why is it so ??

[Russ]

my jab engine, for that matter all aero engines........use oil, its apparently normal.

 

If our motor vehicles consumed oil at the same rate, we'd be concerned. ( my toyota from 1 service to the next, uses next to nothing )

 

So.........why are we using oil in our well maintained 4 stroke engines. ( puzzles me )

 

 

[Nobody]

Air cooled engines operate over a wider temperature range. This means that there needs to be more clearance between the piston and the cylinder hence higher oil consumption.

 

 

[bexrbetter]

Four minor reasons;

 

1/ Air cooled engines do need slightly more piston to bore clearance.

 

2/ Air cooled engine's bores do tend to have ovality.

 

3/ Air cooled engines run hotter evaporating more oil.

 

4/ Flat engines don't naturally drain oil away with gravity.

 

One major reason;

 

1/ No PCV system.

 

Oil rings work, not by the myth of "scraping" as many people believe, but by a pressure differential between the upper cylinder and the crankcase. PCV stands for 'positive crankcase ventilation', almost a misnomer as it creates a negative pressure crankcase environment increasing the fore mentioned pressure differential.

 

Layman's terms; A PCV system sucks the oil off the bore walls betterer.

 

And yes, if you want semantics, oil rings, and the very misunderstood 2nd ring, do "scrape" oil, but only into position so the oil can be evacuated through the holes or slots in the oil ring groove due to the pressure differential.

 

 

[Yenn]

If you ran your car engine at the same power as you run an aero engine I doubt that it would be as low an oil user as you think. Have you ever been able to run your car flat out for 5 minutes?

 

 

[bexrbetter]

Have you ever been able to run your car flat out for 5 minutes?

Absolutely, without a moments hesitation and many recent examples.

 

One of the biggest myths that floats around the aircraft scene is that a car engine can't run at the same levels as an aircraft engine - it's total nonsense.

 

... and that's when the fight started ..

 

 

[Doug Evans]

:roflmao:aircraft engines stated life in a old ford model T I be-leave ! or VW:scratching head:

 

 

[Keith Page]

Absolutely, without a moments hesitation and many recent examples.One of the biggest myths that floats around the aircraft scene is that a car engine can't run at the same levels as an aircraft engine - it's total nonsense.

 

... and that's when the fight started ..

I think the car engines run a lot harder.

Go back to the days of being a country boy on the country roads, those engines stayed together, none went bang but a few boiled their way along.

 

The other thing the poor old engine used to get over the 3k rev range and be kept up in the high ranges for more than a couple of minutes.

 

Regards

 

KP.

 

 

[Nobody]

A rotax 912 doesn't use very much oil.....

 

 

[Russ]

If you ran your car engine at the same power as you run an aero engine I doubt that it would be as low an oil user as you think. Have you ever been able to run your car flat out for 5 minutes?

Have been running subaru car engines in my gyros for umpteen yrs, latest was a soob ej25, they run 4000+ all day every day, use zero oil.

 

 

[turboplanner]

my jab engine, for that matter all aero engines........use oil, its apparently normal.If our motor vehicles consumed oil at the same rate, we'd be concerned. ( my toyota from 1 service to the next, uses next to nothing )

So.........why are we using oil in our well maintained 4 stroke engines. ( puzzles me )

There is a good thread on this from maybe a few years back, have a search.

 

In any engine, before deciding it is burning oil:

 

1. Always accurately measure and write notes of amount of oil added, and time/hour interval (You'd be amazed at the stack up error when people round out.

 

2. Record always measure oil with the dipstick plunged to a set level

 

3. Always measure with the aircraft level on a known pad in a known direction and with the engine in the same state - preferably cold after an overnight drain, or hot immediatey after use, but not while oil is draining down.

 

4. Always ensure that the engine is not being overfilled, because it will get rid of this oil and SEEM to be burning it. All engines have a different max, or method of determining when enough is enough (and this is the best part of the thread I remember because the guys, who KNEW, spelled out what that was.

 

These four things solve most problem engines when they are put on oil report.

 

I understand you might already have covered most of this given your comparison with the Toyota, but that overfill position on the Jab could just be the answer.

 

 

[Russ]

No turbs, I'm not concerned about excess oil in my jab, ( 15.....20ml hr ) have accurately monitored now.

 

I was puzzled...why do we use oil, compared to autos.

 

 

[Tomo]

A rotax 912 doesn't use very much oil.....

'cause it 'tis water cooled.

 

 

[Nobody]

'cause it 'tis water cooled.

Exactly....

 

 

[facthunter]

A jab will vent more oil than it burns. Older aircooled engines always used a lot of oil, (especially radials). Nev

 

 

[fly_tornado]

BMW R twins have oil cooled pistons and exhaust valves and also do not consume oil

 

 

[Teckair]

my jab engine, for that matter all aero engines........use oil, its apparently normal.If our motor vehicles consumed oil at the same rate, we'd be concerned. ( my toyota from 1 service to the next, uses next to nothing )

So.........why are we using oil in our well maintained 4 stroke engines. ( puzzles me )

I know of a Jabiru in a flying school that could not complete a cross country flight without having to land and top up the oil. The 912 Lightwing I fly goes from one oil change to the next with out a top up. My VW powered planes also used very little oil.

 

 

[Nobody]

I know of a Jabiru in a flying school that could not complete a cross country flight without having to land and top up the oil. The 912 Lightwing I fly goes from one oil change to the next with out a top up. My VW powered planes also used very little oil.

Thats a bit extreme. But I also know of one school in the USA with a policy of filling their lycoming to a level that meant that it lost most of it out the breather....

 

 

[Yenn]

When I said car engines I meant engines in a car and you have a problem working them full bore for 5 mins. The straight roads are not long enough.

 

I run a Jab 2200 and a Lycoming 0-320. Both use hardly any oil. The Lycoming nil in the last 20 hours and the Jab might take 150ml between changes. Both of them are never filled to the top mark on the dipstick. That would result in a load being blown out the back.

 

 

[SDQDI]

If your roads aren't straight or long enough you must be in the wrong place Yenn

 

When we were out west our poor old turbo diesel used to sit on 3500rpm for hours on end, redline was 4000. Still didn't use oil unless you went over ten thousand before you changed the oil. I'd say Bex has the nicest answer for this one:thumb up:

 

 

[Ultralights]

my 912 goes the 50 hrs between services before needing a top up, my air cooled BMW motorcycle goes 5000,km before needing an oil top up...

 

 

[facthunter]

Some oils evaporate a % when first used. Engines shouldn't leak oil if they are built right. In our current environmental concerns, low oil consumption is forced on us for road use. It can cause carbon deposit build up in a motor but often some dust is involved in this with aircraft. Also the engines often run richer than normal, causing deposits and darkening of the oil.

 

I wouldn't get fixated about oil use. You are supposed to have a film of oil on all moving parts. Rings seal better with some oil around. Aircooled engines run hotter so are more critical. Oil helps stop corrosion.

 

It's not possible to use none. Some engines actually suffer from oil dilution to a greater or lesser degree. This can offset or counteract the apparent lack of oil use. Some components of fuel have very high temp boiling points and remain in the oil once there, diluting it and reducing it's value as a lubricant. Nev

 

 

[Yenn]

There is a difference between running an engine at max rpm and full power. Running flat out, or full power may not even reach max revs, but it is alot harder than max revs. You only have to look at the CHTs to see what the difference is.