2002 Saturn L300 Knock on top of engine

MESSENGERJJJ

MEMBER
2002 SATURN L300
6 CYL
RWD
AUTOMATIC
167,000 MILES

We had a cold spell and the car didn't want to start. Had recently had oil change 2 weeks prior. After it started and driving, the engine started knocking and it won't go as fast. No prior problems. It has the correct amount of oil and still has the correct amount of antifreeze. Am puzzled. What could this be.

Don't mind donating for diagnosis, but would prefer to mail check or money order. Thanks in advance

2 Replies

CARADIODOC

MECHANIC
33,727 POSTS

Both of your observations are wide open to interpretation. You have to describe the knocking, and "won't go as fast". My 25-year-old Grand Caravan doesn't go as fast as when it was new because it has well over 410,000 miles on it. Do you mean it takes a few seconds longer to get to 60 mph, or it struggles to get to 30 mph?

Do you have an oil pressure gauge on the dash? If not, having the pressure checked with a mechanical gauge is the first step. If it is real low, suspect worn engine bearings. The resulting knocking will be plenty loud to hear a long way off. That will also be detected by the knock sensor, and as a result, the Engine Computer will retard ignition timing in an unsuccessful attempt at stopping the knocking. That reduces engine power noticeably.

Did you determine why the engine didn't start? If it was spark-related, raw fuel would have run into the cylinders, past the rings and into the oil. Oil diluted with gas will destroy the engine bearings very quickly, as in less than a hundred miles.

Some other causes of knocking can be much less serious, but still, if the knock sensor detects it, engine power will be reduced.