Normal oil consumption?

[low-n-slow]

Curious what the general opinion is on how much oil a C85-12 engine should use? engine has 850 smoh, just came out of annual with compressions at 78, 78, 76, 76, oil pressure is good, temp stays good, engine runs very strong and smooth.... Only issue is we go thru a quart of oil every two hours. Usually fill to four quarts and at a quart when it gets down to 3 on the dipstick. Any and all suggestions would be greatly appreciated!

[Nathan K. Hammond]

Jon,

Most Continental's will puke that first quart out when filled to the brim. It's just the nature of the beast. On my C85/O200 it would slobber oil until it got down to about 3-1/2 quarts. So I would let it drop down to 3, then add half a quart. When I had the A65, it didn't like anything more than 3 quarts and over the span of 25 hours wouldn't lose more than a 1/4 quart.

Next time, wait until it gets down to about 3 quarts on the stick and see if it doesn't dry up. These little engines will run fine with less than a quart in the tank. THAT DOESN"T MEAN I'd do it, but to illustrate the point; a full 4 quarts isn't necessary.

nkh

[Carl Prather]

You might look at this link: http://150cessna.tripod.com/c150o200ainsp.html
It shows a breather tube modification sold by Cessna that reduces crankcase blow by. Many airplanes just won't hold the last quart of oil and dump it overboard in short order. To start, you might just want to run your engine one quart low to start if the operating manual says it's OK and see if this helps.

[Mnflyer]

Hi Jon, as Nathan & Carl posted the 1st qt goes pretty fast, my 0-200 goes thur a qt every 3 hrs, a lot of it out the breather, I did the breather mod. and it definitely helped I'd say there is about 1/3 the oil that drips out on the catch pan in the hangar after a flt now.

[low-n-slow]

One other tidbit.. it does not drip oil on the floor of the hangar, anything that it leaks ends up on the belly. At least the belly won't rust we will run it at 3 quarts and see if stabilizes.... If the oil level continues to drop at a rate of one quart per every two hours, should we be concerned or just keep adding oil?

Thanks for the advice

[MikeB]

Jon, At any rate, a quart every two hours does seem excessive and as others have suggested, running it a quart low may 'solve' the problem.

On the other hand: I've never understood with all the technology available why it's acceptable in aircraft engines to use a quart in even four or six hours just because you fill it to the "full" level. I do understand that clearances are greater, but so are they on my air cooled lawn mower which I can run a whole season (and I mow over an acre) and never have to add for the whole season. I rebuilt the engine on our airport mower
(twin cylinder Kohler, five foot deck) about 8 years ago and have never added more than part of a quart for the whole season (but enough of a rant.......... )

Although low cylinder leakages of 77/80 etc. may be an indication of good cylinder components, it basically is a check of the compression rings/contact and valve seating. In other words, the oil rings could be worn or the drain back holes plugged and it's possible the cylinders could still read at an acceptable level. This may spark a discussion, but it's been my experience over the past 40 some years. I've always had a bit of a problem with the cylinder leakage test anyway as (1) your piston is only in that position (TDC) for a millisecond when the engine is running at speed and (2) input air of 80 psi really doesn't duplicate running engine firing/cylinder pressures as compression rings get a great part of their seating ability from gas pressures pushing behind the rings, along with a large free diameter. However, it's the industry standard and we're stuck with it ........(another rant).

Do you possibly have chrome cylinders by any chance? It's not unusual for engines with chrome cylinders to use more oil than those with standard steel, etc.

BTW: the Lycoming in my old Cherokee 140 seemed to toss the first two quarts so I had to run it between 6 and 7 quarts (held 8 ). After which it used very little oil (maybe a quart) in 20 hours. The A65 in my Champ seems to settle down around 3-3 1/2 quarts to about a quart in 8-10 hours.
I've never let it get much below 3 quarts as it raises the pucker factor over any distance.

Good luck and hope you find your problem! Let us know!

Mike Berg

[big chief 48]

here is my two cents worth... When my 85 was majored the first time (2001) It used a quart every 1-2 hours. This went on for 70-80 hours and was getting me ticked off. And yes I was only filling it 3 and a half. At 125 hours, my case started "fretting" and the engine started to get tight, like the prop would turn like it was 20 below zero. So we sent it out to get line bored and started over from scratch. My engine now has 370 hours on it and does not use more then a quart every 6-8 hours. Why the difference? 1. If you have chrome bores and they do not seat, you will dump/burn oil. The way to help eliminate this problem is to run them in real hard. With my first engine, I putted around the airport thinking a nice gentle break in would help. I found out this is dead wrong. As soon as there a are no oil leaks, take the plane up and put the power to it (within rpm limits) to help seal the piston rings up against the cylinder walls. The only way you get rid of blow by is to get the rings seated and that can take some time, effort and luck. I've been told by some old timers that they would have to try 3-4 times to get s a stubborn cylinder to seat. Good luck!!

[low-n-slow]

one cylinder was replaced last fall as the compression on that cylinder went south. Could it be using oil as it still seating the rings on that cylinder? As far as I know, none of the cylinders are chromed.

[MikeB]

Jon,
If it has chrome, the cylinders should be painted orange on the bottom.
Don't know how many hours you have on the new cylinder, but sometimes they take 50 hours or so to seat and they have been known to get glazed rather than 'break in'. Especially if the engine temperature has ran on the cold side during the break in process (see "Big Chief above). Usually on the cylinder (s) pumping oil the spark plugs will be oily and you can also pull the plugs, run the piston to the top and shine a 'bend a light" into the cylinder to check for oily pistons which is also an indication of oil pumping. Or a borescope is even better.

I think I'd try the one quart low trick first, though. Anyway, try everything on a systematic approach. Many engines have been overhauled for no good reason because it was misdiagnosed .

Mike Berg

[Roger Anderson]

Had a 7DC with a C85. From major until sold several hundred hrs later, was consistant at 1 qt each 5 hrs. Was a great engine. My A65 however was a quart each 6-7 hrs right after TOH, slowly increasing to 1 qt every 20 hrs, 500 hrs later. A qt. every 2 is a lot. roger

[Tim Juhl]

With my C85-12 and chrome cylinders I'm using 1 qt every 5 hours or so at 200 hours SMOH. The initial oil consumption for the first 100 hours was usually not that good. If I were to do it over again I don't think that I would put chrome cylinders on this small an engine. They worked fine on my Lyc 0-320 and Cont 0-470 but are much harder to break in on the small continentals. During the first 50 hours I typically ran at 2400 rpm and I still don't baby the engine.

In trying to reduce the oil consumption I installed the extended "aerobat" type crankase vent elbow and route the vent hose up and over the engine to a M-20 type air/oil separator. No drips on the hangar floor anymore but it still uses some oil. I usually keep my oil between 3 and 3.5, filling to 4 qts if I'm going any distance. I find I get lower oil consumption using straight weight (shell W-100+ and etc.) than I do with multigrade oils (tried both shell and Exxon.) I usually run straight weight in the summer, multi in the winter.

Engine runs strong, has good compression, tends to run a little on the cool side (oil temp) in cold weather, 170-190 in the summer.

Tim Juhl