CREDIT TO “Steve” on MM:
In picking up on this conversation about high oil consumption: I have a Super III with the IO-360, and my consumption is very high; I also have visible oil on the engine, and on the ground after flying.
Last year my consumption was approximately 1 qt for every 6-8 hrs, which many said is normal. This year it is 1 qt every 4 hrs. After the last oil change, I had them put oil with florescent dye in it, and I am leaking around the case bolt for #1 and #3 cylinders (think that is right).
I’ve been told that the bolts go through the crankcase from one side to the other, and you have to split the case and reseal. Others have told me to just RTV seal it to slow the leak. I have heard the price of repair could run as high as 5K. My questions are:
1. Options to try before going this costly route.
2. Should I try to seal it first and see if it works/holds
3. If I live with it could it result in any damage to the engine.
I run between 5-6 quarts. It’s messy but manageable. Any input would be appreciated.
Technical Editor:
Please read the other FAQ items related to oil consumption; just do a search on “oil consumption”.
Your oil consumption is not considered high for this engine, at power settings of 65% or higher. Two key information items that you did not mention are your typical cruise power settings, and the total time since new (TTSN) or major overhaul (TSMOH) on your engine.
Here is my opinion:
1. Have your A&P make certain that you have not lost the torque preload on your through-bolts. I don’t think that you have, or you would most likely have leaks along the case parting line. If there is just one bolt or stud that has a breakaway torque below specs, it is probably safe to re-torque it. If there are several that are found to be below spec, or if there are parting line leaks, Lycoming’s position is that they cannot be safely re-torqued. This is due to concerns about internal case fretting (that may have reduced the bearing clearance), and the resulting risk of pinching a bearing if the bolts are re-torqued.
2. Removing the bolt nut, packing sealant in the gap, then re-torqueing the nut, has been claimed by some to work. I’ve never seen it work, and few engine shops are willing to try it. For one thing, it doesn’t do anything to seal the mating line between the cylinder flange and case, where the bolt comes through. The through-bolts are a drive fit in the case, and they are sealed with a center seal (if so equipped). Some engines relied only on the drive fit for the seal, unless they were modified by a rebuilder.
3. It is incredible how much of a mess a tiny amount of oil can make. It is also incredible how much hot oil can get through a machined flange that uses no sealant or gaskets. Once you have verified the bolt torque, if you still have a leak (and you most likely will), it is a near certainty that it is not the cause of your oil consumption. Please read the other postings on IO360 oil consumption. Most oil that is used is getting burned, with no adverse symptoms (due to the nature of aircraft oil).
This will probably boil down to either postflight cleanings, repair, or overhaul. Part of it may depend on safety factors, if the leakage poses any risk of ignition from the exhaust system. That’s pretty rare, due to the high flash point of oil, with the possible exception of turbocharged engines. Unless there are other adverse wear indicators, your oil consumption alone does not suggest that an overhaul is required. However, depending on your engine time, it may make sense to do a complete overhaul if you choose to split the case for leak repair. Once you have gone that far in labor costs, it would be a shame to not get the benefit (including to aircraft value) of a zero time since major overhaul engine.