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John, Thank you. This explanation makes sense and seems consistent with my experience. I was not aware that the oil filler tube was below the level of the oil. The oil filler cap on my plane is very tightly sealed (air tight). The 6 quart maximum is a joke, since a full quart of that seems to blow out of the engine onto the belly & side of the plane within an hour or two. AT 5 quarts & below the oil level is very stable. I wouldn't ever try running the O-200 below 3.5 to 4 quarts however it's reassuring to know that the engine can run safely on 3 quarts. I have a vented aluminum catch tank at the end of the breather line. It keeps most of the oil off of the bottom of the plane, particularly if someone over fills the engine. My O-200 only loses about 1 quart every 15 to 20 hours (1100 SMOH), once at or below 5 quarts. Compression on all cylinders runs in the between 74 & 78 PSI. No bulldog bites on my butt yet, & hope to keep it that way! Dan N3968H ----- Original Message ----- From: <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]>; <[email protected]> Sent: Saturday, February 14, 2004 10:59 AM Subject: Re: [COUPERS-FLYIN] Dirty Belly - Oil level mystery > ----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]---- > > > First, the dip stick mystery. > > The tube the dip stick is in is generally below the level of the oil in the > tank. The dip stick cap seals the top of the tube. So, when you shut down the > engine, you have a sealed tube containing warm air in the top, the bottom of > which is submerged in oil. As the trapped air cools it contracts (a lot more > than the hot oil would) and draws oil up into the tube. When you open the cap > the oil drops back down into the tank, seaking its own level, but the reading > on the stick is artifically high. The second reading is the correct one. > > 4-5 quarts is enough unless you experience engine cooling problems, which you > shouldn't. The 6 qt requirement is arrived at by virtue of a certification > requirement: The engine must be able to run without exceeding its maximum > allowed oil temperature with half of the specified oil level, thus 3 quarts is > enough and 6 is what they mark the capacity at. This is why there is a slight > difference between the C75, C85 and C90 oil "capacities". Same tank, just > different markings. > > All C-series Continentals, including the O200 have a dry sump, so, > theoretically, any oil level that is contained entirely within the tank should be OK. > Lycomings blow oil when the level is too high by virtue of the fact that the > crankshaft beats the oil around. This should not happen on the C-series. > Regardless, there is anticdotal evidence that higher oil levels result in more oil > out the blowby tube. Go figure. > > There are a number of oft overlooked causes for oil out the blowby tube. > Here are some in no particular order: > - Leaking crankshaft seal allowing ram air to pressurize the crankcase. > - Excessive blowby pressurizing the crank case. > - Blowby tube incorrectly positioned, resulting in a low pressure in the tube > - Missing extension on the crankcase vent elbow, especially on engines with > accessories on the nose (vacuum pump, fuel pump, injection pump). > > An oil separator should not be necessary, unless you're trying to keep a show > quality plane spotless. If you've got excessive oil on the belly after a > couple of hours, something is wrong. Better to correct the problem than put > expensive lipstick on a bulldog. And end up with bulldog teeth marks on your butt > later... > > John > ========================================================================== == == > To leave this forum go to: http://ercoupers.com/lists.htm > Search the archives on http://escribe.com/aviation/coupers/ > > > ========================================================================== ==== To leave this forum go to: http://ercoupers.com/lists.htm Search the archives on http://escribe.com/aviation/coupers/
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