I found the usual engine roar is different and I check everything. Only thing I can find is this floating stuff on coolant(water). Please see the attached pictures. I'm not sure whether those are dirt on water or the oil?
Sounds like head gasket broken. Is my assumption correct?

 

Sure looks like oil is getting into the coolant to me. Could be the oil cooler thats mounted on the oil pan also which would be a easy fix-I would look at this first

 

Thanks for the reply, I washed the radiator reservoir and by passed the oil cooler. And it seems the mixing happens inside the oil cooler.

Now I'm looking for an oil cooler. Now I'm middle of two options. Non-branded oil cooler($40-60) vs BEHR($200-250) oil cooler.

 

Where would the oil cooler be located?

 

Its attached to the bottom of engine, below crank pulley, near oil filter, the electric transformer like aluminum box which have two horse connections. see the picture.

In my case it was the oil cooler. I replaced it by myself, and flushed and clean the coolant. Everything is great and running fine now.

 

Thanks for the info. I think I may have a blown head gasket. I was hoping it could be something as easy as fix as you described.