2002 Subaru Forester, 2.5L engine rattles/knocks at start-up when cold. Noise goes away after engine heats all the way up to operating temperature. Then it runs great without any noise. Sounds like something on the outside of the engine in front (timing belt, water pump, belt idlers, alternator, Power steering pump or such). Doesn't sound like anything internal (pistons, conn. Rod, wrist pin, main bearings, etc.). Just drove it on a 500 mile trip without noise (except at start-up) and it ran perfectly. I tried an oil additive that is supposed to free up valve lifters but that didn't help. Have you heard of this before? Any idea what it could be?
Remove the serp belt and start the engine to determine if it is one of the accessories. (ONLY RUN THE ENGINE A FEW SECONDS TO SEE IF THE NOISE IS GONE) If the noise is gone, check the accessories for excessive play or a bad bearing. Make sure to check the water pump.
72 HEAVY CHEVY
November, 25, 2015 AT 8:36 AM
It is your timing belt tensioner. I did mine at about 80k, same noise, almost sounds like a knock at start up then goes away when warm. The tensioner is filled with hydraulic fluid and leaks out, causing it not to put the right amount of tension on the belt. When the engine warms up the fluid expands enough to make the sound go away. It took me a Saturday to change it, all belts (timing, and accessory) water pump, and oil/cam seals and plugs/plug wires. You should do all this at once as it (the engine) is all apart to get to the tensioner. It is an easy engine to work on and the timing belt is easy as well. I think I spent 2 to 300 hundred in parts, maybe less did it 2011. Still driving the car.