Oil gauge My oil pressure gauge jumps to high when the engine is on cold start. When my engine warms up it goes back to the middle of the gauge. When I'm driving at 2500 rpms in the first four gears the oil pressure gauges jumps back to high

When you say it was "normal" with the engine off and the key on, do you mean normal as 40-50 psi, or normal, as 0 psi since the engine was off and there should be no oil pressure? This is important because if you are reading 40-50 psi with the engine off, it is not surprising that the gauge goes "too high" once you start the engine. If the gauge is at 40-50 psi with the engine off and the key on, then there is a problem with the gauge or the sensor. It is not an overpressure issue. As long as the engine seems to be running normally otherwise and is not clacking internally or other such things that would indicate oil pressure issues, I would feel safe using the vehicle until I could have the oil pressure circuit diagnosed and repaired.

Well it could be the sending unit for the gauge.
But odds are the oil pump or engine bearings are worn out.
As the engine warms up, the metal spaces expand and the oil gets thinner. The oil pressure drops some under normal conditions, but not more than 10 or 15psi. Normal idle pressure with the engine warmed up is probably 25psi.
You could check oil pressure with a mechanical gauge to make sure its not the sending unit.
Once the oil pressure starts staying below 20psi for long periods you'll start hearing noises.

bad bearings on crank or worn oil pump. Pressure will be up when cold, but will drop when engine warms up. Check for knock in lower end. If so, bad crank bearings.

ur oil sending sensor is bad it reeds the oil pressure

Put manual gauge to make sure if cold and hot oil pressure. If pressure low when engine warmed up may be oil pump or engine bearing problems.

Look for the oil pressure sending unit on the block or the cylinder head on the V-6 or V-8 models. --- OIL PRESSURE TEST Check for proper oil pressure at the sending unit passage with an externally mounted mechanical oil pressure gauge (as opposed to relying on a factory installed dash-mounted gauge). A tachometer may also be needed, as some specifications may require running the engine at a specific rpm.

1. With the engine cold, locate and remove the oil pressure sending unit.
2. Following the manufacturer's instructions, connect a mechanical oil pressure gauge and, if necessary, a tachometer to the engine.
3. Start the engine and allow it to idle.
4. Check the oil pressure reading when cold and record the number. You may need to run the engine at a specified rpm, so check the specifications.
5. Run the engine until normal operating temperature is reached (upper radiator hose will feel warm).
6. Check the oil pressure reading again with the engine hot and record the number. Turn the engine OFF.
7. Compare your hot oil pressure reading to specification. If the reading is low, check the cold pressure reading against the chart. If the cold pressure is well above the specification, and the hot reading was lower than the specification, you may have the wrong viscosity oil in the engine. Change the oil, making sure to use the proper grade and quantity, then repeat the test. Low oil pressure readings could be attributed to internal component wear, pump related problems, a low oil level, or oil viscosity that is too low. High oil pressure readings could be caused by an overfilled crankcase, too high of an oil viscosity or a faulty pressure relief valve.
   

Two things...when it reads zero, is there any engine noise (tapping or knocking)? After you rev the engine does the pressure read normal at idle and function normally, or does it go back down? Either way, you should not drive the vehicle 'till you have a mechanical gauge (yours is electro-mechanical) put on there and the actual pressure is tested. The condition may be a bad sending unit, a bad bearing or possible obstructed oil pump screen. The repair is obviously different for each one and the price is as well.

This may not be your fix, but a place to start is having a technician check your EGR operation. (Exhaust Gas Recirculation Valve). The EGR helps the car reduce emissions by letting exhaust flow back into the intake to burn up unburned gas vapor while warming up your car. (When your engine is cold, it will not always burn up all of the gas that goes into the cylinders, so that gas just goes into the atmostsphere). When the engine warms up, it is unneccessary for the EGR to still be open. If it remains open, it can make your engine die, beacuse there is more exhast than air and fuel being burned. The reson this would happen would be if the EGR Valve stuck open (frequent issue).

Hello mb4494: My name is Roger and I will help you. If by changing the oil pressure sending unit the problem did not change. I would perform a oil pressure test. This is done by removing the oil pressure sensor and inserting a oil pressure gauge. This can be done by yourself or by a repair shop. This needs to be done on a cold engine. Start the engine and observe the oil pressure cold.as the engine warms up observe the pressure. The pressure will drop off as the engine warms up.Should the oil pressure drop below 10 to 12 PSI. then you have internal engine trouble. More then likely a bearing problem. Try dropping the truck into gear and see what the pressure drops off to. Again if the pressure drops below 10 to 12 PSI. you have a problem. I would also check to make sure you have the correct oil switch. a truck with a oil light uses a oil pressure switch. with a gauge you would use a oil pressure sending unit. Sorry for the long reply but want to make sure you check the pressure correctly. Please rate the quality of the answer as this is how we know the answer was correct. Thank You for using Fix Ya. Roger

You need to have a mechanical test gauge hooked up to see if this is a false reading, this special gauge goes into the oil sender tap in the block and will let u know for sure if the pressure is to high cold, if it is the most common issues are wrong weight of oil, do u use oil heavier than 10W-30W? any other oil like 10W-40W will cause high oil pressure readings, the reason is the very tight rod and main bearing clearance's the engines now use, it is only about 1/2 the clearance of older engines, that is so the new fuel saving thin oils can be used.