My friend car, a 2003 civic EX D17a2 engine is knocking, but only when the motor is hot, and only between 2000rpm and 3000rpm. The engine is not knocking under load, only if you press the gaz pedale a little and you keep the same rpm.

When the car is cold there's absolutely no knocking sound. He put 10W30 oil instead of 5w20.

The oil pressure light doesnt stay on more than half a second when he start the car in the morning.

What is wrong?

 

pinging possibly, hopefully it's not pre-ignition. couple questions... what made your friend switch to 10-30? also, how is the weather up there right now?

 

It's still warm, in the 70's for the most part.

Are you saying that the car was fine and didn't knock before he changed to 10w30?

 

Hi, yes we are in summer now! No he always use 10w30, just to know if this can be the problem. anyways I think the motor will die soon

 

Sounds like you and your friend are expertise limited. I'd start with basic tuneup items. Plugs that are neglected can lead to misfires, same with bad coil boots. If the motor is not modified, then it's unlikely it's pinging, but more likely its misfiring.

Try basic tune up items then I'd suggest he take it to someone professional that can eliminate the issue, yet explain to him what happened so he can learn from it.