Pontiac Repair: Loud knock, pontiac grand prix, oil consumption

Question
i have a 2001 Pontiac grand prix 3100 sfi and when i start it it knocks until it warms up and then the knock goes away (at an idle) till i step on the gas!

Answer
Hi James.

This is a common issue on these engines. Without hearing it I'm guesing it sounds like a double knock like some shaking a can of spray paint? If so it's piston slap. The pistons are actaully chucking inside the engine and once the engine warms up the pistons grow in size from the heat and the chucking stops or is quieter. If the engine has a lot of miles on it it's pretty common. If it's a low milage engine GM actaully has a revised piston set for the engine to "reduce" the noise. Will it hurt anything? Not right away but over time yes you may notice increased oil consumption as well. It could also be a connecting rod bearing noise and that is not GOOD and it will not last long and will only get worse. Again without hearing it it's hard to say what it is.. Good luck :)