There is not contamination in the oil, so luckly is not a blown head gasket,
Probably is the cap that is not holding the pressure as you said, But I am not sure if other thing can cause it, Not excesive fuel consupmtion, just like 25 MPG in the city with 93 octanes,
I also noticed that the temperature moves a lot from N-O to M , is it normal?? (is oscilates)
but never over M (here is a little hot 35-40C, 95-107F the most of the time)
i am new with this car, does it have just one radiator cap (the reservoir one) or has two as other cars? (one in the radiator and one in the reservoir)
Any other clue??
