Boxster Tech

Engine & Transmission

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Air Filters

There have been many debates over the brand and types of air filters used, often between the OEM vs. K&N filters. This study compares the filration of various filters and their efficiencies and flow restrictions: Air Filter Test(link broken)

Coolant System

Coolant access is from the trunk. Leaks can happen due to a cracked coolant reservoir or hose, or via a worn coolant cap.

Since first introduced, the cap has been redesigned. The old style (left) can vent coolant at a lower temp/pressure than specified after some years of use. The new version (right) has been revised several times and will last many more years without dumping the coolant. New part number should be 996 106 447 04 and runs around $24.00 (2010 price)


Coolant Tank Edit

The plastic can develop a leak over time and must be replaced. Instructions on the tank replacement is here:

Boxster Coolant Tank Failure

Coolant Bleeder Valve O-Ring Replacement Procedure (from Porsche Joe) Edit


  • 1 999-707-370-40 Rubber o-ring
  • 1 999-707-371-40 Rubber o-ring


  • Ratchet 1/4" Sears No. 43187
  • 7mm socket 1/4" Sears No. 43503
  • 3" extension 1/4" Sears No. 43539
  • Regular blade screwdriver

1. With the engine cold, remove the oil and coolant caps. IMPORTANT: The engine MUST BE COLD to prevent the possibility of scalding when removing the coolant cap. 2. Remove the plastic cover to access the bleeder valve. You can carefully pry up the cover using a regular screwdriver. You should see condensation on the underside of the cover and/or dried coolant around the bleeder valve. The bleeder valve is not the problem unless you have one or both of these symptoms. 3. Put the oil and coolant caps back in place. This is IMPORTANT because it prevents you from dropping a bolt or o-ring into one of the openings. That would be a bad thing! 4. Lift the metal ring of the bleeder valve from the horizontal position (closed) to the vertical position (opened).


5. Remove the 8 bolts that secure the bleeder valve to the bleeder valve housing and coolant tank. Lift the bleeder valve from the housing.


6. Remove the bleeder valve housing by pulling straight up. This is a very tight fit. I had to use a regular screwdriver to carefully pry up the housing before I could remove it. Once you “break it loose” it lifts out easily.


7. With the housing removed you will see the two o-rings on the top of the coolant tank. I sprayed some silicone lubricant on the new rings before installing them (yea, yea, yea, I know, silicone lubricant accelerates the deterioration of rubber but that’s what I had available at the time). The lubricant will help keep the rubber o-rings from sticking during assembly. Instead of silicone lubricant you could coat the new o-rings with a thin coat of liquid soap or even use something like Vinlyex. Remove the old o-rings and install the new ones.

Small O-Ring


Large O-Ring (old one from "brand new tank" on left, real new OEM Porsche right)


Both O-rings on the bleeder valve top


8. Install the housing making sure the bolt holes line up properly. 9. With the bleeder valve still in the open position, install it on the housing. 10. Install the eight bolts (Hint: when starting a screw or bolt, use your fingers to turn it counterclockwise while gently pressing on it until you feel it “pop” into place then turn it clockwise to tighten it. If you do this each time you will never miss thread a screw or bolt again.) Be careful not to over tighten the bolts. I could not find torque specifications in the shop manual. If your problem continues then you may have to come back later and apply a little more torque.


Be very careful here or this could happen to you and you will need a whole new tank if you break the bolts.


11. Close the bleeder valve (move the ring from the vertical position to the horizontal position.)


12. Remove the oil and coolant caps. 13. Install the plastic cover. 14. Install the oil and coolant caps being careful not to miss thread the coolant cap. 15. Go for a nice long test drive.

Random Pictures of Parts

Difference in ring size


Top cap


Cap + valve base


Dirty parts


MAF Sensor

Mass Air Flow Sensors (MAFs) measure the amount of air, compensated for density, that an engine takes in to determine the proper fuel mixture. They can become dirty and affect the idling and performance of the engine, and they also can fail for electrical or mechanical reasons, unrelated to any visible contamination. Before replacing a MAF, many mechanics recommend cleaning the sensor to see if that corrects the issues. The MAF is accessed through the top engine access cover.

