Thoughts on Low Oil Pressure

[73inNH]

73, 351 4V Q Code, 4 Speed, factory gauge cluster in center console (including oil pressure)

My oil pressure today was really low at idle (near the "L" on the factory gauge). At 2,000 RPM it was in the lower 3rd of the safe range.

Oil level is fine. I changed it in the Spring - and maybe put 500 miles on it. I used 10W-40 dino juice.

I'm hoping this is a gauge or sending unit issue. Any thoughts about how I can test either? I'm happy to buy a new sending unit, just wouldn't mind knowing if the one in the car is indeed bad.

Thoughts? Or should I just buy a new sending unit?

 

[TommyK]

You really need to put a gauge on it to see what the actual oil pressure is before firing the parts cannon.

 

[Cleveland Crush]

73inNH, your factory "gauge" has a wide safe calibration because there is a wide range of perfectly fine oil pressure. 70psi is not "better" then 60psi and 50 is not "better" then 40psi.
As TommyK stated above, tap an accurate gauge into your oil port at the top rear block or the port just above the fuel pump mount. Let us know your actual psi reading.

 

[will e]

If you don't want to swap out the factory gauge you can add one 'under the hood'. I have a mechanical gauge. They are great. Instant readings.

 

[Don C]

You can check the resistance of the sending unit with a multi meter. Remove the connector from the sending unit, connect one lead of the multimeter to the stud on the sending unit and the other lead to a good ground on the engine block.
Set the meter to the 200 ohms position. With the engine not running the meter should read around 73 ohms. With the engine running the meter should read lower than 73 ohms, 10 ohms will mean the gauge should read maximum (be pegged). At idle the resistance will probably be around 50 to 60 ohms and decrease as the engine speed increases.

 

[73inNH]

Just realized that my cheap Harbor Freight compression tester also doubles as an oil pressure tester (I think). I'll test it out tomorrow and post results.

 

[73inNH]

Is this factory? I'm guessing, one side of this went to my oil pressure gauge, and the other side to a buzzer or idiot light?

The side that is capped was not connected to anything. The other side I unscrewed my pressure sensor from.

 

[johnnyg923]

With 10w40 i had oil pressure on the low side. I now use 20w50 and pressure is good

 

[73inNH]

Okay, so I hooked up an oil pressure gauge to the same port where the sending unit was. With the car idling (1,000 RPM, factory spec) for a half an hour I see 35 PSI. Revving it to 2000 RPMs gives 64 PSI.

I feel like those numbers are probably acceptable. I will order a new sending unit and see if that fixes the low reading.

 

[Sheriff41]

Is this factory? I'm guessing, one side of this went to my oil pressure gauge, and the other side to a buzzer or idiot light?

The side that is capped was not connected to anything. The other side I unscrewed my pressure sensor from.

Nope, not factory. Someone may have had a separate gauge hooked up there.

 

[73inNH]

Nope, not factory. Someone may have had a separate gauge hooked up there.

OK, thank you. I ordered the new sender, should be here tomorrow. I'll remove the non-factory "Y" piece and screw the sender into the block where it belongs.

 

[Cleveland Crush]

Your oil pressure is perfect 73inNH. Move on to another project with your car that needs attention