Is 21 psi oil pressure @ idle too low?

[Brian R]

Now that I've got my mechanical gage installed I have to grapple with the numbers. The gage was showing 21 psi at idle in drive with my foot on the brake and the AC on yesterday, a mid 80's California day. Does that sound too low? I remember my Ford 7. 3 used to idle at around 15 psi. My Dodge was idling a bit slowly so I bumped the idle speed up and I'll see what numbers I get on the way home today. Anybody have any numbers from their mechanical gage?

 

[paccool]

Brian, I can look tonight when I get home to see what the Cummins book says about "normal" pressures. Someone will probably have answered by then so I'll check this post first.



Stan

 

[MDKram]

Typical rule of thumb is 10 psi of oil pressure (minimum) for every 1000 RPM. i. e. don't worry if you only have 20 psi at idle.



Regards,



Marc

 

[Brian R]

Thanks for the comforting replies. It would be nice for peace of mind, though, to hear the factory spec.

 

[paccool]

OK Brian, this may make you feel a little better! I have a Cummins Operation and maintenance manual for B series engines. For a 160 HP B5. 9 used for automotive use:



Minimum allowable pressure at idle = 10 PSI

Minimum allowable pressure at rated RPM = 30PSI

Regulated pressure = 65 PSI



"Regulated pressure" is the pressure the bypass spring opens up and puts oil back into the crankcase. This should be the highest pressure you see on a gauge.



I would be worried if I only had 10 PSI at idle, 21 PSI doesn't sound too bad. What is your maximum reading when crusing down the freeway?



BTW, the manual was printed in 93 but the engines are the same basic engine from 89 to 93. Shows 5 different HP engines from the 160 HP the way up to 230 HP and the oil pressures are all the same.



Hope this relieves the tension a little!Oo.

 

[Shrimpy]

Hey Brian I wouldn't worry. Like Stan showed, the minimum is 30 psi at RPM. Just as some reassurance, when I had my First Gen. with 200,000+ miles on it towing 6500 lbs in 100 degree Texas weather with 95% humidity, It would be about 42 to 46 psi at RPM and stopping with the a/c on in gear would drop to 19 to 21 psi. I think you are fine like Stan said. Good luck.



P. S. Sorry for the run on sentence





P. S. S. You are smart to go with a Mechanical gauge. That was one of the first Mods. I did. Mechanical water temp. and Oil pressure.

 

[paccool]

I forgot to say one other thing. The book says there is a 20 PSI differential across the oil filter so I guess this means the max pressure would be about 45# at the gauge since the sending unit is mounted down on the opposite side of the block. Brian, let us know what you get for max, Shrimpy is right there if I'm correct.



I have the factory gauge and it runs right at midpoint at RPM and doesn't drop much at idle. Guess I need to consider a mech one just for safety.



Stan

 

[R.E. Miller]

Good news!!

I had installed a mechanical gauge, and thought that the pressure was too high at RPM... 42-57 psi.

Thanks for the good info, and mine does idle at 25 psi FWIW.



Russell

 

[Bugman]

I have found that the range of oil pressure reading changes with different sending units.

 

[Brian R]

Mine cruises at about 59 psi down the freeway (mid 80's ambient temp. ). Thanks for all the replies. I guess I won't worry unless idle gets down close to 10. We'll see how the Sacramenot heat effects things in a couple of months.