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Porsche 911 (996) 3.4 / 3.6buyer's guide

1998–2003

The faults this model is known for, what they tend to cost in the UK, and what a service history has to show before any of them counts as covered. Researched from the sources shown, and open to correction.

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Type the registration for a free summary of its MOT history, read against the faults below. No sign-up.

If none of it were documented

£10,750–£24,600

Across 8 costed items.

This is a ceiling, not a forecast. A report on a specific car counts only the items its paperwork does not already cover - a folder showing the clutch done last year removes that line entirely.

Known faults

IMS (intermediate shaft) bearing

£1,500–£2,500

The bearing supporting the intermediate shaft, which drives the camshafts, can fail and take the engine with it. It is the most famous failure in modern Porsche ownership and the least evenly distributed: the risk depends on which bearing the car left the factory with, not on how it has been driven. A retrofit to an uprated bearing is the accepted fix and is normally done with the clutch, because the gearbox has to come out either way.

A retrofit is commonly quoted around £1,500 to £2,500 in the UK depending on which bearing is fitted and whether the clutch is done at the same time. A failure that reaches the engine is a rebuild, and rebuilds on these run well into five figures.

Typically bites

Not mileage-driven in any reliable way. Failures are reported across the range, which is why the retrofit is treated as insurance rather than as a repair at a set interval.

Verified against 3 published sources.

Cylinder bore scoring

£6,000–£15,000

The piston wears through the cylinder wall from the bottom up, letting oil past into the combustion chamber. The car burns oil, smokes, and eventually needs the engine apart. Unlike the IMS it gives warning, and unlike the IMS there is no preventative fix - only inspection and then a rebuild.

A borescope inspection is around £150 to £250 in the UK and is the cheapest money anybody spends on one of these cars. The repair is a rebuild with resleeving and oversized pistons, quoted in the several thousands and upwards depending on what the strip reveals.

Typically bites

Reported across 1999 to 2008 engines. Short journeys and long oil intervals are both implicated, which makes the service record relevant rather than incidental.

Verified against 3 published sources.

Rear main seal (RMS)

£600–£1,200

The seal between engine and gearbox weeps oil. On its own it is a nuisance rather than a catastrophe, but the labour is the same as the IMS job because the gearbox has to come out, which is why the two are almost always quoted together and why a car with a recent clutch and no RMS invoice is worth a question.

Little on its own beyond the seal, and several hundred to over a thousand in labour if done alone. Done alongside a clutch or IMS retrofit it adds very little, which is the whole argument for doing them together.

Typically bites

Age- and use-related. A dry car at twenty years old has usually had it done, whether or not the seller knows.

Verified against 2 published sources.

Air-oil separator

£250–£600

A failed separator lets oil into the intake, producing clouds of white smoke and a car that looks catastrophically unwell while being cheap to fix. Worth knowing precisely because the symptom is so alarming: it is one of the few frightening things on this car that is not expensive.

A few hundred pounds fitted at an independent, and one of the cheapest jobs on the car.

Typically bites

Wear-related, commonly reported once these cars pass fifteen years old.

Verified against 1 published source.

Coolant expansion tank and water pump

£400–£900

Plastic cooling components go brittle with age and heat cycles. A tank that splits or a pump that fails dumps coolant quickly, and an air-cooled reputation does not help a water-cooled engine that has run hot.

Both are routine independent jobs, in the low hundreds each, and are usually done together on a car of this age.

Typically bites

Age-driven rather than mileage-driven. Most cars are on at least a second pump.

Verified against 1 published source.

Ignition coil packs and spark plug tubes

£400–£900

The coils sit close enough to the exhaust that the heat cracks them, and the plug tubes weep oil onto the plugs from below. The two arrive together and present as a misfire. Specialists upgrade to the later 997-style coil and do the tubes at the same time, because the access is the same and doing one twice is the expensive way.

A full set of six coils and plugs with the tubes is a mid-hundreds job at an independent.

Typically bites

Driven by heat cycling. Commonly quoted as a five-year item rather than a mileage one.

Verified against 2 published sources.

Clutch and dual mass flywheel

£1,200–£2,400

Ordinary wear with an expensive neighbour. The flywheel goes with the clutch because the labour is identical, and a leaking rear main seal will destroy a new clutch quickly if it is not addressed at the same time. The gearbox is out for all three, which is also the access for the IMS bearing - so a clutch invoice that mentions none of the others has paid for the hard part of four jobs and used it for one.

A clutch and flywheel at an independent is a four-figure job. Adding the seal and the bearing while the box is out costs comparatively little.

Typically bites

Use-driven rather than age-driven.

Verified against 2 published sources.

Front control arms, bushes and drop links

£400–£1,100

The front suspension wears in a way that is felt rather than heard at first: vague steering, uneven front tyre wear and an alignment that will not stay put. Squeaks from the tie rods and control arms are the audible stage. Cheap by the standards of everything else on this page, and the item most often left for the next owner.

Independent work in the mid hundreds per axle depending on how much is replaced at once.

Typically bites

Age- and mileage-driven, and universal on cars of this age on original parts.

Verified against 2 published sources.

Service interval

Every 12,000 miles or 12 months, whichever comes first.

Specialists work to an annual oil change on these regardless of mileage, and shorter than the factory schedule. Oil condition is implicated in both of the expensive failures above, so a folder showing two- and three-year gaps between changes is itself a finding.

The interval is here so a report can do arithmetic rather than form an opinion: last recorded service, current mileage, today's date. Whether a car is overdue is a sum, and sums should not be able to hallucinate.

What to check on the day

Written to be read standing next to the car, with the folder open.

  1. Ask directly whether the IMS has been retrofitted, and ask to see the invoice rather than accepting the answer.

  2. Ask whether it has ever been borescoped, and if so when. A seller with a recent report will produce it immediately.

  3. Cold start it and watch the exhaust for the first thirty seconds from outside the car.

  4. Check the oil level and condition yourself, and ask when it was last changed.

  5. Look for oil misting around the bellhousing seam where the engine meets the gearbox.

  6. On a 2000 to 2005 car, establish which bearing it has. On a 1998 or 1999 car the risk is genuinely lower and the seller may not know that.

What this research does not know

  • IMS failure rates quoted here come from specialist retrofit suppliers, who see failed engines rather than a representative sample. Treat the percentages as the shape of the risk rather than as an actuarial figure.
  • Bore scoring repair costs vary more than any other figure in this library, because the band depends entirely on what a strip reveals. The low end assumes resleeving; the high end assumes a full rebuild.
  • Several sources price in dollars. GBP bands here are UK independent specialist rates rather than conversions.
  • Turbo, GT2 and GT3 variants use different engines and are outside this profile.
  • Scoped to 1998-2003 although the 996 ran to 2005, because the 997 shares the 3,596cc capacity from 2004 and the cache key cannot separate them. A 2004 or 2005 996 is answered by the 997 profile, which shares most of this story.

Last reviewed on 22 August 2026. Cost bands are indicative UK independent-specialist rates, not quotes.

Now find out which of these the car you're looking at can actually prove.

Photograph or upload the seller's folder and every invoice is read, checked against the official mileage record, and matched against the list above - so the total you get is what this car has no evidence for, not what the model might cost in general.

See a full worked example