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I sometimes hear a knocking sound coming from the front of the car and I feel vibration at the bottom when this happens. It only happens when the car is rolling at low speeds. You can not hear the knock if the car is in idle or when you rev the engine.

Is this rod knock? I have a diesel car

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  • Welcome to Motor Vehicle Maintenance & Repair! Commented Jan 15 at 14:53

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It is hard to say from your description, but my initial hunch is No this is not rod knock. Your description kind of reminds me of lugging an engine.

Several factors lead me to this conclusion.

First, diesel engines make more noise due to their very high compression ratio (as compared to gasoline/petrol engines). When under load, the noise can be pronounced, making it a lot easier to hear. This is fairly normal for diesel engines.

Second, rod knock becomes more pronounced when revving the engine. You state the noise isn't there when you are revving it higher.

Some things to check to ease your mind would first be the oil pressure. If you have good oil pressure, this is a sign of engine health. As internal soft parts start to wear, oil pressure goes down, especially when the engine is warmed up. To figure out what the oil pressure should be, do a Google search using your vehicle year/make/engine and something should come up.

Along these lines, make sure you have enough oil and of the right type as prescribed by the manufacturer. Not having enough oil can cause weird noises.

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