Here is a copy of article.
Herewith an incident I had with diesel in petrol. I'm sharing this to create awareness, so here goes:
On Saturday I decided, on short notice, to fly to a meeting Outjo to Otjiwarongo (1/2hr), and from there to Tsumeb (2hrs). From the word go I was late for the meeting and had less than an hour to get my Hawk ready. I needed petrol and found my normal fuel container 3/4 full. Which was weird, because I always empty them (What doesn't fit in before a flight gets added after), but what was inside looked and smelled like unleaded, so I just added petrol at the pumps to fill them completely and off I went.
During warming up I noticed a little bit of blue smoke coming from the exhaust when looking at it against the sun. By the time I got the hangar doors closed I had already forgotten all about it. En route to Otjiwarongo I found that I burned 11.8l/h instead of the normal 11.0 @ 4,900rpm, but put it down to weird and ignored it further. The EGT's looked slightly lower than normal, but the weather was cooler so that explanation was tagged to the problem. In Otjiwarongo all was normal. I even took a friend for a short scenic flight before I departed to Tsumeb. During the pre-flight in Otjiwarongo I didn't check the oil level. How much oil can one lose in 40 minutes, right? En route I noticed that the 912 UL seemed to run slightly erratic, the revs dipped from 5,000 to 4,800 every now and then. When I applied full throttle the engine responded fast and willingly and settled back on 5,000 easily. This puzzled me, but it was turbulent and I was busy dodging rain showers, so I found another convenient explanation: Obviously the turbulence I ran into caused the motor to labour every now and then. Problem analysed and explained away.
On landing in Tsumeb I found my oil container brim-full and every drop of oil that couldn't fit into the tank (which was a lot) spread evenly over the tail feathers. After a whole day of trying to find an explanation (it isn't easy at all to explain 1.5l of oil gained during the flight) I latched onto a possible solution and traced the fuel supply. The "petrol" came from a diesel car that was wrongly filled with petrol at the pumps. The mixture was drained and stored for further use. I had actually witnessed the whole operation and was also concerned that "my aircraft fuel containers" were used for the job, but I'd mos know about it and not forget. Right.
The 912 is fine. Except for a red face, so is the pilot. The spark plugs were cleaner than I have ever seen them, it looked like a layer of coke had been loosened from the pistons. We drained and refilled both oil and fuel and changed all filters. The magnetic oil plug was clean except for a single sliver of metal. I'll have the oil analysed to check, but the Hawk behaved very well during the flight back to Outjo, which was conducted at ample altitude for a possible emergency landing.
I fly a low compression 4-stroke. With a higher compression engine like the 912 ULS the story may have ended differently, or finally. Thus to repeat my instructor's lessons:
• Don't be rushed when tending to your aircraft.
• Make sure about your fuel supply. Repeat, make *sure* about your fuel supply.
• Don't take deviances from normal lightly. My fuel consumption wasn't normal, neither were the lower EGT's and definitely not the fluctuating revs.