Morne
Line Up and Wait
- Joined
- Sep 18, 2011
- Messages
- 699
- Display Name
Display name:
Morne
So I was out flying today and my EGT started climbing about 1h 30m into my flight.
I was over central PA when this happened and my first thought was, "Well it must be carb ice." OAT at 7,000' was right around freezing, much warmer than at the surface. I have experienced carb ice before, even at cruise, so I applied carb heat. That worked, to some degree, but I was really chasing the EGT with the carb heat knob. It was a LOT squirrelier than other carb ice events. I tried enriching the mixture, no change. I tried re-leaning the mixture and it ran rougher than I liked, so went back to richer. The CHT didn't flinch the whole time. All analog, single point gauges (yeah, yeah, I know - get a nice digital engine analyzer with sensors on every cylinder).
I called ATC and adjusted my route to go over a class D airport on my route in case I decided to land and sort things out. I started messing with everything I could think of wondering why it was behaving so oddly. Then I tried switching from my right tank back to both (I had switched from both to right only at 0h 30m into the flight). Almost immediately the problem abated!
What does that say to you?
My working theory is that there was a little bit of water contamination in the right tank that was frozen while on the ground during my preflight check. After an hour plus at cruise it warmed up and started going through the engine, behaving kind of like carb ice (leaning the mixture more than my mixture knob setting indicated it should've). Carb heat helped it some, but the real fix was to dilute it by pulling from both the left (presumably non-water containing) tank and right tank at the same time. Sound plausible?
I was over central PA when this happened and my first thought was, "Well it must be carb ice." OAT at 7,000' was right around freezing, much warmer than at the surface. I have experienced carb ice before, even at cruise, so I applied carb heat. That worked, to some degree, but I was really chasing the EGT with the carb heat knob. It was a LOT squirrelier than other carb ice events. I tried enriching the mixture, no change. I tried re-leaning the mixture and it ran rougher than I liked, so went back to richer. The CHT didn't flinch the whole time. All analog, single point gauges (yeah, yeah, I know - get a nice digital engine analyzer with sensors on every cylinder).
I called ATC and adjusted my route to go over a class D airport on my route in case I decided to land and sort things out. I started messing with everything I could think of wondering why it was behaving so oddly. Then I tried switching from my right tank back to both (I had switched from both to right only at 0h 30m into the flight). Almost immediately the problem abated!
What does that say to you?
My working theory is that there was a little bit of water contamination in the right tank that was frozen while on the ground during my preflight check. After an hour plus at cruise it warmed up and started going through the engine, behaving kind of like carb ice (leaning the mixture more than my mixture knob setting indicated it should've). Carb heat helped it some, but the real fix was to dilute it by pulling from both the left (presumably non-water containing) tank and right tank at the same time. Sound plausible?
