What causes drop in oil pressure reading after warm up?

check engine connecting bearing

The most common cause is worn engine parts. As the oil warms up it gets thinner and internal leaks cause the pressure to drop.

You need to pull the pressure sensor and install a manual test gage, (borrow from Autozone or other chain part store) that is the only way to verify the engine is not loosing oil pressure.

How many miles are on the engine? Have you tried to replace the oil pressure switch? is the engine making any type of noise due to low pressure reading?

The first thing to determine is whether the oil pressure sending unit is bad or the engine actually has low oil pressure. To determine that you can remove the sending unit and adapt a mechanical oil pressure gauge in the hole. You should have a minimum of 20 lbs. pressure at idle and 40 lbs. above 1,000 rpm on a warm engine. If the pressure readings are good, replace the sending unit; if not, you have an internal engine problem.

Connect test leads to the guage and apply 12 volts, if the guage activates upward this works, if it's the oil preaaure in regards to the oil pump, you need to hook up a oil pressure guage.

Install an external mechanical (yours is electro-mechanical) oil pressure gauge on the engine and read actual oil pressure. If it is below 15psi at normal idle warm, (I like a reading of 30 or above on jeeps) then you will need to determine the reason. Causes can range from worn bearings to obstructed oil pump pickup screen. Any knocking inside the engine tells you there is a bearing problem...really doesn't matter which bearing it is, likely all are worn and will need replacement, or engine needs rebuild or replacement. I've been doing this a long time and have found that in-car bearing replacement, unless done very early on and "matching" bearings to existing clearances, will most times relieve the problem for a few days or weeks and therefore is pretty much a waste of time and $.
If mechanical gauge reads normally, likely the sending unit or the passage going to it is plugged or the unit itself is going bad.

Check oil level.
First verify the pressure is dropping and not some other problem.
You will need to connect a pressure gauge to the engine to read the true pressure.
If the pressure reads good then the sending unit is bad.
You should have new oil and filter. A bad filter can cause pressure drop.

Is it possible that you are using a different brand or weight of oil? 10w30 instead of 10w40 could potentially cause this.


Can also be caused by engine running warmer for some reason.

3 psi shouldn't be much of a concern.

You can try a heavier weight oil if you want it to be a little higher.

how low does the oil pressure drop?? is it below 40?