Frozen Crankcase Breather

April 1993

The following experience is reiterated in the hope that reading about it may prevent a similar problem, or at least allow someone unfortunate enough to run into this, to come through it undamaged.

Sally and I flew our Long-EZ to Telluride, Colorado this past February. We had planned five days of skiing in the San Juan mountains. We landed at Telluride airport which is at 9100 feet elevation. There was lots of snow and it was cold, especially at night. There was no hangar or tiedown available so we parked nose down, into the wind.

While we were there, it snowed four to six inches each night. The last night, we had 27 inches of snow. We had to dig the Long-EZ out of the snow before we could leave.

A careful preflight was conducted, followed by pulling the prop through enough times to show oil pressure on our mechanical gauge. The engine started easily and I warmed it up at low power. did not taxi out for take-off until I had 120OF oil temperature. We took off and headed directly toward Page, Arizona at 14500 feet.

One hour out of Telluride, I suddenly noticed the oil pressure gauge fluctuating. The oil pressure slowly fell from 85 to 60psi. At this point, I hit the Loran "nearest airport" button and headed for the brand new Black Memorial airport near the northeast end of Lake Powell.

We removed the cowl and found that the engine had only 1-1/2 quarts of oil left in the sump. We had left Telluride an hour earlier with 7-1/2 quarts! There was evidence of oil near the push rod tube seals, the rocker cover oil drains, but no oil in the vicinity of the main bearing/prop seal. The prop had some oil on it, but not nearly as much as I would have expected considering we had lost 6 quarts of oil!

We topped off the oil, ran the engine for 10 minutes with no sign of an oil leak. We replaced the cowling and headed toward Mojave. One hour later, we had an exact repeat of the problem! This time, we landed at Boulder City, Nevada. It Was much warmer there. We went through essentially the same steps again; filled up the oil, replace the cowl and headed for home. One hour and minutes later, we landed at Mojave and found that we had not used a perceptible amount of oil!!!

Here is my theory but, I hasten to add that I have no conclusive proof of anything at all. We have one of Wes Gardner's breather systems installed and we have run this system for more than 1500 hours without a problem. For those who may not be familiar with this system, it consists of a 5/8" I.D. hose that runs from the crankcase breather elbow to an anti-backfire valve welded into the exhaust system. There is a "T" fitting in this hose from which a 3/8" I.D. hose runs to an automotive PCV valve, and then to the intake manifold (in my case, a fitting is screwed into the Ellison throttle body in the venturi). At low power, the anti-backfire valve does not open and the crankcase breathes through the PCV valve and into the carburetor, then into the cylinders where the crankcase gases are burned in the cylinders and go out the exhaust. At higher power, the PCV valve closes and the anti-backfire valve opens. The breather gases flow directly into the exhaust system, are burned and expelled through the pi-op.

I later found that the anti-backfire valve had carboned up to about 80% blocked. I believe that the moisture, normally expelled from the breather, froze in the partially carboned and blocked anti-backfire valve. With the very low temperatures at Telluride, particularly at night, this moisture froze hard. Even though I warmed the engine until the oil temperature read 1200F, this did not help because the breather system is located entirely on the "cold" side of the engine baffles. This means the cold air being pulled through the cowling during the engine warm-up

kept the frozen breather frozen. The flight at 14500 feet (minus 200C) continued to keep the breather frozen.

With the normal crankcase vent (the antibackfire valve) plugged, crankcase pressure built up and began to force oil out of the seals, as well as through the PCV valve, into the carburetor, up through the manifold and into the cylinders where it was burned and expelled out of the exhaust. I believe this continued at a rate of 6 quarts per hour, or 0.1 quarts per minute. In other words, the engine burned most of the oil while some of it leaked out of the seals. The small amount of oil found on the prop, on the engine and in the cowling supports this theory although, to be honest, not everyone agrees with this hypothesis.

The temperature at Black Memorial airport was cold enough so that the frozen blockage did not melt. The temperature at Boulder City was in the low 80's - this finally melted the frozen breather ice and so we did not use any oil from Boulder City to Mojave.

I replaced every part of the breather system, new hoses, new PCV valve, new anti-backfire valve. I did not find anything wrong with the original parts, for what that is worth. I ran a 3/8" drill through the carboned up anti-backfire valve mounting and was surprised at the amount of carbon that came out. In the 40 hours flown since this incident, oil consumption has been normal (about 1 quart per 14 hours).

I intend to keep on using Wes Gardner's breather system. It has given excellent service for hundreds of hours. I will, however, do two things differently from now on. I will check the carbon build-up and clean it out every 100 hours and, I will pre-heat the engine compartment before starting it if it has been left out, overnight, in sub-zero weather. I would recommend that anyone using this breather system do the same thing.

I would value any and all opinions about this incident. Has anyone else out there has anything like this happen to them?

Mike Melvill

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