In the fall, farmers think of harvest, young boys think of football, and pilots’ minds turn to whether to use single grade or multi-grade oil in their airplanes for the winter.
So which one is better for your engine?
If we look at the benefits of a multigrade oil, most of the pluses are in cool or cold weather.
Multigrade oils flow better during a cold start, so the engine cranks faster, which is easier on the battery and starter. Another plus: Multigrade oil gives you a better chance of starting, especially if pre-heat is not available.
The really big benefit is that multigrade oils get to critical bearing surfaces quicker after the engine does start.
So, what could be the down side of a multigrade oil?
Multigrade oils leak more than single grades. This means that if your aircraft tends to mark its territory, a multigrade oil will increase the markings, which can be a problem on your floor and give your mechanic a headache.
Also, if your intake guides are too loose, your engine will use more oil with a multigrade oil.
The gray area in this discussion is oil consumption past the oil rings. Multigrade oils tend to reduce the oil consumption past the rings by 30% to 50%.
Most pilots think that the lower the oil consumption the better, but that is not completely true. If you remember my column “Engine Break-In 101,” one of the major points of the article on the proper way to break in your engine was that during operation, a very small amount of oil remains in the honing valleys of the cylinder walls when the pistons move down. This oil helps seal the compression rings and increases the heat transfer from the piston through the rings to the cylinder walls.
In a liquid-cooled engine, this is not very important. But in an air-cooled aircraft engine, this can be important, especially in larger turbocharged engines.
As an example, many years ago, Continental redesigned the rings in many of its engine lines. With the new rings, oil consumption over 10 hours was just a quart and customers were very happy — until they needed to replace the cylinders prematurely.
If your oil consumption past the rings is very low, then using a multigrade oil that lowers oil consumption can increase cylinder wear. The question is what is your oil consumption past the rings? Not the total oil use, but just that past the rings. If it is real low, then the use of a multigrade may lower it even further. This concern is mainly in larger turbocharged engines and mainly during hot summer days.
What oil should you use?
So what oil should a pilot use?
I recommend that if you live in the southern part of the country, use a single grade oil in the summer months and then maybe one multigrade oil change in the winter, especially if you plan to fly north in the winter or if you do not have pre-heat equipment in the winter.
If you live in a northern area, I recommend using a multigrade oil most of the time, but use a single grade oil in the hot summer months.
Changing the oil at least three times a year or every 50 hours (if you have an oil filter) is one of the two most important things you can do to protect your engine. The second? Make sure your oil temperature is around 180°F at cruise.
How do I determine if my oil cindumltion is past the rings or not?
When you say the oil temp should be 180 degrees, do you mean no hotter than that or at least that hot?
Thanks
It is not easy to determine if your oil consumption is past the rings or the guides. Generally, if your oil consumption goes up when you switch from a single grade to a multi-grade, it means that your oil consumption is past the guides or leaks. If it goes down, than your oil consumption is past the rings. But if you have consumption past both, it can go either way.
The 180F is a general target. If it is way below that, you will not boil off the water and if it is well above that, you can cause carbon deposits and other problems in the engine.
Another thread that can go on forever.
In owning 4 airplanes with Continental and Lycoming engines in the course of 23 years, I’ve used them all: (single viscosity petroleum, multi viscosity petroleum and multigrade semi synthetic). They have all served me well. Perhaps religiously changing oil every 25 hours even with a filter has helped?
As far as leaky engines, regardless of oil type, engines will leak if seals and lines are not up to snuff and of course, radials are supposed to leak regardless.
My last Lycoming 0235 C2C and my current Continental IO470N have left the ground bone dry due to seal, line and gasket replacement as needed..
I follow Mike Busch on his advise on oils. He has published a few articles, ‘All about Oil’ , and ‘ Slippery Stuff’, in the EAA magazine. They can be found on the web.
He also discusses mineral oil vs the semi-synthetic, multi-grade oils.
There’s another point to ponder IF your airplane sits a lot. Multi-grade oils are pretty “slippery” and tend to drain off of metal parts faster. I poke a hole in the oil filter to allow draining into a bread pan prior to removal. After draining that oil into my oil recycling container, I tip the pan up so I can collect the last of the residue. Overnight, multi-grade oils tend to totally drain off the side and down to the bottom. In warm climates, the pan’s bottom is darned near dry. Single grade oils tend to stick around longer. SO … for me … I like single grade oils and put up with pre-heating requirements.
Remember the engine components are hot when your engine shuts down, which thins single grade oils. Your cake pan would need to be hot and hold that heat similarly to an engine for a period of time to make your comparison valid.
That’s why Mike Busch advises to use ‘Camguard’ to protect from rust,
in has articles , starting with, ‘All About Oil’ – Savvy Aviation Resources.
BTW, the multi-grade oils that are semi-synthetic will leak more than mineral oils.
At operating temperatures the single grade and multi grade viscosity are almost the same, so both oils will drain off similarly. Both leave an oil film behind after engine shutdown; however, multi grade oil will drain off the parts faster as the engine cools when compared to a single grade because the multi grade oil is thinner at cold temperatures.