Disclaimer: We have no professional or expert qualifications of any kind.
It's fully up to you to check any information you find here with
standard aviation industry sources such as aircraft maintenance
manuals, flying instruction books and, above all, FAA regulations!


Click on the picture for high-resolution image

By Ed

I've have seen people use the hose that goes up and over the cylinders, then down, behind the engine, to the bottom of cowl. This causes the first part of the hose to be uphill. That may help some.

I've seen people install an oil/air separator and that can help some.

If one of those is enough, that's nice.

I've seen oil come out of a Coupe O-200 engine installation so fast that caused a forced/precautionary landing in a field (successful) because of loss of oil pressure. It may be that the O-200 splashes oil more vigerously inside the crankcase.

This last instance was ONLY solved by adding the breather-elbow extension. The extension is a tube that gets soldered (silver-solder?) to the crankcase side of the breather-elbow and acts as a pipe sticking a certain fraction of an inch inside the crank-case.

The breather-elbow extension works, it seems, because oil is splashed around the inside of the crankcase. Since there's always air-flow out the breather, it'll suck oil from the case walls right along with the air. The extension makes the inlet suck air that's not right along the crankcase wall. The oil on the walls seems not to go along. This seems to put a firm and immediate stop to the oil/breather-tube problem.

I think I heard this elbow extension was a standard part on a later Coupe engine (?C-90?) for a while. It can be fabricated by someone with proper skill. I would make very xxxxx sure the mechanic attaching the extension knows what he's doing since I wouldn't want even a short aluminum tube bouncing around inside my engine. I have seen one instance (cited above) where this was the only thing that made much difference to the problem and this solved it completely. I heard of some other instances where this solve the person's problem.

Again, I ain't a mechanic and my memories of this are 8-10 years old. Is there someone out there who can give exact and specific info on how to buy/fabricate a breather-elbow extension?

Here's info from John at Skyport
P.O. Box 249, Rensselaerville, NY 12147
800 624-5312

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 artificially high. The second reading is the correct one.

Oil Fill level and blow out from the breather tube
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 anecdotal 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.  Putting a home brew oil trap on the blowby tube can be problematic, regardless of the legalities. If, for example, it freezes up, you can blow a seal and loose a lot of oil in short order. Better to get it working correctly, and if you're still dissatisfied, add an approved separator.

Better to correct the problem than put expensive lipstick on a bulldog. And end up with bulldog teeth marks on your butt