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Mooniacs, Flying my M20F with an IO360a1a, turbo normalized (ray jay)...went for a little scenic cruise yesterday and here's what happened: 1) Oil was just above 6qts, so I figured I'd add another qt before the next flight 2) Leaned for taxi, rolled to the threshold, and did my run up. First click on the mags and the engine loses 200 rpm, runs rough. Ok on the other mag. Ok on both. So I rev up to 2200 rpm, lean for best power, hang for 30 seconds and check the mag again. Still rough. I repeat the leaning/fouling rectification procedure and this time it works, everything is fine and dandy. However, I notice cyl #2 has crept up to 405. I pull the power back, but since its hot as hell 90degrees, high DA 8500ft, and not a lot of cooling, I don't see much of a drop. I think to myself, let's roll and see what happens. 3) So I line up and go WOT and #2 goes up to 420. I abort. Head the FBO. Drink an iced tea. Add a qt of oil. Wait 20 mins. 4) I try again. No fouled mag check. Temps all stay low (350-370). I go WOT no turbo (24inches, 2600 rpm, but the rpm takes 5 seconds to spool, kinda hangs at 2400 for a bit then get to 2600 on the roll), I hit 410 on climb out on #2 but that comes down quickly after I nose over and speed up to 115 for cruise climb (full rich, no turbo, 24/25). At 8000 feet, I add the turbo just to see how it affects the temps, all good. I lean. All good. So, what happened? EGTs were all fine around 1290-1360. Could I have stressed the cylinder that much during the plug foul operation to make that one cylinder that hot? If #2 had the fouled plug, I would expect the CHT to be lower...#1 340, #2 420, #3 380, #4 340... I don't have the GEM computer to download any data so you'll just have to go with the above. Mind you, my #2 is always the hottest by about 20 degrees compared with #3 and by 30-40 degrees compared to #1 and #4. Interesting that 1 and 2 are both in front, and that 1 has more baffle around it and it looks like #2 is intentionally missing a few inches baffling (#1's go straight across the entire length of the cylinder and #2 has a 3 inch gap between baffle pieces). Also, #2 is about 70 hours new, I so I get that the higher temps could be a break in thing. About 20 hours ago I replaced the mineral oil with 100Wplus. Thanks for your thoughts! B