M00N37 Posted September 8, 2019 Report Share Posted September 8, 2019 I have been having mysterious oil leak problem. Today I flew 4 flights. First two flights were flown at 12,000ft with 16" at 2500RPM and I got the usual but more than normal of oil dripping from air box drain tube. 3rd flight was when thing got interesting. I took off with 6.75qt of oil. Flew for about 90 minutes at 7,000ft with 16" at 2500RPM. About 20 minutes from destination, my oil pressure was in the yellow. Oil level when landed was at 4qt. There was oil dripping out of the air box drain tube. It was a drop every second. I assume that is where most of the oil went. Last flight of the day was flown at 8,000 with full throttle and 2500RPM. At shutdown, there was no oil dripping out of the air box drain tube at all and oil level only drop from 8qt to 7.75qt. Is it normal for oil to be suck out of the engine when flying at low MP ? I'm experimenting with going slowly and burn as little fuel as possible. 16" at 2500RPM still gives me about 105kts TAS at 6-7GPH. Quote Link to comment Share on other sites More sharing options...
Skates97 Posted September 8, 2019 Report Share Posted September 8, 2019 Fill in some info in your avatar like what model you are flying. It will help to know what engine you are behind. Some with more knowledge than I will be along soon. Not to knock what you are doing looking for low fuel burn, but why fly at 105kts? I didn't buy my Mooney to go slow, I bought it because it takes me along at about 140kts IAS on about 9.5+ gph, the O360 won't really run lean of peak. Even so, I feel like for the speed that I'm flying the fuel flow is very economical. The sweet spot for my NA engine seems to be between 8-10,000'. Depending on winds and temps (hot out west in the summer) I am typically at 8,500, 9,500, or 10,500. Quote Link to comment Share on other sites More sharing options...
M00N37 Posted September 8, 2019 Author Report Share Posted September 8, 2019 21 minutes ago, Skates97 said: Fill in some info in your avatar like what model you are flying. It will help to know what engine you are behind. Some with more knowledge than I will be along soon. Not to knock what you are doing looking for low fuel burn, but why fly at 105kts? I didn't buy my Mooney to go slow, I bought it because it takes me along at about 140kts IAS on about 9.5+ gph, the O360 won't really run lean of peak. Even so, I feel like for the speed that I'm flying the fuel flow is very economical. The sweet spot for my NA engine seems to be between 8-10,000'. Depending on winds and temps (hot out west in the summer) I am typically at 8,500, 9,500, or 10,500. The engine is O-360-A1D in M20C. Sometimes the weather is moving slower or worse than expected and I won't be able to land when I get there at normal speed, so no point in going fast and hold. Other times I just wanna stay in the air as long as possible. Quote Link to comment Share on other sites More sharing options...
ArtVandelay Posted September 8, 2019 Report Share Posted September 8, 2019 Lycoming 360s like to be filled to 6 quarts, any more than that they blow out, but it should stabilize at 6? Tom 1 Quote Link to comment Share on other sites More sharing options...
Shadrach Posted September 8, 2019 Report Share Posted September 8, 2019 (edited) 9 hours ago, M00N37 said: I have been having mysterious oil leak problem. Today I flew 4 flights. First two flights were flown at 12,000ft with 16" at 2500RPM and I got the usual but more than normal of oil dripping from air box drain tube. 3rd flight was when thing got interesting. I took off with 6.75qt of oil. Flew for about 90 minutes at 7,000ft with 16" at 2500RPM. About 20 minutes from destination, my oil pressure was in the yellow. Oil level when landed was at 4qt. There was oil dripping out of the air box drain tube. It was a drop every second. I assume that is where most of the oil went. Last flight of the day was flown at 8,000 with full throttle and 2500RPM. At shutdown, there was no oil dripping out of the air box drain tube at all and oil level only drop from 8qt to 7.75qt. Is it normal for oil to be suck out of the engine when flying at low MP ? I'm experimenting with going slowly and burn as little fuel as possible. 16" at 2500RPM still gives me about 105kts TAS at 6-7GPH. I am assuming you are running at very reduced throttle positions. If so, the higher vacuum level with the engine throttled back generates high differential pressure (suction) across the intake valve guides. This can siphon oil into the intake manifold from the cylinder head. The oil then migrates down the intake tubes. The oil will eventually make its out of the air box via the drain tube. With the throttle wide open you’d likely not see the problem. Given how much oil it’s siphoning, I suspect you may have a leaky intake valve guide(s). Edited September 8, 2019 by Shadrach 2 1 Quote Link to comment Share on other sites More sharing options...
takair Posted September 8, 2019 Report Share Posted September 8, 2019 I assume you are describing the oil coming out of the sniffle valve? You may have one or more sloppy intake valves that let oil by the stem. This is likely made worse at low manifold pressure. The way to confirm would be to pull intake tubes to inspect. Not sure there is any limit, unless you do a valve wobble test. The fix is likely new valve guides. Less likely, be sure your oil return lines from the head are not plugged. 2 Quote Link to comment Share on other sites More sharing options...
