Bad Gas. I'm Never Going to Costco Again!!

A few weeks ago when I was up for a local flight, the engine began to run slightly rough.  At first, I thought it was my imagination, but as I flew along, it actually stumbled for a nano second and my adrenaline spiked.  Steve Coonts in his book The Cannibal Queen calls it a "lummer--a shot of cold urine to the heart".  Urine, adrenaline--same concept I guess.

Anyway, it certainly got my attention.  I peeled off back toward the airport and on the way checked the mixture and mags.  The mags were fine, but as I leaned the mixture, the power climbed quite a bit more than usual before it fell off.  Normally during leaning at cruise, the power moves slightly higher, then drops off as the mixture moves lean of peak.  In this case, it climbed.  A lot.  Hmmmm.  Symptomatic of an overly rich mixture??

When I got back on the ground, everything seemed fine during taxi.  But I felt that the engine was running a bit rough at idle.  Or was it my imagination again?

Back in the hangar, I decided to have a look at the plugs.  Their colour is generally a good indication of the state of the mixture.  White or light grey means too lean, light brown is good, dark brown or black is too rich.

I unscrewed the #1 cylinder lower plug  and had a look.  It was soot black!  Not just black in colour, but coated in black soot!  What the ^&%&????  That could be big trouble!!  A stuck valve?  Blocked air intake?  Who knows, but clearly that cylinder was in trouble!

I unscrewed the #2 plug.  Same thing!!  #3 and #4 were also the same!  Soot black.

Ok.  So it wasn't a single cylinder problem.  It had to be carburation.  I checked the air filter.  Clean. No obvious blockages in the intake system.  Hmmm.  Time to talk to Chris my AME.

Chris said yes, it could be a carburetor problem and it might need to be overhauled.  But with only 600 hours on the engine that seemed unlikely.  But he was super busy and couldn't get to the plane for several weeks.  Great.

And then he asked:  "You run car gas right?"  I said yes, most of the time.  He asked: "Where do you get it".  I told him Costco.  I use their premium which doesn't have any ethanol.

He said:  "I remember a fellow a while back who got a load of bad car gas from somewhere and it made his engine run really roughly.  He switched back to avgas and it smoothed out immediately."

OH REALLY??!!!

That was enough for me to hear!  I headed back over to the plane and immediately drained out the gas into several jerry cans.  I then taxied (still seemingly running roughly) over to the airport gas pumps and filled the tanks with 100LL.  At $2.18 per litre it cost over $300!!  Still if that fixes it, it would be worth every penny!

I fired up the plane.  It  ran roughly for a minute or so and then noticeably smoothed out!!  Whoo Hoo!  That was the freaking problem!!

I took the plane flying and it ran normally.  After landing I pulled the plugs.  They were now perfect!  A nice light brown.  No soot at all.  Thank you Lord!!!

Needless to say, that was the last time I bought gas at Costco!   Clearly, the price of their premium gas was attractive, often 20 to 30 cents less than the name brand guys.  But definitely a bad idea.

After checking around on the internet, I determined that Shell Premium had a reputation of being the best quality gas available.

Needless to say, that's where I'll be going from now on!!