"Engine" ? Noise

Asked by Jul 20, 2017 at 07:55 PM about the 1990 Porsche 911 Carrera 4 AWD Convertible

Question type: Maintenance & Repair

1990 964 Carrera 4, 28,000 original miles. Car only driven on rare occasions,
old but low mileage oil. Started car, felt a little strange. Initial thought felt like
some light "back pressure". Car started, ran for just over 1-second, metal on
metal? knock, ran fine briefly, I shut off. Started again and repeat of noise
sequence. Didn't knock when last driven, knock appears to be random not
based on cylinder operation. Haven't tried to start again! Your thoughts would
be appreciated, thanks.

1 Answer


Low mile cars can be a problem from non-activity. A sitting car is not a Porsche Design-In. Bathing in fresh hot oil is a design. Because, while sitting, oil drains off parts. Every start is a "cold" start introducing oil to parts. Old low mileage oil will accumulate moisture, this a normal PROBLEM. To correct the PROBLEM, car should be run and Oil Temps must reach 220 degrees on every start to burn off impurities. Low mile aging cars CREATE the above problems. Along with have 30K, 40K, 50K service hit all at once. Slight knocking and rattling can occur on a "cold" start. The noises should reside quickly as oil pressure reaches normal operating pressure. Do you have an oil pressure gauge to monitor? Random knocking is not a good sign if it is internal. Sounds like a visit to a certified mechanic for a check up. In the future. Drive the beast! Preserving cars can be more problematic than high miles. I raced my 964 engine for over 200 Race hours. Racing is constant Full THROTTLE! Full Brake! Full Throttle! And, 3 years after selling the car. The engine still performs at peak HP. This is what these cars were built for. I kept Fresh oil, and oil temps under 250 degrees during racing conditions. Hope this helps. Good luck!

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