ENGINE AND IMS BEARING
996 Carrera 4S power comes from a 316bhp version of the familiar 3.6-litre flat-six, with maximum output developing at 6,800rpm. While both this engine and revised headlights (so long, fried eggs!) feature on every 996 Carrera built in and after 2002, only the Carrera 4S has the hardware and hips to claim a legitimate relationship to the Turbo.
Cracked cylinder heads were a problem on some early 996s. Reading forum posts may lead you to conclude there has been an epidemic of cracked cylinder heads and liners on M96 engines. In reality, the issue is relatively rare and the prominence of horror stories published online is due to unlucky owners venting after being on the receiving end of large repair bills. Unless you have access to specialist equipment, the problem is very difficult to spot in its early stages. Given the price of a replacement engine, it's well worth investing in a borescope inspection before buying a C4S, thereby helping you to establish if expensive failure is imminent.
A claim heard often is that cracked cylinder heads and liners occur between 25,000 and 50,000 miles. In truth, the problem can strike on higher mileage cars, too. A more relevant piece of information is to keep in mind early 3.4-litre engines have proved much more prone to this problem than the post-2001 3.6-litre units.
The rear main oil seals (RMS) were a weak point on Porsches of this era and leaks are not uncommon. Although the seal itself is an inexpensive part, labour for the work can be costly, primarily because the seal is very difficult to access. If you spot an oil leak on the C4S you plan to buy, ask a Porsche specialist to take a look. A leak doesn't always mean the RMS needs to be replaced immediately — the work can often be delayed until a bigger job (such as changing the clutch) needs to be carried out, but it's certainly something to note as likely to need attending to in the future.
One of the most serious issues on the 996 flat-six is failure of the factory-fitted IMS bearing, which can lead to catastrophic engine problems. An IMS is used to transfer power between crankshaft and camshafts. At one end of the IMS sits a plain bearing, while the other end is fitted with a ball bearing. Three different types of ball bearing were used during M96/M97 production, starting with a dual-row ball bearing in 1996. A smaller single-row ball bearing was introduced three years later. The IMS and its plain bearing are submerged in oil during normal operating conditions and the ball bearing is filled with grease protected from the engine oil by a seal.
Differences in manufacturing tolerances can result in seal failure and material mixing with the grease, thereby wearing out the bearing, resulting in failure. If the bearing lasts for several years, however, there’s a good chance it will continue operating without fault long into the future.
A misfiring engine (or one sounding rough when running) may be a sign of problems with the ignition coil packs. Over time, heat from the engine and exhaust can cause the coils to expand and the insulation to crack. The only solution is to replace the parts. Thankfully, it will be relatively inexpensive to have the work completed by an independent Porsche specialist. The packs are likely to have to be replaced several times during the car’s lifetime.
The coolant radiators in the front bumper (and the air-conditioning condensers located directly behind them) are susceptible to stone chips and corrosion resulting from dirt, salt and leaves coming in through the air scoops. In an ideal world, the debris would be regularly cleaned away, but most 996 owners never attempt it, leaving plenty of time for damage to develop between services. Suspect radiators and/or condensers will need to be replaced to avoid overheating and the loss of air-conditioning.