SA Flyer — Edition 263 — September 2017

82 SA Flyer Magazine

will not happen at low temperatures. A good
rule of thumb is to have an oil temperature
higher than 180°F in cruise.
During normal operation, the engine
continuously adds more contaminants to
the oil. Not only does the blow-by past the
piston rings contribute to the oxidation, but
it also contaminates the oil with various
acids and corrosive salts generated during
combustion. Some of these contaminants
cannot be removed by the filter and in time
the oil becomes saturated with corrosive
agents.
Water vapour forms each time the
engine is started or shut down. Fuel dilution
occurs during starting and, when all the
pollutants get mixed up in your lubricating
oil, it forms sludge, varnish and highly
corrosive acids.

Acids are particularly harmful when
they get wet or contain water. Your precious
engine, even in a low humidity Highveld
hangar, standing for two weeks or more,
is subject to these damaging agents
wreaking havoc with the inner parts of your
investment.
The only way these poisons can be
dumped is by regular use – getting the
oil to operating temperature (180°F and
above) and drying the oil out, so to speak.
Obviously, the more humidity the greater
the problem. It is also for this reason that
manufacturers call for calendar based oil
change periods.
It is important to note that corrosion
on the interior parts of your engine starts

within days of shut down. I strongly

recommend that aircraft be flown at

least every two weeks to get the oil up

to operating temperature to burn off

contaminants. Simply ground running the

engine will in most cases not get the oil

temperature to 180°F and ground running

aircraft engines is also detrimental.

Should an aircraft engine be out

of service for longer than a month,

the manufacturers’ engine inhibiting

instructions should be followed.

Although we would like to think our

aircraft engine air filter installations are

of the same standard as a Toyota Land

Cruiser Donaldson filter with snorkel

installation, this is definitely not the case –

in fact, it is a far cry from it. While starting

up, taxiing and even during flying, not to

mention the typical dusty conditions we

find in some parts of our country, dirty

air passes through most of these flimsy

installations, causing havoc to your engine.

Regular air filter maintenance cannot be

over-emphasized. I clean my Bonnie and

182’s filter every time after I’ve used a

gravel airstrip.

WHEN DO WE CHANGE?

The aircraft manufacturers give the

oil change frequency instructions and this

should at least be followed. My experience

is that if you have a spin-on filter installed

and fly less than 50 hours per year, change

the oil every 25 hours or 4-6 months,

whichever occurs first. If you fly 100 hours

or more per year, a 50-hour oil change

is recommended. Without a spin-on oil

filter, change the oil every 25 hours or 4-6

months, whichever occurs first. I change

my aircraft oil every 25 hours or 4 months,

irrespective of installations. Proper air filter

and induction maintenance should also be

carried out at this time.

WHAT TYPE OF OIL?

There are basically two types of oil: A

mineral base straight oil and the ashless

dispersant oil. Oil type, viscosity and of

course different brands, is a discussion on

its own.

Mineral base straight oils are mostly

used on all aircraft engines during the

running in period, although Lycoming does

not recommend the use of straight mineral

oil on the turbo charged Lycoming engines.

Ashless dispersant oils will generally be

used after engine run in because it has

additives that collect dust, assists with

corrosion prevention etc. Ashless type

oils are available in different viscosities.

Refer to the engine manufacturer for the

recommendations.

Different brands of oil, for example BP

and Aeroshell may be mixed when topping

up if your regular oil is not available, only if

they are of the same viscosity. For example,

A Shell W100 SAE50 ashless may be mixed

with another brand of ashless SAE50.

Although some manufacturers recommend

that you can mix a multi-grade with a mono-

grade, I do not recommend that. Maybe I

am from the old school, but if your engine

has been running on a type and specific

brand of oil, stick to just that until TBO.

SUMMARY

Operating in dusty areas, cold climates,

infrequent flights and long idle periods will

require more frequent oil changes than

recommended. It is imperative – and still

one of the cheaper maintenance actions

that can be carried out on your engine that

will save you thousands in the long run. Fly

your aircraft frequently and keep the filters

and oil fresh.j

BELOW LEFT - Dirty air passes through

most flimsy air filters, causing havoc to your

engine.

KNOW YOUR PLANE