Jaguar Repair: oil pressure, hydraulic gauge, oil pressure sending unit

Question
I have replaced both the oil pressure switches.  The car IS getting oil.  There is never a noise in the engine.  However the pressure reads between 0 and a little above 20(sometimes).  Do I need a new gauge?

Answer
Hi Pam,

That low of a reading can be serious or not. Even though you have not told me what kind of car this is, it doesn't matter as most all are about the same in this area.

First step is to find out if it is a gauge problem. The way to determine if the gauge is the problem is to connect a known good hydraulic gauge to the engine. If you don't have a shop near by that can run the test, most auto parts stores have accessory hydraulic gauges that are not expensive. They usually come with an assortment of fittings so you should be able to adapt it to your car in place of the oil pressure sending unit (if the gauge on the car is electrical)

After you confirm the true oil pressure you can take steps to correct the problem.

Oil pressure it built up as the oil pump tries to force oil through the bearings and since the oil pump has a very high capacity to pump a high volume of oil and all of it can't get through the bearing clearance, pressure builds up. The pressure will build to an extreme until something broke so a pressure regulator valve is designed into the system to bleed off the excess pressure.
This regulator is placed in different places on different cars. Many domestic cars have it in the oil pump itself. Most older Jaguars have it in the filter block and many other British cars have it in the engine block.

There are many possible causes for low oil pressure. The most common is a faulty pressure regulator valve and faulty electrical gauges. Other problems are worn bearings preventing much pressure build up and several other causes particular to each design engine.

The fact that you have not heard any engine noise is a good sign but you still need to test the pressure with a know good hydraulic gauge first. Then if the actual pressure is good go after the gauge, power supply or sending unit if it is an electrical gauge.

Howard