Exhaust hex nut for heat exchanger. Porsche 911/964/993 1965-98  ❭  99908500103

Exhaust hex nut for heat exchanger
OE Match exhaust hex nut designed as a direct-fit replacement fastener for the exhaust heat exchanger studs on classic Porsche 911 (1965–1998) engines. This hex nut secures the heat exchanger to the cylinder heads and exhaust studs, ensuring reliable fastening in the high-heat exhaust system environment.
Sold individually. 4, 5, or 6 required, depending on car model.

Fits:
Porsche 911 1965-89 (6 for both heat exchangers)
Porsche 964 Carrera 1989-94 (4 for both heat exchangers)
Porsche 993 Carrera 1994-98 (5 for both heat exchangers)
Porsche 993 Turbo 1994-98 (4 for both heat exchangers)

Diagram ref no 5

The hex nut is used in conjunction with the heat exchanger studs and exhaust system components to clamp the exhaust heat exchanger securely in place and maintain a sealed joint between mating parts.

The exhaust hex nut’s role may seem simple, but it’s critical to the integrity of the heat exchanger and exhaust assembly:
• Secures the heat exchanger studs to the engine block/exhaust flange
•  Maintains clamp force under thermal cycling and vibration
•  Helps prevent exhaust leaks at the heat exchanger interface
•  Resists corrosion and heat exposure typical of exhaust temperatures.

Proper fastening ensures that the heat exchanger - which routes exhaust gasses away from the cylinders and towards the muffler system - remains sealed and aligned throughout engine operation.

Function
•  Fastening: Threads onto the exhaust/heat exchanger stud to clamp components
•  Retention: Holds joint integrity under vibration and thermal expansion
•  Seal support: Helps maintain exhaust system seal and prevents leaks
•  Heat resilience: Engineered from heat-resistant material for exhaust applications.

Worn, rusted, or missing hex nuts can lead to loose exhaust joints, exhaust leaks, poor performance, and increased noise.

Although small, exhaust hex nuts play a critical role in maintaining proper heat exchanger sealing and long-term exhaust durability. Over time, exposure to extreme heat and exhaust gases can cause nuts to corrode, seize, lose clamping force, or break during removal, leading to exhaust leaks and compromised sealing at the cylinder head. Replacing them with OE Match hex nuts restores secure fastening, helps prevent leaks, protects surrounding engine components from excess heat, and preserves overall exhaust performance.

Exhaust hex nuts should be replaced whenever the heat exchanger or exhaust system is removed, if the existing nuts are corroded, seized, rounded, or damaged, or when exhaust leaks are detected at the heat exchanger interface.

Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.

99908500103

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