Bad English, I know.
So, I designed an engine in 1989. Once revised it in 2008, but the new revision has MTBF about 30000 km. But if I design a new engine with same parameters in 2008, it has much better charateristics, including MTBF above 65000 km. Well, the question: is it bug, or feature?
Upload both engine files here and we’ll take a look. 
Here they are. FX17T is a “bad” engine, RK17T Is “good”.
2008 RK17TRev1.lua (73.3 KB)
2008 FX17TRev4.lua (73.3 KB)
For me, both engines show up as having almost the same MTBF at around 65000-66000 km. The problem you are experiencing may be the saving bug that still is in the version.
Ok, thanks. After closing and launching the game again problem solved by itself.
Call me dumb but what does MTBF stand for and mean?
Don’t worry, it has been asked a lot.
The Mean Time Between Failures is the average running time of the engine before the slightest failure (still runnin’ but not as good).
So it’s somewhat the time you’ll have left when you fixed it before the next fail.