Engine Oil

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.

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.

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

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.