Data from a Rennlist owner thread, read in full on October 27, 2026. Last post counted: July 22, 2024.
The short answer
- We read all 714 posts in the Rennlist poll thread that asks 997 owners whether their cylinders scored, and counted 98 first-hand owner reports.
- 50 owners reported scoring, 43 reported none, and 5 had another cylinder or engine failure.
- Cylinder 6 was named in 22 of the 29 scoring reports that said which cylinders were affected, far more than any other.
- 997.2 owners reported scoring in 6 cases, so the later engine is not immune, but that is too few reports to compare the generations.
- These are owners who chose to post. People with a problem post more, so the share of scoring reports here is not a failure rate.
In April 2016 a Rennlist member started a poll thread asking 997 owners to report whether their cylinders scored, with year and generation. It ran to 48 pages by mid-2024.
This page pulls the owner reports out of that thread, counts them, and links each finding back to the post it came from. Thanks to the Rennlist members who posted about their cars and shared borescope photos. The thread is here: Poll: Scored cylinder failure for your 997, Y or N?.
It covers the Carrera, Carrera S, Carrera 4, Carrera 4S, Targa 4/4S and Cabriolet. The 997 Turbo, GT2 and GT3 use a different engine with different cylinders and were left out.
Which 997 has which cylinders
Porsche fitted the 997 Carrera with a 3.6-litre flat six and the Carrera S with a 3.8, and brought new direct-injection engines with the autumn 2008 update. LN Engineering says the 2005 to 2008 M96/M97 engines use Lokasil cylinder bores, and the 9A1 used from 2009 returned to Alusil.
| Model years | Generation | Engine | Cylinder bores |
|---|---|---|---|
| 2005 to 2008 | 997.1 | M96 3.6 (Carrera) / M97 3.8 (Carrera S) | Lokasil |
| 2009 to 2012 | 997.2 | 9A1 3.6 / 3.8 (direct injection) | Alusil |
LN Engineering says the 3.6 and 3.8 versions of the M96/M97 are the most affected by scoring, and that Alusil engines like the 9A1 can also score, though in its experience at much lower rates.
Sources: Porsche Newsroom, sixth-generation 911 engines; LN Engineering, what is cylinder bore scoring.
Owner reports by generation
| Generation | Owner reports | Scoring reported | No scoring | Other cylinder or engine failure |
|---|---|---|---|---|
| 997.1 (2005 to 2008) | 75 | 39 | 33 | 3 |
| 997.2 (2009 to 2012) | 13 | 6 | 6 | 1 |
| Generation not stated | 10 | 5 | 4 | 1 |
| Total | 98 | 50 | 43 | 5 |
By model year
| Model year | Owner reports | Scoring reported | No scoring | Other failure |
|---|---|---|---|---|
| 2005 | 24 | 13 | 10 | 1 |
| 2006 | 25 | 11 | 13 | 1 |
| 2007 | 11 | 4 | 6 | 1 |
| 2008 | 5 | 3 | 2 | 0 |
| 2009 | 6 | 3 | 3 | 0 |
| 2010 | 1 | 1 | 0 | 0 |
| 2011 | 1 | 0 | 1 | 0 |
| Not stated | 25 | 15 | 8 | 2 |
About half of the reports describe scoring, mostly because owners with a problem are more likely to post. The poll widget shows a lower share: on October 27, 2026 it showed 146 "yes" and 543 "no" votes for the 997.1, and 18 "yes" and 305 "no" for the 997.2, from 1,012 voters. Those votes are unverified and cannot be tied to specific cars.
By engine
Among 997.1 reports where the engine was stated or could be inferred from the model, owners reported scoring on 27 of 52 cars with the 3.8 (M97) and 7 of 10 with the 3.6 (M96). The 3.6 sample is too small to read anything into the difference.
Mileage
Scoring reports gave a mileage in 42 cases. The median was 60,000 miles, from 6,000 to 135,000. Mileage is when the owner found the scoring, not when it started.
