Oil Consumption and Breather Tube

[ColoRv]

Just another data point. I still have the vacuum system in place, though I intend to remove it when I go full inverted systems (after Oshkosh). I recently flew from Denver to the Florida keys and spent a week flying around Florida. 25 hours of flight time total. Here is a pic of the vacuum tube following the flight.



I don't know why some installs are coking up and others are not. Perhaps it is how the planes are flown, perhaps it's the oil used, condition of the engine....I have no idea but as you can see, mine shows just about zero buildup in the 25 hours of flight, many of which were long legs (9.5 hr day returning into headwinds). I do still treat this as an untested experimental setup sold with zero pre-testing and questionable engineering....meaning I look at it often. I also scrapped the valve Alan sent and used a Napa.

[Gash]

Thanks for the pic. Please tell us how you run your engine. LOP? ROP? What kind of EGT are you seeing typically on that exhaust pipe while in cruise? How many inches from the end of the pipe did you install the stem? What type of oil do you use, and finally, what engine are you running? Thanks for much for adding to the data collection!

[BillL]

Originally Posted by Gash

Thanks for the pic. Please tell us how you run your engine. LOP? ROP? What kind of EGT are you seeing typically on that exhaust pipe while in cruise? How many inches from the end of the pipe did you install the stem? What type of oil do you use, and finally, what engine are you running? Thanks for much for adding to the data collection!

Additional question - - how long from start to shutdown - especially in cold weather. The theory under thought is water laden blowby, where several cycles have not evaporated all the collected moisture from the oil. Then the condensed water in the cold pipe collects and carries oil to the evaporation/collection point, then with time it hardens and restricts. Just a hypothesis separate from steady state conditions.

[ColoRv]

Originally Posted by Gash

Thanks for the pic. Please tell us how you run your engine. LOP? ROP? What kind of EGT are you seeing typically on that exhaust pipe while in cruise? How many inches from the end of the pipe did you install the stem? What type of oil do you use, and finally, what engine are you running? Thanks for much for adding to the data collection!

I operate almost exclusively at 100 ROP.
EGT's typically between 1200 and 1275 in cruise
Vacuum tap is 13 inches from #4 flange. Closer to the heat than some have installed theirs I think. Vetterman 4 pipe system
I use Aeroshell W80 plus in winter W100 plus in summer
Engine is Angle Valve 360, 10:1 pistons, dual Pmags, Superior cold air sump

As for how I operate the engine.... I seldom fly for less than 45 minutes winter or summer, and oil temps always over 170 (using shudder in winter). Throttle spends far more time full forward than in any other position, RPMs between 2300 and 2600 depending on my mood and how quickly I want to be there. Gentlemen aerobatics are common. Down in Florida I did find I seldom had the throttle full forward because I was always flirting with over speed. Sea level...what a beast she is down there. When going below 5000 here at home requires a shovel...no such issues....shove it forward.

I hope that helps some of the brighter minds figure out why some systems coke up while others do not. I have found traces of coking during previous checks but never more than is seen in the picture I posted previously. I will keep checking though.

Alan, have you considered a coating for the inside of these pipes? Something more difficult to stick to?

[PerfTech]

I hope that helps some of the brighter minds figure out why some systems coke up while others do not. I have found traces of coking during previous checks but never more than is seen in the picture I posted previously. I will keep checking though.

Alan, have you considered a coating for the inside of these pipes? Something more difficult to stick to?

.... Every time we were contacted by someone that had above average coking of their unit we would ask them to participate in our testing program. We sent out for testing an array of different designs and variations. We did try some tubing that had a coating similar to that found on frying pans Etc. Some with longer, shorter, different diameters, vented for cooling, an insulator gasket between the saddle and exhaust pipe and a few others. Now that we have gathered a considerable amount of information, with lots of hours on each design change, and having spent many hours poring over the collected data, I can finely report our findings. The one thing we saw consistently was this, the aircraft with the highest oil consumption seemed to have the worst accumulations. We did see minor changes with the different designs and mounting locations, but nothing dramatic, and definitely not a significantly different result. Unfortunately we weren't successful in finding a 100% cure and we will continue our testing program. We did learn one thing for sure, if the tube into the exhaust is checked / cleaned at oil changes you should never have a problem. We also have available on our website an inexpensive, easily installed, small safety bypass kit (we recommend installing this on all vacuum systems) that eliminates any and all possibility of a problem from coking, a failed valve or any breather restriction problems. In defense of these vacuum systems, we must add that the coking has occurred on a vary small number, (a fraction of 1%) considering the quantity (several thousand) in service. Thanks, Allan

[hydroguy2]

FYI...I've been running Allens oil separator in conjunction with a Napa 2-29000 valve for about 1.5 years and a 150hrs. I inspect at oil changes and never had any build up....until this year. There was coked oil, but still had a 1/8" or so hole. Also, I don't have a overpressure relief valve installed. BUT........

I pulled the valve and blew thru it like always and this time it seemed to have some resistance. I wondered if it was my imagination or just memory loss. Anyway I talked with Stephen C about his set-up. He said why bother worrying, $18 bucks put a new one on.

Got 2 new ones and they are much easier to pass air through. My old valve was getting stiff and reluctant to move. So new valve and added the over pressure relief valve like many others have done.

so this years Condition Inspection Lesson: Just because things have been working good, they still need some thinking to ensure they stay good.

[Bill.Peyton]

I would never run the valve into the exhaust without a bypass safety valve. It's just not worth the downside. We have had two reports of blown front seals resulting in inflight emergencies. I had the valve installed and after 50 hours it was 75% blocked. It's now back to just venting on the belly. My oil consumption is a quart every 18 hours.

[BillL]

Originally Posted by Bill.Peyton

I would never run the valve into the exhaust without a bypass safety valve. It's just not worth the downside. We have had two reports of blown front seals resulting in inflight emergencies. I had the valve installed and after 50 hours it was 75% blocked. It's now back to just venting on the belly. My oil consumption is a quart every 18 hours.

Yes, Bill, and people should not let the 1% failure fool them. It will coke, it truly is just a matter of time if left unattended. Proper maintenance should eliminate nearly all possibility.

50% of RVers fly less than 100 hrs/yr according to those who answered the survey.

[flightlogic]

Edit...
Thanks Bill.... looking closely at the slant cut tube... it appears it is facing correctly.
Still searching for my extra horsepower... have yet to find it.

[Bill.Peyton]

The slash cut opening is should be facing towards the rear of the aircraft to create lower pressure. See post 21