I have a knocking problem. When I start my truck, there is a knocking sound from the engine. It gets worse when the gas is depressed or when the engine is under load. It is loud enough to be heard inside the house. Odd thing, the knocking is 90% gone after the engine is warmed up. It is still there, but can hardly be heard. What could it be? I put Restore engine treatment last oil change, about 800 miles ago, could that be a cause? I dont remember if it was there before the change. The engine has had synthetic running since the day it was new. It is quite embarassing when driving down the road. Any help??

 

It sounds like you have a cracked piston or a bad wrist pin. When the engine warms up the engine parts become tighter or swell from the heat. This is why it seems to calm down when warm. A rod bearing would more like the opposite of what you described.

 

Is this a serious problem? I mean, should I worry about a serious breakdown anytime soon?

 

Yes, it could knock for ever and not completely fail or it could give up at any time. Theres no way to determine how long it will run like. I had a buddy that drove his car for a long time with a bad wrist pin.

 

If it is a rod it will have a double knock while a piston slap is a single flat sound that improves with increasing engine temp and may run for 100,000 mi. without a failure , If it's a wrist pin the noise is a single sharper sound and improves with temp and may run a very long time, (the operative word is may) I have a 302 in a truck with over 75,000 mi on a very loud piston slap.If thats the noise it's expensive to fix,bore cyl. and replace piston and rings.

 

Sounds like its the wrist pin. My truck has 242,035 on it and runs fine accept for that. It doesnt seem to get any worse each time I drive it, so Ill just take real good care of it and not abuse it. Thanks for the help, not that its good news, but at least I have an idea of what it is. thanks again.

 

Maybe the main bearings too. As mains fry out, they get loud when cold, the more damaged, the more noise and longer too. Then again maybe not......I've never heard, or heard of mains making as much noise as your saying.