Which cylinders owners named
29 of the scoring reports said which cylinders were affected. Some named 1 cylinder, others several, and 5 said all 6 showed scoring.
| Cylinder named | Scoring reports naming it |
|---|---|
| Cylinder 1 | 7 |
| Cylinder 2 | 6 |
| Cylinder 3 | 7 |
| Cylinder 4 | 13 |
| Cylinder 5 | 11 |
| Cylinder 6 | 22 |
Cylinder 6 came up in 22 of those 29 reports. Cylinders 4, 5 and 6 together came up far more often than 1, 2 and 3. That matches LN Engineering, which says scoring on these engines is most common on bank 2, cylinders 4 to 6.
Warning signs owners described
These are owner reports, not a diagnostic guide. Each links to the post.
- One sooty tailpipe. Owners often noticed more soot on the left or driver's side, as in this low-mileage 2005 and this 2006 Carrera S. LN Engineering says a sootier driver's side outlet matches bank 2, and also that uneven soot can just mean the engine is running rich.
- Rising oil use. Owners described consumption that crept up over time, for example about a litre every 900 km before diagnosis and a quart every 1,500 miles that climbed sharply around 89,000 miles.
- Smoke at cold start. Mentioned alongside oil use in several reports, such as this 3.6 with scored cylinders 4 and 5.
- Ticking or piston slap. Several mentioned a tick that would not go away, such as this 2005 C2S that started ticking 1,000 miles after purchase.
- A misfire or fouled plug, often on cylinder 6. For one 2008 owner, a wet number 6 plug at a major service led to the scope that found scoring. Another got a misfire code on cylinder 6 and a badly fouled plug.
- No symptoms. A good share of owners found scoring only because they went looking, like this 2007 C2S with low oil use and clean tailpipes and this C4 that was scoped during unrelated service.
How owners checked
- Borescope. The most common check in the thread. Some scoped through the spark plug holes during a plug change, some had a shop drop the sump to look from below. One owner noted his clean result was from the top side only and planned a look from underneath. LN Engineering calls a borescope the most direct way to confirm scoring and says looking only through the plug hole can miss early scoring lower in the bore.
- Oil analysis. Results were mixed. One owner with light scoring in all cylinders got a normal report. Another saw only a slight uptick in aluminium once scoring was already present. LN Engineering says oil analysis supports a diagnosis but should not be used alone.
- Leak-down and compression tests. Mentioned now and then, but some owners who later found scoring had normal results first, like this track-driven 2005 C2S.
What owners did about it
Of the 50 owners reporting scoring, 17 chose a rebuild (re-sleeving, Nikasil-type coatings or a bigger-displacement build), 10 fitted a replacement engine, 9 kept driving and watched it, 1 sold or returned the car, and 13 did not say.
Owners who kept driving tended to have mild scoring and no symptoms, like this 2007 C4S at 23,000 miles. One new owner found a scored cylinder on an engine that had already been re-sleeved.
What other forums report
The counts above come only from the Rennlist thread. Other forums ask different questions about different cars, so we kept them out of our counts and tables. What follows are owner votes and a shop opinion.
A PistonHeads poll. A PistonHeads thread started in September 2011 asks "Has your 996 or 997 engine had a major rebuild?" The poll is open to anyone, and the person who started it said it is multi-answer.
| PistonHeads poll answer | Votes |
|---|---|
| No | 511 |
| Yes, because of scored bores | 95 |
| Yes, because of the IMS | 66 |
| Yes, because of D chunk failure | 9 |
| Rebuilt before purchase, not sure why | 46 |
| Have not bought one because of known faults | 189 |
As shown on October 27, 2026. 903 members polled. Voters can pick more than 1 answer, so the votes add up to more than 903.
95 voters said their engine was rebuilt because of scored bores, more than the 66 who said the IMS. The poll mixes the 996 and 997 and does not ask for model year or engine. PistonHeads is a UK site. Voters choose to take part, so the poll is not a failure rate.
