I have been working in the General Aviation fuels and lubricant area for about 45 years, and for the last four decades one of the most frequent questions I get is “what are the biggest problems in these areas?”
The answer for both is the same: Moisture in aircraft that are not flown frequently.
Where does the moisture come from?
It comes from condensation and from the exhaust, where water is a by-product of combustion.
In the lubricants area, the main problem is cam and lifter failure, mainly in Lycoming engines.
The reason that it is much worse in Lycoming engines is the location of the camshaft in the engine. With the cam above the crankshaft, it is located in the coldest point of the engine.
If there is moisture in the oil, some will vaporize during the day and in the evening it will rise to the coldest point, which is the cam and lifters.
The vapor will cause rusting. And if the engine sits for months or even weeks, there will be enough rust rouge that it acts like a lapping compound which, in turn, starts the wearing process.
Once the surfaces become uneven, the high load on the cam and lifter interface, the hydrodynamic lubrication breaks down, the wear snowballs, and then you have component failure.
What are the best ways to prevent this from happening?
The best way to get rid of the moisture is to boil it off during flight.
So what oil temperature should you shoot for?
Water boils at 212°F, but you don’t need to run the oil temperature that hot. As oil goes through the engine, it usually sees a point in the engine where the oil is around 50° higher than the bulk oil going in. This means that 212° may be too high.
I have found that 180° at cruise is the best temperature to run the engine and burn off any moisture.
When I ask pilots what their oil temperature is, most will say it is in the green band.
Two problems here: First is that the green band usually runs from 100°F to over 200°F.
The second problem is that many of the gauges have been in use for many years and may not be reliable.
What I recommend is that you remove the oil temperature sending unit. Get a hot plate, a container of oil, and a referenced thermometer. Heat the oil to 180° with the sending unit in it. When the referenced thermometer reaches 180°, paint a mark on your gauge face.
Now you need to take steps to ensure that your engine runs at or near that mark.
Remember the 50° temperature rise, so you do not need to run at exactly 180°, but try to get it above 160° even on a cold day.
Are there any other steps that can be taken to ensure full TBO life for a Lycoming cam and lifters?
Yes, proper oil changes can make a difference.
Two concerns here: Most pilots think that oil needs to be changed every 50 hours with a filter and to change oil at the start of warm weather when they go flying again.
The first problem is that both Lycoming and Continental recommend changing oil every 50 hours OR four months, whichever comes first.
The second problem is that you need to change the oil before you put your airplane away for the winter. That way you will get rid of the contaminates and acid build up in the oil and will have less corrosion during the extend period of inactivity.
In northern climates, most pilots fly mostly during the summer months and their planes see very little service during the winter months.
I recommend you change the oil late in the fall like November or December, usually with a multigrade oil.
As an added step, I would substitute one or two quarts of that oil change with an oil that meets the Mil C 6529C specification. That will be compatible with any brand or viscosity oil that is qualified for your engine. With this mixture you will have added protection, but will be able to fly anytime you want.
In addition to these steps, there are a couple of do nots.
Do Nots
First, do not go out to the airport during this time of inactivity and just start your engine with no intention of flying.
When you do that, you hit the primer and some of the raw fuel gets into the crankcase where it combines with the moisture that you did not boil off to form acids. This, in turn, increases rusting activity.
The second “do not” concerns electrical oil pan heaters. The Tanis engine heater system includes an oil pan heater, individual cylinder heaters, plus cowl plugs and a cowl blanket. This heats the whole engine assembly and some people leave it plugged in all the time and that seems to work well.
However, there are systems on the market that utilize only a large heater on the oil pan.
The problem here is that, if left on, the surface of the oil pan can be over 300°F. This high heat will coke the oil, plus vaporize any water left in the oil, which will condense on that cold camshaft and lifters. This will increase the rust activity and probably shorten component life.
The other problem is long term storage of an aircraft engine.
This happens often when a plane is being rebuilt and will be down for months or even years.
During World War II, the military shipped a lot of engines around the world and they would add straight Mil C6529C oil, hang a small metal basket containing vapor phase inhibitor (VPI) crystals in the filler neck, and then seal up all of the open ports.
A modern method people have used is to seal up the ports, back off the rockers so that all valves are closed, and then fill the crankcase completely full of oil.
Another method for Lycoming engines is to do the same steps, but only put a normal change of oil and then store the engine inverted so that the cam and lifters are completely submerged in oil.
These methods work well but do require additional clean up before putting the engine back in service.
