RPM stand for Revolutions per Minute and relates to the frequency in which the crankshaft is turning inside of the engine. The crankshaft turns as long as the engine is running and when the engines runs faster the RPM will also increase. As the car increases speed to change gears the engine will increase RPM until it is ready for the next gear. Just like on your bicycle when you shift up or down your leg rotation speed changes in direct proportion to how hard it is to pedal.
When the oil is cold the pump has lots of preasure . When it warms it drops at idle but depends on the rpm of the engine. It sounds like it is operating correctly other than the preasure may be showing a little high. If you want to know the correct preasure have a manual gauge installed.
Rpm stands for revolutions per minute. This is talking about the revolutions the crankshaft goes per minute. The faster you go to more revoultions that are accomplished. Therefore the faster you go, the rpm goes up. And as you slow down it goes down.
Could be low on coolant or a faulty thermostat.
The spark plug gap can cause the RPMs to fluctuate, while idling. The more probable cause of the fluctuating RPMs is a bad camshaft.
different trim levels and options as ordered when the truck was new. If you really want or need a tachometer, you can go to any auto parts store and buy an aftermarket one. they are pretty simple to install too.
The water evaporated.
do you mean warmed up ,at idle, the rpm surges up and down with out foot on gas ?
The oil pump is driven by the engine. Turning the engine faster means that the oil pump spins faster, this creates more oil pressure. 80 psi is normal at high rpms, and will not cause any problems.
bad sending unit
the Air conditioning would have to work harder - its a guess depends if the gauge is showing Battery Life or Battery Output
You hold the y down and the gauge will go up
The amperage gauge will go down when you turn on your lights, because there is a sudden draw of electric power from the battery. The alternator should equal out the power surge.