A PPI shop on Pelican Parts. In February 2021 an independent shop that does pre-purchase inspections posted on the Pelican Parts forum that it had found scoring on a substantial number of 997.1s. It said the scoring was worse on bank 2, cylinders 4 to 6, and often left the left tailpipe carboned up. Many of those cars ran well, and some had a tick. The latest one it described had under 20,000 miles. That is one shop's view with no count. It agrees with the Rennlist owners, who named cylinders 4, 5 and 6 most often.
The 997.1 has a second well-known engine issue that the 997.2 does not: the IMS bearing. See what 419 owner reports show about 997 IMS failures.
What this data cannot tell you
- A failure rate. Owners chose whether to post, and people with a problem post more. Half of the reports here describe scoring. That does not mean half of 997s score.
- Whether the diagnosis was right. These are owner calls, often based on borescope images. One engine builder in the thread said about half the engines sent to his shop as bore scored turned out not to be. Owners in the thread often disagreed on whether light streaks in borescope photos count as scoring.
- When the scoring started. The mileage is when the owner found it. Many cars were only scoped years into ownership.
- What causes it. Owners debate oil, warm-up habits, fuel mixture, climate and track use. Too few gave enough detail to compare.
- A direct comparison with other forums. The PistonHeads poll mixes the 996 and 997 and does not ask for model year, and the Pelican Parts shop gave no numbers. Neither can be set against the Rennlist counts.
- 997.2 rates. 13 reports is far too few to say anything about 997.2 scoring rates.
How we counted
We downloaded all 48 pages on October 27, 2026 and read the posts. A report counted when an owner described the outcome for a 997 they own or owned. We left out second-hand stories, cars inspected for purchase but not bought, Turbos, GT3s, 996s, Boxsters and Caymans, and repeat posts about the same car. Owners who described light marks but said their engine was not scored were counted as no scoring, following the owner. Quoted text inside posts was removed before counting so the same report was not counted twice. Counts are a judgment call in places, and every row in our working file links back to its post. If you think we coded a post wrong, tell us and we will fix it.
The other-forum section is separate from our counts. None of its numbers are in any count or table above. We opened each page on October 27, 2026 and took the figures as shown that day.
Sources
- Rennlist: Poll: Scored cylinder failure for your 997, Y or N? (thread started April 2016)
- PistonHeads: Has your 996 or 997 engine had a major rebuild? (poll, thread started September 2011)
- Pelican Parts: 997.1 cylinder bore scoring (shop post, February 2021)
- Porsche Newsroom: sixth-generation 911 engines
- LN Engineering: what is cylinder bore scoring
- LN Engineering: how to bore scope for scoring
More on the 997
- Porsche 997.1 Carrera buyer's guide: what to pay and what to check
- 997.1 torque specs for common maintenance and DIY jobs
FAQ
How common is bore scoring on a Porsche 997?
No public data gives a reliable rate. In the Rennlist owner thread, 50 of 98 owner reports described scoring, but owners chose to post and people with a problem post more, so that is not a failure rate.
Can a 997.2 get bore scoring?
Yes, though less is known. 6 of the 98 owner reports in the Rennlist thread were 997.2s with scoring. LN Engineering says the Alusil 9A1 engine can score, but in its experience at much lower rates than the earlier M96/M97.
Which cylinder scores most often on a 997?
In the Rennlist thread, owners named cylinder 6 most often (22 of 29 reports that named a cylinder), followed by 4 and 5. LN Engineering says scoring on these engines is most common on bank 2, cylinders 4 to 6.
What are the signs of bore scoring on a 997?
Owners most often mentioned a sootier left or driver's side tailpipe, rising oil use, smoke at cold start, a persistent tick, and a misfire or fouled plug, often on cylinder 6. Some found scoring with no symptoms at all.
How do you check a 997 for bore scoring?
Most owners used a borescope, either through the spark plug holes or from below with the sump off. LN Engineering says the borescope is the most direct check and that plug-hole views can miss early scoring. Oil analysis, oil use and tailpipe soot are supporting signs only.