Here is a message thread on the topic, with pictures.

MAF Troubleshooting

Troubleshooting tips for Boxster/996 MAF Sensor
The MAF sensor has 5 pins labeled 1-5:
1. Temperature Sensor
2. 12v Supply Voltage
3. Ground
4. 5v Reference Voltage
5. Output Signal

The Output Signal ranges from 0-5v. 0v = No air flow, 5v = maximum measurable air flow. If the engine is off the Output Signal should read 0v. If it reads above 1v with the engine off it is most likely defective and needs to be replaced. I have seen them read 7v. The reading should increase with RPMs.

The Service Manual states the sensor should read:
Engine running at Idle = 0.55v (approx)
Engine at WOT [Wide Open Throttle] = 4.5v (approx)

MAF Cross Reference Chart

(Posted on by Stephen in VA, Monday, 20 June 2005)
I found this incomplete chart for MAF sensors (there were three EGas revisions making it tricky to get the right one) when I needed to replace the sensor in my 2000 2.7L, and figured I'd fill in the blanks on the newest sensor part numbers for anyone that needs a cross reference. They're about half the dealer cost if you buy them online and they're identical Bosch OEM.
996 606 120 00 - original sensor- 1997 Boxster / 0 280 217 007
996 606 123 00 - original sensor- Bosch PN B3130-70627 formerly B3130-116456
996 606 124 00 - update 1 - Bosch PN B3130-128499
986 606 125 00 - update 2 - Bosch PN B3130-149265
986 606 125 01 - update 3 - Bosch PN B3130-160651 / 0 280 218 055

Rear Main Seal (RMS) leak

The seal between the engine case and the crankshaft leaks oil in some percentage of Boxsters. To date the factory has attempted several fixes, however the problem persists. Repair under warranty has been done without question or cost to the car owner. Repair out of warranty is a different issue, with some warranty coverage offered at times. The symptom is a small amount of oil leakage easily detected on the garage floor under the engine. If this failure occurs, the owner of a used car should seek the warranty repair history from a Porsche dealer to determine if the repair had been previously attempted. This info may help in negotiating the "out of warranty" cost. If the car's mileage is high enough, it may also make $ sense to replace the clutch at the same time.

Engine Mounts

The rubber portion of Boxster front engine mount yoke are known to disintegrate over time and usage. Due to the design, there is no way to visually tell if the mount is broken without removing it. The symptoms of a broken mount include vibrations at startup and at specific RPMs (often in the 2100-2500 range), difficult, imprecise shifting and rough clutching. Some have suggested that the part lasts only 45,000 miles.

Broken engine mounts

More information, instructions and pictures:

Replaced the motor mount

Engine Mount and Fuel Filter update

DIY engine mount

Editor request: migrate the above information into this wiki for permanent archiving.


Some drivers swear by the reduced throw shifters. They're an inexpensive hack that makes a big difference in the feel of a car.

B&M Short Shifter

Official Site: B&M Racing (includes installation instructions)

You can purchase a DVD with 2 hours of instructions on installing a B&M Short Shifter at 9X9 Werks

Schnell Short Shifter


CEL Error Codes


Inserted inside the left side air intake is an oval-shaped plastic tube with a cup to prevent foreign bodies from entering the engine's air intake system, called the snorkel. The most-often noted problem is cigarette butts thrown by the driver which could be sucked into the air intake, causing a fire inside the system.

Some (many?) owners remove the snorkel which improves the Porsche engine noise that the driver hears, most notably under acceleration. The snorkel can be pulled out with moderate to hard tugging action, after removing the side vent assembly.

More info: Detailed instructions: [10 Minute Desnorkel Hack]

Porsche documentation: Removing and Installing the Engine Compartment Vent Vent Page

Recently it has been dyno tested to make +5hp and almost +3ft/lbs of torque on a Boxster S. It was a well known import tuner who ownes a shop and dyno that discovered this (Bisi Ezerioha of so it should be widely accepted as being proven.

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