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Prior to the introduction of the Mezger engine, the 547 "
Fuhrmann" engine provided dry sump lubrication to ensure proper lubrication under all operating conditions. Engines including the pushrod horizontally opposed engine found in the 356/912 and inline and V engines found in front engine 924 and subsequent models, feature wet sump engines. Where dry sump engines store oil in an external tank and whose oil systems are generally more complicated, wet sump engines store oil in the bottom of the engine (sump). Wet sump engines are the most common type found in modern production engines worldwide because of simplicity.
The Mezger engine features a dry sump lubrication system where oil is stored externally. The oil tank also provides for oil de-foaming, ensuring oil supplied to the engine is thoroughly de-aerated under all operating conditions. Oil is filtered on the return (low pressure side) prior to entering the oil tank with a full-flow filter (no internal bypass). On 993 models, a secondary oil filter is used to protect the hydraulic lifters from fine particulate matter.
In the Mezger engine, the pressure side of the oil pump feeds all the main and rod bearings, chain tensioners (on models with hydraulic units), camshaft spray bars (and hydraulic valve lash adjusters, aka lifters in the 993), and piston squirters.
Piston squirters help to cool the piston and also lubricate the cylinder bores.
The scavenge side of the oil pump, which resides in the bottom of the engine and is driven off the intermediate shaft, which has oil-fed plain bearings on both ends, returns oil from the crankcase to the external oil tank or sump.
On models without engine mounted oil coolers or those with front or fender mounted oil coolers, an external oil thermostat ensures rapid engine oil warmup. A thermostatic switch is used on models with supplemental oil cooler fans to further assist with oil cooling.
The factory service interval for primary engine oil and filter was every 15,000 miles along with the 993's secondary filter every 30,000 miles, however it is current practice to change these filters every six months or 5,000 miles. For cars in storage during winter months, a single service prior to storage is also acceptable to ensure the engine is stored with clean oil.
With the introduction of the Boxster in 1997 and subsequently the 996 in 1999, Porsche made many changes to the engine including, but not limited to, switching to an "Integrated Dry-Sump" Lubrication System without an external oil tank, like found on the 993 and earlier models with the Mezger engine. Oil passages are cast into the crankcase, providing supply and return of oil. Pressure is provided by a single stage oil pump driven directly off the intermediate shaft that draws oil out of the sump via the oil pickup. Since there are no oil return tubes like in a Mezger engine, scavenge pumps are fitted to the cylinder heads to return oil to the sump via oil return tubes also referred to as "swirl pots" to de-foam engine oil. Later 987 and 997 models use an "oil slinger" to de-foam oil as it discharges oil onto the sump walls. To combat crankcase windage issues associated with wet sump engines, Boxster, Cayman, and 911 models are fitted with an air-oil separator (AOS) that applies a vacuum to the crankcase and separated oil mist from air, which is returned to the sump via drain tube and cleaned air gets routed to the engine air intake.
Where later air-cooled models used external oil coolers with an external thermostat to ensure proper oil temperature and rapid warm-up, Boxster, Cayman, and 911 models feature a heat exchanger located on top of the engine which warms up the oil with cross-flow of engine coolant through the heat exchanger.
Although special models like the 3.6 X51 in 2004 came fitted with additional oil scavenging in the heads and a special oil baffle to improve oil supply under increased G-forces, referred to as an "X51 baffle", additional steps should be taken to improve oil system and AOS performance to ensure proper lubrication if tracking your Boxster, Cayman, or 911.
Just like with an air-cooled Mezger engine, over-filling your engine can lead to smoking, elevated oil temperatures, oil foaming, and increased oil consumption. On early Boxster and 996 models, a dipstick is provided to positively measure and set oil level, but eventually that was abandoned for an electronic oil level sensor. Where oil level is measured running and at full operating temperature on a level surface, the Boxster, Cayman, and 911 from 1997-2008 (without Mezger engine) need to be measured differently.
Oil change intervals for the Boxster and 996 originally were two years or 24,000 miles, but has been reduced significantly. Like with aircooled models, many industry professionals recommend oil and filter changes every six months or 5,000 miles, but if unsure about lubricant choice and intervals, used oil analysis can help owners make sure they are doing right by their engines.
Starting in 2009, Porsche introduced the 9A1 engine with an improved "Integrated Dry Sump." 987.2 and 997.2 models feature a more robust oil control and a variable demand oil pump that ensures adequate oil supply under most operating conditions, eliminating oil system issues experienced with the prior generation of Boxster, Cayman, and 911 models from 1997-2008 (not including GT3, Turbo, or GT2 models with a dry-sump Mezger engine). These engines have proven themselves as durable as prior Mezger engines for track use with proper maintenance, enough so that Porsche replaced the Mezger engine in the Turbo and GT models with the 9A1 engine.
Charles Navarro
LN Engineering LLC
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