is a bit trapezoidal in shape. The ring tapers so the top is a slight bit smaller than the bottom. When it goes up, the oil tends to slip through the slight triangular seal. When it goes down toward the crankcase, the oil gets wiped back into the crankcase. If you don't KNOW that, and if you install the wiper rings upside down, the radial will blow oil like nobody's business.

Here's a clip of our (Planes of Fame, not mine) Curtiss P-47G starting up. Notice he lets 12 blades pass vertical before cracking the mixture.

1. For air cooled engines the hands down favorite oil leak spot is the valve covers. A guy who worked on B-36 ground crews said that it had high voltage vibrators for the ignition, they were mounted on the valve covers, and the result was they always shook the valve cover seals loose. There was an on-going argument among the ground crew as to whether the B-36 used more oil than gasoline.
2. Out the exhaust. Air cooled engines have to have loose tolerances. including in the piston rings.
3. From constant speed propeller seals. The reason that the Hurricane so often is seen with that funny lip on the front of the cowl behind the prop was that the prop leaked oil so much that the had to do something to keep it off the windshield. I have no idea why the Spitfire did not have the same problem.
4. Oil breather overboard vent. If the engine is worn and has combustion gas blowing past the rings it will pressurize the crankcase and blow oil overboard.
5. Loose oil filler cap. We had a local pilot and his wife die from checking the oil when he got to Tampa and not putting the cap back on correctly. He passed any number of suitable airports on the way back when his oil pressure started dropping and failed to make a landing in a nice flat field when his engine quit on final. To make matters worse, he was flying a Cirrus SR-22, with the emergency parachute and did not activate it.
6. By SUPERNATURAL means! None of those problems seem to be true with my Ercoupe but the OIL GETS ON THE COWLING ANYWAY!

pinsog said:

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?

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Think about an engine/propeller engaged in combat: in and out of WEP, diving, climbing, slow, fast, high G, zero G. Constant speed prop and governor working overtime at peak oil pressure to control engine RPM under wildly varying loads and conditions. If there are any weak points or wear spots in the myriad gaskets and seals of this system, this is when they will show up.
Cheers,
Wes

I admit that when I first saw this thread my immediate thought was:-

Anywhere you didn't:-
a) tie down
b) check
c) tighten
d) lock down
e) Think of
f) Anywhere the guy before you didn't
g) tie down
h) Check
I) You get the picture

That oil covered P-47 was based in Italy and had an oil line punctured by an AA shell.

MIflyer said:

The reason that the Hurricane so often is seen with that funny lip on the front of the cowl behind the prop was that the prop leaked oil so much that the had to do something to keep it off the windshield. I

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Did the Brits ever learn to make gaskets and seals that worked? Betcha they were made by Lucas. "Lifetime lubrication and corrosion prevention" gaskets. MGB, TR4, BSA, Gypsy Major, RR Dart, RB211...and the list goes on...drip...drip...drip...!
Cheers,
Wes

N4521U said:

Brit cars don't need oil changed

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Total loss oil system, mate!

Oil cooler matricies failing is also problematic to this day. Our aircraft cleaners cry "Oil cooler change!" when there's a speck of oil on the nacelles. We get prop shaft seals failing, which shows as oil mess around the prop and cowls, also, when ham-fisted engineers miss the funnel when adding oil to the sump it ends up on the lower cowl deck and makes its way out of the aircraft in flight. The worst is hydraulic fluid leaks - 'o' rings in sequencing valves and stuff aren't severe enough to drastically affect quantities or pressure, but they make a shirt of a mess in the undercarriage bays. 3,000 psi of skydrol injecting into the bays when the engines start up and the pumps kick in... blech.

XBe02Drvr said:

and the list goes on...drip...drip...drip...!

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Just like their electrics!

XBe02Drvr said:

Did the Brits ever learn to make gaskets and seals that worked? Betcha they were made by Lucas. "Lifetime lubrication and corrosion prevention" gaskets. MGB, TR4, BSA, Gypsy Major, RR Dart, RB211...and the list goes on...drip...drip...drip...!
Cheers,
Wes

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Mind you, I'm restoring an ambulance with a 202 Holden engine, and lots of oil 'escaping'...

Harley's were exactly oil drip free.

Milosh said:

Harley's were exactly oil drip free.

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Corrosion protection for lower frame tubes. Important in the north country where the road salt from winter doesn't completely wash off til mid summer.
Cheers,
Wes

When the first brand new PBY Catalina flying boat was flown over to the UK by a Consolidated crew, a British reporter present at the arrival remarked, "It certainly did not fly far to get here. There is no oil around the engines."

Sitting down to eat with their guests, the Brits asked the crew what route they took to get there. They told them. The Brit response was silence. It would have been impolite in the extreme to call their guests bald faced liars. No British aircraft could have flown that route. Then they asked about the radio. The ferry crew responded that they had been communicating with San Diego while on final approach; this produced still more disbelief. They went up in the PBY the next day, communicated again with San Diego, and the Brits began to realize the Americans were not liars. The airplane really could fly that far, the radio really had the range to reach the other side of the US, and the engines did not leak copious amounts of oil.

When the first models of the Sunderland flying boat were equipped with US made engines the crews marveled at the fact that they could fly a lengthy patrol and actually come home with all four engines still running.

By the way, the jet engines used in the YB-49 flying wing did not have full oil recovery. The aftmost bearings had no oil return and the oil was allowed to flow out into the exhaust. Filling the oil tanks before flight was an essential task, which was not accomplished before the airplane left for return to Muroc following its demonstration flight to Wash DC. They ran out of oil and had to make an emergency landing in Arizona.