(99 XJ , Stock) Okay when I hit 4th gear or driving for about 10 mins. It sounds like a small jet engine. The sound stops when I am at red light but starts up again. Is this bad ? I just need some answers
If needed I will try to post a video

 

Have you checked your fan clutch?

 

No , but I drive an automatic or does that make a diffrence ?

 

Sorry I know how to check it know. Rookie mistake

 

Yeah the fan clutch is unrelated to transmission. If you have an HD (or a larger sized) fan clutch, it will cause more noise. Or I'm sure if it started to go bad it would make noise that it normally isn't supposed to

 

I checked the fan clutch by this method and my fan does move... but it seems like it has tension. So how much will that cost me ?

 

But the engine was kinda hot .. I left it sitting for about 4 hours. Ill check it in the morning

 

Yes, check it in the morning. It should spin easy when cold. Easier than it did when warm.

 

So if it moves easy that means its bad?

 

I'm not sure yours is bad, if it stops moving when you aren't spinning it yourself, it should be ok. do you have an aftermarket air filter on it? like one of those cone ones?

 

You may also have a bad exhaust leak. Look at your exhaust manifold and see if there are any big cracks in it.

 

Spinning the fan while warm and comparing it to its free movement when warm is a very unreliable test.

 

Your fan will still spin if the clutch is good.

I tested mine a certain way. On an older vehicle... But it wasn't safe, or recommended... Lets just say the engine was running, and it involved a long stick.

 

Well I spun it while it was cold, and it had some tension moving. So I guess it's not to bad. Ill check if I have an exhaust leak. Could it be a vacuum leak? I'll just post a video here soon

 

Consider rear wheel bearings as well.