I came into possession of an 06 Frontier. The previous owner told me it kept overheating and probably had a bad head gasket. I took out the thermostat and checked it, filled the vehicle with fluid and tried to make sure there were no air blockages by removing the rubber cap on the exit hose of the heater core. Started the motor and it ran smooth. Took it for a 9 mile ride and the temp gauge never went past mid point. Just as I pulled into my driveway the motor dropped oil pressure and quit. It would restart for a few seconds and then shut off. I left it sit over night, check the fluid level and put about a quart in the radiator. Did a compression test on the three cylinders on the driver side 145 psi, 150 psi and 155 psi. So I took it for a ride. I made it 11 miles and it did the same thing to me. Oil pressure dropped to nothing and the motor shut off. Would start but instantly stop. Might be a coincidence but both times it did it I had just pulled a hill. All the while the temperature gauge never went past halfway. The motor didn't smell hot but when I removed the recovery tank cap (with a rag and rubber glove) water spewed out of it. When i turn it over with the radiator cap off water belches out of the inlet. My next move is to pull the intake manifold and do a compression test on the three cylinders on the passenger side. I'm a bit lost. Normally I would test the gauge by grounding the wire to the sending unit but I haven't found the sending unit yet. Anybody have any ideas?