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Engine Oil

Water cooling means tighter tolerances so the oil gets much less crap into it.

You mean tighter clearances, not tolerances.

There are plenty of air cooled engines that use piston/cylinder clearances as tight as a water cooled engine, motorcycle engines since the early ‘80s are typical in that regard and run clearances of about 1.2 thousands of an inch (0.03 mm). The difference between them and typical aircraft engines is the use of cylinder and piston materials with similar coefficients of thermal expansion.

I change my aircraft oil about every 25 hrs because it’s easy, and makes the exact timing of when I do it unimportant.

Last Edited by Silvaire at 23 Mar 17:24
I´d say most aero oils are detergent types as well, just less so than special Diesel types . And breathing into open air cannot be much relevant to oil changes as air goes OUT. Tighter tolerances , well, there are limits when you got huge cylinder bores. There are always aluminium pistons working in mostly cast iron blocks so there is heat growth to see, same with aero engines. But there are lots of factors why truck engines go tens of thousands of hours with no troubles – unlike typical aero engines. Vic
vic
EDME

Car/truck engines are very different. Water cooling means tighter tolerances so the oil gets much less crap into it. Also they use detergent oils which keep the engine much cleaner; these oils can be used (with much caution – previous threads) in our aero engines, briefly. The crankcases are vented only via the inlet manifold, not wide open to the outside, etc, etc.

Administrator
Shoreham EGKA, United Kingdom

vic wrote:

What do you think about oil change intervals on truck engines ? They´d have to do them each week when 50 hours were so important. Plus these engines work really hard most of the time – quite unlike aero engines which do some high power climbs but then just see half power settings for the rest of flight. Vic

When I was young I installed a bypass oil filter in my car, claiming that you never would have to change oil again. They say that the oil changes its consistency and could last forever.

It was a Volkswagen Golf 2 Diesel, and I had it over 100.000 kilometers without changing the oil. Sold it in good working condition.

However, regarding aircraft engines I have angst and change at least every 50 hours

By the way the manufacturer of these filters still exists, Trabold (German only)

So what’s the truth about oil? There are voices for any opinion.

Germany
What do you think about oil change intervals on truck engines ? They´d have to do them each week when 50 hours were so important. Plus these engines work really hard most of the time – quite unlike aero engines which do some high power climbs but then just see half power settings for the rest of flight. Vic
vic
EDME

I have lots of oil analysis data – various threads – but nothing going anywhere near 100hrs.

I would expect the oil to be practically useless.

I’ve never gone past about 60. The oil consumption certainly goes up – see above link.

There is this which suggests some owners may be doing 100hr servicing, but I have never found an SR22 owner willing or able to confirm this.

Administrator
Shoreham EGKA, United Kingdom

Bathman wrote:

I could go with 100 hour between oil changes on unleaeded fuel but I’m no so sure about when using leaded fuel. Has anyone ever ran and oil analysis when operated to 100 hours?

Oil is so cheap relative to the rest of flying I don’t see a good reason to not change it frequently. I doubt I have ever hit my hour limit between changes, since I don’t fly that often. It’s usually the time limit. My analyses from Blackstone show good numbers – I run Phillips x/c 15w50 with Camguard and have an engine dryer.

If you don’t change the oil filter, it takes about 20 minutes start to finish to change the oil through the dipstick with an oil extractor. If you fly a lot and don’t need camguard, the cost of the oil is less than 100 euros, or 2 euro per hour if you change at 50 hours.

Fly more.
LSGY, Switzerland

I do 25 hour oil changes, avoid starting engine unless I’m going to fly at least 1 tach hour, try to fly at least every 2 weeks, and change the oil filter at 50 hours. Presently just over 1/2 TBO.
These longer intervals may work for aircraft flying many hours almost every day, when the engine is limited to manufacturers TBO.
Most of our non-commercial aircraft go well over recommended TBO.
(But one was successfully landed last year after the engine seized, the crankshaft snapped and the composite propellor shredded, far beyond recommended TBO.)

Maoraigh
EGPE, United Kingdom

I was chatting to an FI the other day who works at a not very local school. They have moved there entire fleet (C152 and PA28-161’s) onto 100 hours between oil changes. They do have UL91 at their home base but are actually using 100LL as its cheaper.

A year or two ago I used to fly a PA28 that was on 75 hour oil changes and I have to say the oil looked pretty ropey come 75 hours.

I could go with 100 hour between oil changes on unleaeded fuel but I’m no so sure about when using leaded fuel. Has anyone ever ran and oil analysis when operated to 100 hours?

By9468840 wrote:

I use camguard and try to regularly fly the aircraft even for 15-20 minutes to get the oil temperature high enough to get rid of vapor.

I would add crankcase moisture control between flights unless frequent.

Antonio
LESB, Spain
134 Posts
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