The Xterra is fine now after a visit to the garage. A water pipe leading to the oil filter to cool the engine oil developed a leak. I was surprised the engine oil going in and coming out of the oil filter has a water circulation line to cool it. The torture it gave while coming home after the drive was too much. Every 15 min I had to stop and fill the radiator with water while engine was running. Combined with the hot weather and the hot engine with hot radiator made me dead tired. Regarding the air pressure I had deflated to 12 psi all the tires at the beginning of the drive. No idea how it went up to 17 psi on 2 tires. After @marks helped me to deflate the tire to again 12psi after half an hour the pressure rose up to 15psi. Probably had to do with the climate and the fact that those tires have done almost 40000kms. Maybe its time to change all the tires in a months time.