M00N37 Posted September 8, 2019 Author Report Share Posted September 8, 2019 1 hour ago, Shadrach said: I am assuming you are running at very reduced throttle positions. If so, the higher vacuum level with the engine throttled back generates high differential pressure (suction) across the intake valve guides. This can siphon oil into the intake manifold from the cylinder head. The oil then migrates down the intake tubes. The oil will eventually make its out of the air box via the drain tube. With the throttle wide open you’d likely not see the problem. Given how much oil it’s siphoning, I suspect you may have a leaky intake valve guide(s). 1 hour ago, takair said: I assume you are describing the oil coming out of the sniffle valve? You may have one or more sloppy intake valves that let oil by the stem. This is likely made worse at low manifold pressure. The way to confirm would be to pull intake tubes to inspect. Not sure there is any limit, unless you do a valve wobble test. The fix is likely new valve guides. Less likely, be sure your oil return lines from the head are not plugged. I recently had 2 cylinders deglazed and 2 are brand new. Would the problematic cylinder also have oily bottom spark plug ? Quote Link to comment Share on other sites More sharing options...
takair Posted September 8, 2019 Report Share Posted September 8, 2019 1 minute ago, M00N37 said: I recently had 2 cylinders deglazed and 2 are brand new. Would the problematic cylinder also have oily bottom spark plug ? Maybe not. I have one that has a similar dribble, but plugs are relatively clean. It just drools down the valve into the intake manifold. Mine does not sound as bad as yours, but I typically fly lower and higher power. On borescope I can tell that there is a little more oil burn than the other jugs. I have a spare on order to replace it at next opportunity. 1 Quote Link to comment Share on other sites More sharing options...
Yetti Posted September 8, 2019 Report Share Posted September 8, 2019 (edited) 1 hour ago, M00N37 said: I recently had 2 cylinders deglazed and 2 are brand new. Would the problematic cylinder also have oily bottom spark plug ? So first thing.... where the oil comes out, is not always the source. Wind comes in the front and then blows the oil around at 200 mph. Sounds like an oil control ring may be broke or stuck on #2. Find the source of the leak is the first step. open it up and get a flashlight and spend some quality time with your plane. Edited September 8, 2019 by Yetti Quote Link to comment Share on other sites More sharing options...
carusoam Posted September 8, 2019 Report Share Posted September 8, 2019 M20Cs don’t leak oil at altitude any more than they do at low altitudes... normally. expect something isn’t working right... Low power and low rpm doesn’t usually have high case pressures... or cause oil challenges They do get the oil pushed out the case vent... when over filled. PP thoughts only, not a mechanic. Best regards, -a- Quote Link to comment Share on other sites More sharing options...
takair Posted September 8, 2019 Report Share Posted September 8, 2019 44 minutes ago, carusoam said: M20Cs don’t leak oil at altitude any more than they do at low altitudes... normally. expect something isn’t working right... Low power and low rpm doesn’t usually have high case pressures... or cause oil challenges They do get the oil pushed out the case vent... when over filled. PP thoughts only, not a mechanic. Best regards, -a- If it is coming out of the sniffle valve, at low manifold pressure (perhaps not so much the altitude), I think this yields higher differential pressure between the rocker box and the intake manifold. If the valve guide is sloppy, it can draw some oil with it, through the intake valve. Some will get burned with combustion, but some can end up in the intake plenum. It puddles until the sniffle valve opens and then drips out......that’s my theory anyway. Could be off my “rocker”. 1 Quote Link to comment Share on other sites More sharing options...
