Hey guys,
I have a 1998 XC. I bought the car in poor running shape because of burnt exhaust valves. I have since fixed that and the car is up and running well. But after the car run for 10 minutes or so it develops a humming noise that is obvious at idle. I'm not sure if this is a common issue or what could be causing this. I looked at the normal suspects. I pulled the dipstick when the car was making a humming noise to see is possibly the PCV system was letting the crank case over pressurize, and that did not change anything. I thought maybe it was one of the accessories or idler/tensioner, so I took the serp belt off and started the car. The noise is still there. The car has a new timing belt, with new pullys and water pump...I hope that stuff would not be bad out of the box but I guess it could be. Any suggestions or ideas on what could be making this noise? I find it odd that the car sounds normal while it is cold but once it gets warms it makes a noticeable humming noise. The only code I am throwing is P0442, so I will look at the J hose on the charcoal canister to see if that is the culprit but I doubt that would cause this noise. Any ideas guys?

 

Anyone have an idea? What systems or parts become active once the car is warm? It is confusing as to why it does not make the humming noise when cold, but it does when it's warm. Does anything change with the pcv system once warm? Something having to do with coolant circulating? I'm at a loss

 

tip i had from a mechanic friend about belt noise was to spray the belt with water, which helps the belt get traction, don't know might help. Problem we have here in Sweden is that it gets so cold the belts can make weird noises.

 

It makes this noise with the belt removed.

 

hang on not quite understanding this ... you took the timing belt off and started the car, which can't be because you would blow the engine up..the humming noise can come from the belt if it is not situated correctly on the pulleys or infact is the wrong belt, i.e. to small or too big, again spraying water on the belt (if I remember right a small window at the bottom of the cover if you can't be bothered to remove the cover.) helps subdue the sound for a bit. It's been more than a year since I changed my belts. Just throwing these suggestions in cause without being in front of the car it's really hard to diagnose a noise.

 

saw this on another post about humming

 

gotcha, when you said belt in your previous post I assumed you were talking about the serp belt. Of course I have not started the car with no timing belt. I was hoping to avoid taking the timing covers back off but it looks like that is where this is going.

 

Is there no hope at all of finding the noise by listening? If you can hear it, there has to be some sort of direction finding possible.


I don't think it takes 10 minutes to turn on, but one thing I thought of was the secondary air injection pump. There are sometimes emissions items on a car that only work when the engine is hot. EGR might be that way too, if your car has one.