How much oil pressure is enough?

TJBaker57

Original poster
Member
Aug 16, 2015
2,897
Colorado
I finally did something I have wanted to do for quite some time. A pressure test of an LL8 oil pressure switch. Granted, this is a used part so I intend to test more samples the next trip to the yard. Even so, the results were a little surprising.

 
  • Like
Reactions: Beacon

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
That is too low for a low oil pressure warning. I thought the manual said 10 or 12 psi was the switch limit. Maybe the switch gets "loose" with age, like a stretched balloon. A new one might be higher.

Another reason to not trust idiot light switches, which is basically what this is. And another reason to put in a real gauge.
 

TJBaker57

Original poster
Member
Aug 16, 2015
2,897
Colorado
That is too low for a low oil pressure warning. I thought the manual said 10 or 12 psi was the switch limit. Maybe the switch gets "loose" with age, like a stretched balloon. A new one might be higher.

Another reason to not trust idiot light switches, which is basically what this is. And another reason to put in a real gauge.


The manual states, under the oil pressure test section, that the normal pressure should be 12 psi at 1200 rpm with 5w-30 oil but I have never seen a switch setpoint documented.

That's why I wanted to test one. Now having seen this one I want to test more of them! Next trip to the yard I will bring my meter and hand pump and check several more.
 

littleblazer

Member
Jul 6, 2014
9,265
I think the light in the vette goes on at ~10 psi. Key off it bleeds off pressure for a second or two so you can watch it creep down. Kind of fun lol
 

rchalmers3

Member
Jul 11, 2020
207
Irmo, SC
Perhaps.... your nice little pressure pump calibration is off. Do you have another way to measure pressure, for example a transducer connected to your DMM that can be Teed into the hose.

It would be good to know if your pump reading is off, so that your cooling system tests are accurate as well.

Rick
 

TJBaker57

Original poster
Member
Aug 16, 2015
2,897
Colorado
Perhaps.... your nice little pressure pump calibration is off. Do you have another way to measure pressure, for example a transducer connected to your DMM that can be Teed into the hose.

It would be good to know if your pump reading is off, so that your cooling system tests are accurate as well.

Rick
I have checked my gauge against another and they match but that could mean they are both off of course!!

For undeniable accuracy in low pressure measurements I use water column. My next experiment will be to check my gauge with a tall manometer!! 3 psi = 83.123 inches H2O. Simple test and no question about calibration unless one questions the ruler used !!
 
  • Like
Reactions: rchalmers3

TJBaker57

Original poster
Member
Aug 16, 2015
2,897
Colorado
Was at the yard in Colorado Springs all day and tested 3 more switches. One activated at 3 psi, one at 4 psi and the third was failing and intermittently activated at 3 psi. That last one had oil seeping through the switch and out the terminal end. The unexpected thing is it seemed to fail in the open state, which would mean that it reported pressure good when there was none.
 

Mektek

Member
May 2, 2017
656
FL
My electronic gauge occasionally flashes 0, but I think if that were true I would get a low pressure warning light from the switch. There's no change in engine sound when it happens.
Lousy accuracy of a fine chinese instrument I guess????
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON

Forum Statistics

Threads
23,272
Posts
637,482
Members
18,472
Latest member
MissCrutcher

Members Online