My wife's 2010 Volvo s40 t5 r design antifreeze sounds like it's boiling and she gets a loud whining/screech from time to time after the car gets up to temp. The temp gauge shows it's at perfect temp though. My first thought is water pump or thermostat, (Im not a huge mechanic but know enough to replace parts.) But I'm wondering if there's anything else I should be checking? Thanks in advance!

 

This noise is normaly the PCV system , when it starts to make the noise pull the dipstick out , if it stops then that is your problem
However that will not cause the coolant to boil , but the coolant circulates so may look like boiling as it flows

 

Might have to dumb it down a little for me I'm sorry. Which dipstick should I pull and if that IS what's causing it what should I look to replace?

 

The oil dipstick. Or you can open the oil fill cap. If that stops the noise the problem is in the PCV system, and the noise you're hearing is air being sucked through engine seals (which can sound an awful lot like a bad bearing).

 

I was able to take that cap off the pcv and sure enough the seal was broken

 

Great its not easy to take the cap off while the PCV is in place and therefore quite easy to damage the cap , I removed mine to replace the faulty diaphragm