Bore scoring is damage on the cylinder wall and on the piston. Coating on the piston skirt wears through, piston rubs the wall and leaves vertical marks. Gap gets bigger, piston starts to rock and tap, and later engine starts to use oil.
On the flat six it is most common on the 3.6 and 3.8 in the 996 and 997 Carrera from 2002 to 2008, and on the 3.4 in the 2006 to 2008 Cayman S and 2007 to 2008 Boxster S. The 2.5, 2.7 and 3.2 get it rarely. First 996 with the 3.4, 1999 to 2001, gets it less often, but this engine has its own weak points. Top of the cylinder can crack, the so called D-chunk, and heads can crack too. Many of these engines go past 100,000 miles before it happens. Mezger engines in the 996 and 997.1 Turbo, GT2 and GT3 up to 2011 have Nikasil bores, this kind of scoring they simply don't get.
The 9A1 engines from 2009, in the 997.2, 987.2, 981 and 991.1, get it way less, and the base 2.9 and 2.7 almost never. When 9A1 fails, usually it is a different thing. Cylinder gets a little smaller at the bottom, near the main bearings, and piston seizes there. Builders who measured these engines found it on an end cylinder every time, and failures came in winter. On 2014 to 2016 991 and 981 there is one more reason. Porsche found ignition coils with bad diode, and the repair in their bulletin starts with checking the cylinder walls. Fixed coils are marked NEW, so I pull one coil and I know what the car has. The 991.2 and 992 Carrera and the four cylinder 718 have iron coated cylinders, and there is no known pattern of scoring there.
Not only sports cars. Cayenne V8 gets it too, mostly the 4.5 in the 955 S and the 2008 4.8, especially Turbo, and mostly on cylinders 5 to 8. The 2015 to 2018 Macan S, GTS and Turbo have twin turbo V6 from same family, same kind of cylinders, and I had Macan Turbo with scoring myself. The 3.0 single turbo V6 from 2019 has thin iron liners, and scored ones show up there too. On the Audi version of this engine the pistons crack at the skirt.
Cylinders in these blocks are aluminum with silicon in the surface. When silicon particles break out and skirt coating wears through, aluminum runs on aluminum. Fuel washing the oil off the wall makes it start faster. Leaking injector, misfire, vacuum leak, bad sensor, all of this does it. Heat too. On the flat six it is almost always bank 2, cylinders 4 to 6, and cylinder 6 first. On bank 2 the side where piston pushes is the top of the cylinder, farthest from the coolest coolant. Measured on running engine with stock thermostat, this side runs about 9 degrees F hotter than same side on bank 1.
Most of the time first sign is a tick, and it sounds exactly like lifter or something in the valvetrain. Same rhythm. But hydraulic lifters on these engines almost never tick, bad lifter shows up as misfire first. So on these engines, tick is bore scoring until borescope says no. Believe me, too many scored engines get new lifters first and the tick stays. Scoring tick does not go away when engine is hot. Smoke on start up gets blamed on the air oil separator, and many scored engines get new AOS before anybody looks inside the cylinders. And some engines show nothing, no noise, no smoke.
Soot on one tailpipe is a hint, not a proof, rich running engine does it too. On a 911 bank 2 is passenger side, so look at the right tailpipe. You may hear driver side, but Porsche parts catalog puts cylinders 4 to 6 on the right. On Boxster and Cayman engine sits the other way around.
Compression and leak-down can look normal on scored engine, because oil seals the rings. You have to look with the borescope. Scoring starts low in the cylinder, in the part the piston covers when it is at the bottom. Through spark plug hole you see it only when it is already advanced. So I look from below too. Sump plate comes off, piston goes to the top, and camera looks up into the cylinder. Bank 2 first, top side of the bore where piston pushes, then bottom side.
Numbers help too. Crankcase vacuum with manometer, engine hot, A/C off, at idle: about 4 to 6 inches of water on these engines, and about 15 on the 2009 to 2016 direct injection flat six. These are sea level numbers, up here at 7,000 feet it can read lower. Oil analysis can show aluminum and silicon going up, but normal analysis misses bigger particles, so I cut the oil filter open too.
Reading the camera takes experience. These cylinders have no cross-hatch like iron bore, and camera light makes small marks look worse than they are. Real scoring has depth, it cuts under the shiny surface. Good engines get condemned because somebody read the picture wrong. 13 years on these cars every day, I know what I am looking at.
Porsche's own limit for oil use on these older cars is up to 1.5 liters every 1,000 km, about 1.6 quarts every 620 miles. With this number dealer can call scored engine normal. I go by the camera. When engine uses more than a quart every 600 miles, it is time for rebuild.
There is no good bore scoring, but light marks low in the bore can be watched. Then I tell the owner how to live with it. Different oil than the factory one. No lugging on low rpm and high load. Always proper warm up, and warm up means driving gently under 3,000 rpm until oil is warm, not idling in the driveway. After hard drive and stop at idle, pull away gently for first few seconds. Oil use and filter get checked every service. Deep grooves high in the bore, this is the end of that engine.
Fix on the M96 and M97 is full teardown and new cylinder liners. I send the block out for the highest possible machining known to me. Iron sleeves are not the answer on these engines. They grow different than aluminum block with heat, they slip and they leak. On the 9A1 the block can be bored and plated directly, or cylinders get new plated liners. Factory replacement engine has same cylinders, same problem like the old one. If a 957 Cayenne gets new block from Porsche, all pistons and rings must be new too. Porsche changed cylinder finish and rings during production, and mixing old and new damages the cylinders.
What helps: lower temperature thermostat, it cuts this bank 2 difference to 2 to 4 degrees F. Third radiator on manual car can overcool the engine, on Tiptronic it cools the transmission, and Tiptronic cars tend to score sooner. Injectors serviced or new around 75,000 miles, good fuel, fuel trims checked every service, misfires fixed right away. On the 9A1, no full throttle until oil is at least 160 F.
On these engines I check for bore scoring before anything else. Before you buy the car, and before you put money in IMS bearing, clutch or anything big. New IMS bearing in scored engine makes no sense. If scoring is there, for sure it changes what you should do with the whole car. Find it later and you pay two times.
Also: Porsche service · IMS bearing · Ticking Macan · Porsche PPI