Why This Happens?

[b4summer]

Hi, I don't know much about mechanical stuff, and I know most of you guys are mechanical guru, so I hope someone could help me with this problem I'm having with my R33.

I have a complete stock R33 GTS25t manual series II. About sometime after I had my car service done with 10w-60 engine oil, it now makes louder noise from the engine bay and makes less power than it used to before the service.

The car used to be quite when the engine is on, I've been using other engine oil (not 10w-60) from the mechanic shop and it runs very well.

After 1 or 2 weeks after I start using 10w-60 (maybe the new engine oil isn't the thing causes the problem), things changed, it's got less power and it makes much louder noise.

So I wonder why this happened?

I'm thinking maybe the mechanic filled in too much engine oil because I can see from the engine oil stick (I'm not sure if that's the right way to call it), but the mechanic told me they used around 5 liter so that's the right amount. And I also think maybe the belt needs to be changed as it's done almost 90k (it's unreal I know but the car is like brand new inside and out).

Does anyone know why?

Thanks in advance.

Edited August 31, 2009 by b4summer

[BoyWhoCriedWolf]

This sound that it makes, can you describe it for us?