What would cause a knocking noise when the engine is cold?

Answer 1

• My first guess is the neighbor's cat trying to get out from underneath the hood. However, if you see no hair, I would question if the oil is getting up to the valves efficiently. I can do a little research, but I would need the engine size, how often you change the oil, what weight oil you use (5w30?) and does the noise come from above the engine or below? Is the noise a heavy knock or more of a tapping? Post a follow-up here, and I'll try to help.
• Replace the PCV valve. I've had similar problems with a Saturn, I even had to replace a whole motor because it consumed too much oil. I discovered that the new engine was doing the same thing. After replacing the PCV, everything was back to normal.
• There is a TSB about cylinder head gaskets leaking on these cars. This kind of leaks can have various symptoms including those that your having.
• Sounds like car has been overheated and has a collapsed piston skirt. This will cause piston slap until piston heat up and expand.
• Synthetic oil is too thin for a used engine. You should use a straight weight oil, like 30W. Sometimes a flex plate on the transmission will develop cracks and make noise when cold (been there). If the oil pressure is low, there could be a knock, which synthetic oil can cause in an older engine because it is too thin. If there is a check valve in the oil filter or a cheap oil filter, it could be letting the oil drain from the oil pump.
• A cold knock is usually caused by piston to cylinder wall excessive clearence. sometime on a quick rebuild .even with spread the piston skirt. you will get a knock. a low down in the engine heavy knock is main bearings. a fast knock is the rods bearing our a cracked piston. a tapping upper niose is valve lifts in a hydraulic lifter engine. in a solid lifter engine you cah adjust the noise out. some time you will have change the rocker arms our resurface. a bearing knock get louder with temperature. pistons expand with tempiture quiting the noise you need any experinced mechanic to tell you what is wrong, in person. long distance diagnose is hard. hold it up to the phone and let me hear it turbo joe.
• It sounds like you're transmission is beginning to collapse. Is it an automatic? If so, you might want a professional mechanic to examine this IMMEDIATELY. If you don't not only will it become undrivable but it could eventually affect the rest of the engine like a series of bombs taking out individual parts. I had a experience very much like what you're describing with a 95 Buick Skylark and by the time it was looked at 2/3 of the engine was destroyed. Good luck!
• Sometimes if you do not change your oil and the oil breaks down into sludge because you didnt change your oil in time you get whats called a stuck lifter and it can cause a loud rocking slapping noise they have engine cleaners that are on the market some aren't so good so choose wisely.
• Oil... and really watch what oil you use... newer hondas and other foeregn jobs have small ports for oil circulation.... well for the oil to return to the bottom... that could cause rod knock... and since the oil isn't going back down right away to get pumped it would cause the rockers to rattle a bit... but when it warms up finally the oil will flo better.... cant remember which company... but if you popped the motor by using the wrong oil they wont cover a damn cent.... even if its only 3 4 months old.
• Ok there right but if u had bad rings 1 the car would smoke and 2 the car wouldn't have power now i had a 94 thunderbird with a 3.8 and i got the same knocking or tapping and it was a ristpin which is located on the piston if you didnt know now most likely if its a tapping noise from the top of the engine it is normally a callapsed lifter which happen you wont lose power and it wont smoke but to cure the noise use a heavy weight oil such as 20/50the tap could also come from rockers if you have a cloged push rod which happens over age it will cause a lack of oil to the top if the engine process of elimination check the rockers make sure there tight and to torque sequence.
• I've had 2 Hondas, and still currently have one of them. I don't think you have anything to worry about. I was reading all of these responses and laughing...The cars run at a higher idle, which is computer driven until the engine is warm. The Vtec kicks in at higher idles (usually 4000+ rpms) but it is also driven by oil pressure. Since the oil is more viscous at colder temps, and the car is running at higher rpms, your are simply hearing some valve noise. Chances are the valves are perfectly fine. Once warm...does the car run ok, I'm guessing yes. The guy that answered saying it's the Transmission...c'mon you can't compare a Buick to a Honda!
• It's because oil, even a multi-grade like 5w30 is still too thick to flow efficiently when cold. Auto manufacturers choose an engine oil "weight" for OPERATING temperatures, not for when the engine is cold. Even a 5 or 0w oil, when cold, is thicker than a 40w at operating temp. This causes restriction in the small orifices in parts such as lifters, which is the most common source of engine tick when an engine is cold. BTW, cold is defined as a temperature less than the oil's effective operating range, 180-250F for example. That said, an oil at room temperature is still too thick. Google it.