M00N37 Posted September 9, 2019 Author Report Share Posted September 9, 2019 I did multiple test flights today to confirm my hypothesis. The engine likes oil at 6qt. Anything over 6 seems to get blown out. As for the power setting, I saw no oil loss when cruising at full throttle. However I lost almost 2 qt in just 30 minutes by cruising at 3000ft with 17” 2500RPM. Apart from valve guide, clogged drain back tube, and oil control ring. Anything else that could be causing this ? Quote Link to comment Share on other sites More sharing options...
takair Posted September 9, 2019 Report Share Posted September 9, 2019 13 minutes ago, M00N37 said: I did multiple test flights today to confirm my hypothesis. The engine likes oil at 6qt. Anything over 6 seems to get blown out. As for the power setting, I saw no oil loss when cruising at full throttle. However I lost almost 2 qt in just 30 minutes by cruising at 3000ft with 17” 2500RPM. Apart from valve guide, clogged drain back tube, and oil control ring. Anything else that could be causing this ? That is significant, I missed the significant amount earlier. There is also the possibility of a cracked jug....not sure I can explain it, but 2qts in 30 minutes is serious. Suggest you have your mechanic start with compressions and borescope. Quote Link to comment Share on other sites More sharing options...
takair Posted September 9, 2019 Report Share Posted September 9, 2019 Thinking about it more. Someone mentioned rings, with less cylinder pressure the rings may not seal as well. Not sure why you would get more oil out the air box that way, but I think you need to sort this out on the ground, could also be a combination of things. Quote Link to comment Share on other sites More sharing options...
Shadrach Posted September 9, 2019 Report Share Posted September 9, 2019 16 minutes ago, M00N37 said: I did multiple test flights today to confirm my hypothesis. The engine likes oil at 6qt. Anything over 6 seems to get blown out. As for the power setting, I saw no oil loss when cruising at full throttle. However I lost almost 2 qt in just 30 minutes by cruising at 3000ft with 17” 2500RPM. Apart from valve guide, clogged drain back tube, and oil control ring. Anything else that could be causing this ? 2qts in 30 mins at any throttle position is unairworthy in my book. 1 Quote Link to comment Share on other sites More sharing options...
M00N37 Posted September 9, 2019 Author Report Share Posted September 9, 2019 48 minutes ago, takair said: Thinking about it more. Someone mentioned rings, with less cylinder pressure the rings may not seal as well. Not sure why you would get more oil out the air box that way, but I think you need to sort this out on the ground, could also be a combination of things. If this is the case, would the compression test even matter ? Since the MP is way less than ambient, the pressure is the other way around. I'm gonna have a mechanic pull the valve cover first to see if there is any excess oil caused by clogged drain back tube. Quote Link to comment Share on other sites More sharing options...
takair Posted September 9, 2019 Report Share Posted September 9, 2019 15 minutes ago, M00N37 said: If this is the case, would the compression test even matter ? Since the MP is way less than ambient, the pressure is the other way around. I'm gonna have a mechanic pull the valve cover first to see if there is any excess oil caused by clogged drain back tube. Was just thinking you may be pushing oil past the rings to the combustion area. If it is a significant amount, it could then get past the intake valve, but usually you would have spark plug fouling. Compression check is quick and easy way to tell gross cylinder health....so almost free if they are re already in there. Quote Link to comment Share on other sites More sharing options...
carusoam Posted September 9, 2019 Report Share Posted September 9, 2019 Wait a minute... Come on Moon... time to write some details... show some pics... You have an M20C? Or G... You have an O360... So there is no sniffle valve? You have an air box... I don’t know what you are referring to here, it would be a guess why it leaks oil... Show some pics... This can help get you going in the right direction... The oil is leaving the engine. Identify the spot(s) it is leaving through... Blocked oil return lines aren’t making oil go away... how would a return line get blocked? Open oil return lines would make an impressive mess... No need to fly a plane that is running out of oil at a high rate... No need to fly a plane to experiment with oil loss... No need to guess... If oil is escaping through the intake system... what air intake system has oil in it... your engine has intake tubes that run through the sump... they have yet to be shown to leak oil... all things are possible. Got a JPI? Post some data on Savvy, copy link here. Oil only has a few routes to go to get out... 1) The case vent is pretty obvious, the oil will be all over the belly and dripping off the tail hook... 2) Getting past the rings is possible... or down a valve stem... oil will be dripping out the exhaust... the lower spark plugs will be drowning in the oil... the mosquitos won’t fly in formation with you because of the smoke show... 3) All other methods include leaking externally... having a big oil leak can be disappointing... finding the source is the beginning of getting it fixed... Help yourself, stay on target, fill in some data around your avatar... do some work for yourself... it pays off. PP thoughts only, not a mechanic... Best regards, -a- 1 Quote Link to comment Share on other sites More sharing options...
Yetti Posted September 9, 2019 Report Share Posted September 9, 2019 Start with a compression check Quote Link to comment Share on other sites More sharing options...
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