Why you should change your oil in Spring

[old man emu]

Here is a little extract from my Harley's Operator's Manual dealing with the effects of Winter inactivity on engine oil quality and protective ability. Note the comment relating to the build up of acidic elements in sludgy oil.

 

I reckon the moral of the story is that if you haven't been doing a lot of flying over Winter, you should change your engine oil before you launch into Spring flying.

 

 

Old Man Emu

 

 

[Yenn]

Very true, except that in central Qld our winter is often the driest time of the year. ( not for the last 3 years) Lycoming recommend every 3 months as a mminimum, regardless of hours accrued. The problem with aero engines is mainly spalling of the cams, which are wiped by the followers, stripping them of most of their oily film in the first revolution at startup. Oil is cheap compared with an overhaul.

 

 

[old man emu]

Yenn,

 

It doesn't matter if your engine is in the middle of a desert, or a jungle, one litre of fuel will produce the same amount of water. Some of this combustion byproduct will find its way into the crankcase. If the crankcase ventilation works, the water vapour escapes into the atmosphere. When the engine is shut down, there will be vapour in the crankcase that hasn't vented. It will condense and sit on top of the oil. During the next start up sequence, this water can be stirred into the oil by the moving engine parts. If this happens enough, the water will remain in suspension in the oil.

 

Water does not maintain a neutral pH. It can dissociate into acidic hydrogen ions and alkaline hydroxyl ions, thereby making the oil/water mixture chemically active on metals. That's what causes the corrosion of the surfaces of crankcase components.

 

OME

 

 

[fly_tornado]

Doesn't the moisture come from the atmosphere?

 

 

[facthunter]

Many times on this forum I have pointed out that for every gallon of petrol burnt there is over one gallon of water produced. This is the most significant source of water contamination of oil in the sump as some blowby always happens past the rings. If the engine is not hot all over condensation will occur inside the engine and water will be absorbed and suspended in the oil. These fine water particles will combine with combustion by-products and form acids, alkali's salts etc which are highly corrosive of many engine internals, ((as OME has said) this is why it is necessary to change oil regularly and try to run the oil temp at around 85 degrees C, and avoid short engine runs followed by non use.

 

Engines not used for longish periods should be inhibited with special substances. It's quite a procedure but it's documented on plenty of sites.CASA would be one reference. Nev

 

 

[old man emu]

Doesn't the moisture come from the atmosphere?

No. The water is the product of the combustion of the hydrocarbons which make up petrol. I've forgotten the general ratios of the atoms in a typical fuel hydrocarbon (carbon:hydrogen: oxygen) but in general, burning a hydrocarbon fuel produces carbon dioxide and water. You should also remember that there are molecular impurities in fuel which introduce nitrogen and sulphur to the mix, and as a result of their combustion, nitric and sulphuric acids form part of the exhaust gas mixture.

 

OME

 

 

[Yenn]

There would also be damp air drawn into the motor as it cools after flight. A fair amount of water can get into fuel when the tank cools overnight, but I imagine the amount being sucked into a cooling motor would be more.

 

 

[facthunter]

The sump capacity would be lucky to be 8 litres total volume. There would be some air though, but I don't feel it is the major factor.

 

The formula for fuel is about C6 H 13 I think paraffinic series are Cn H2n+1. (Vev would know) and the combustion products are H2O and CO2

 

If you find the atomic weights you simply apply them and you will get a ratio. Nev

 

 

[spacesailor]

Any one seeking an "eletric sump-plug" sold in the UK in the early 50 tis, 240 or 12 volt, also "electric windshield defroster's"

 

spacesailor