I've changed the oil on my 03 4runner many times, and never had a problem. This time, the cap from the drain under the oil filter mount came off, and oil spilled on the belt and top of the ac compressor pulley. Now when I start and run it, there is a loud squeal that gets louder when I accelerate and nearly goes away when I slow it down. When the ac clutch kicks in, it squeals a bit more. Will this go away in time?

 

Maybe... but it will go away a lot quicker if you clean the pulleys and replace the belt.

 

NO!! This will not go away until you use soapy water and wash the oil off then you can use a drop or two on the belt to make it sticky and no more squeak!!

they do make belt dressing compounds but the old school is to soap.
When dish soap gets spread out and drys up it becomes sticky and stops squeeling belts