SEIZING PISTONS

Be aware that on 2002 and later 996/7's that display misfire codes, smoke, and have high oil consumption, the symptoms might indicate that the pistons are seizing in their bores.

I have seen a few with these symptoms; and after performing a compression and leakdown test , I found that the compression was lower on the cylinders that coded the most frequently. The leakdowns were additionally in the 20 to 30 percent range.on the suspect cylinders. I then borescoped the cylinders. Here are some photos of the damage:

Note the crack in the second and third picture.

Here is an 04 4s with 65k. Both rear O2's were starting to fluctuate . The engine coded very breifly with an 300/306 (in memory). the roughness factor was higher on #6 , #1 and #2. This is #6 cylinder.

It seems that one common symptom is a tapping sound that originates at idle during the cold start. It then increases in magnitude will occur when the engine is fully warmed. Noticeable oil smoke will be emitted through the cats.

Here (above) we can see the left side of the scoring of #4 cylinder.

















Here is a shot of the center of the scoring
















Her is another shot of the scoring. Note the bluish tinge of color

















Another shot of left side of border of seizing

Picture of right hand border of scoring

















This is a view down the bore near the top of the piston. Note the color is more blue and the scoring is much deeper. In my opinion the oil had failed here. This is truly a seizing situation. The engine had a short term tapping when cold (breifly) and emitted a puff of blue smoke (for about a quarter of a second) out of one tailpipe.
Consider where is this particulate matter (metal scrapped off of the wall) is going (through the filter and scouring everything in its path); also as a minor point the damage to the cat from clogged burnt oil. At the point the engine is history..