On this page we will discuss how to perform oil pressure testing and what can cause lower than expected results. But first lets talk about why we should bother with testing it at all. The big reason is that it's a strong indication of your engines overall internal health.
Just as blood
pressure can be used to determine the health of a human being. The
oil pressure test is used to determine the wear of an engine's internal
parts. The testing procedure is performed with mechanical gauges
measuring pressure of the oil as it circulates through the engine in real time. Factory gauges might not be accurate or tell the whole story.
Why is low pressure bad? Basically the pressure of the oil depends on the efficiency of the oil pump along with the clearances through which the oil will flow. Excessive clearance is most often caused by worn bearings and will cause a decrease in oil pressure. Some common worn bearings would be the crankshaft main bearings or the connecting rod bearings. In some cases I've seen worn camshaft bearings cause low readings.
A loss of engine performance, flickering pressure warning light on the dash, excessive engine noise, and even poor starting can be caused by abnormal oil pressure. When the engines oil pressure is too low premature wear of its internally lubricated parts can be one of the results.
the above listed problems mentioned will cause me to break out my
mechanical gauges and get a reliable reading. Personally
I do not trust the oil pressure gauge on the dash. This is because
there is a lot of room for error between the electronic sending unit and
the gauge itself.I will say however that the newer the car the more reliable the electronic readings seem to be. If you have an 84 Fiero I would hook up a mechanical pressure tester.
The easiest way in my opinion, to be sure you will get an accurate mechanical reading from the tester is to remove the factory installed sensor. If a vehicle has an idiot light or gauge it will have an oil pressure sending unit somewhere on the block or cast area.
You will want to make sure that you follow the instructions provided with the fluid pressure tester. The tester I own on the left does both transmission and engine oil. Take my advice and use Teflon tape or compound on the connection fittings. Remember if you do not have a good connection you may have a large mess to clean up.
You should also look up the specifications for your engines pressure in a car repair manual. Also note that the pressure is read when the engine is at normal operating temperature and results are recorded at idle speed, and usually around 2000 RPMs. Excessive bearing clearances are'nt the only causes of low results.
Sometimes they can be pump related problems. An example would be a restricted pump pickup screen. This can be commonly blocked by sludge from lack of maintenance. Also note that a week or broken pressure relief valve, low oil level, contaminated oil, or even a low viscosity oil (wrong weight) can all cause low-pressure readings.
On this page we discussed the how and why of testing internal engine
wear. I have a lot more information about other tests you can use to
check the health and well being of your engine. Learn the theory and operation as well as advanced testing procedures on my page that provides details about
automotive engine repair and testing.
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