Low oil pressure


Asked by Jan 08, 2016 at 10:29 AM

Question type: Maintenance & Repair

I have a 94 chevy blazer 5.7L 350. Just changed oil
pressure sensor/sending unit last night. Oil pressure stays
at or right around 40 for about 10 minutes then slowly
drops regardless of rpm. Will sit at 20 for a couple minutes
then starts to go under. No knocking or noise from the
motor. Don't understand. Used a mechanical Guage (my
cousin is a mechanic and has that) Guage read 60 at idle
and around 70 when revved up. Inside truck Guage reads
40 when first started, then drops.. just changed
sensor/sending unit. Don't know what else to do.. is the
Guage just off?

6 Answers


Well at least you know you have good oil pressure. I would start investigating the electrical circuit for the gauge, power and ground, It is very possible the gauge is bad.


Not trying to butt in, is the oil pressure gage analog? One wire connector at sending unit? If you take the one wire loose from sending unit, key on, ground the wire to engine block, does the gage react. I don't like to peg out analog gages. Some of these sending units provide resistance to ground, If so, you can use different resistors in the sending unit circuit, to see if gage reacts accordingly. By the way, I agree with the other person. I just thought the subject was interesting.


Hey man, we all help each other to get the best answer out there.


Found out the tester Guage I used may not work properly so I will buy a new one tomorrow to check. If the pressure ends up acting like that, any suggestions on how to fix?


My cousin (my mechanic) said if its not the Guage or the pump he's pretty much stumped


All you could do is replace the oil pump, but really wouldn't do much good if the bearing are worn. Oil pressure is developed from the bearing on the crankshaft. But you said there is no noise which is a good thing. Hopefully it is a faulty gauge on the dash. Check the oil pressure with a good gauge, see what you come up with.

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    Tom Demyan
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