Oil pressure variation, hot-vs-cold

["Mad Max"]

Now that I have gauges with numbers I now know that my 6BT has a very wide pressure difference between when it is cold and hot.



Cold, pressure at idle is ~60-65 psi



Hot, pressure at idle is ~20-25 psi.



As soon as throttle comes on pressure jumps up quick. I am actually a bit surprised at the fluxuation. The oil viscosity breaks down more than I thought it would.



I'd like to have mroe pressure at idle when hot. Maybe time to go full synthetic?



Any thoughts?



Thanks amigos,

- M2

 

[Greenleaf]

Same for me. When it cools down in October, the early AM start-up will yield about 80 psi w/15-w40 Rotella T



I often see 20 psi when the engine/oil is hot. Put the trans in drive and w/the A/C on, the oil reading on my ISSPRO mechanical is about 18 psi @ 650 rpm. It will shoot up fast when I goose her. The factory guage at this point is off the (low side) scale.

 

[cerberusiam]

The pressures are what I se also. They are normal from what I have seen of the Cummins specs.

 

[JLEONARD]

Yes those pressures seem normal. I had a good gage on my marine Cummins. When the engine was new, It would bury the 80 psi gage when cold... it actually broke the sender. The new gage could handle 150 psi and the cold pressure was about 90.

When hot at cruise (1900 rpm) it would settle at about 60 or so.

When hot at idle it was around 35-40.

That's with 15-40 Valvoline premium blue.



My Perkins would drop to 15 psi when I backed off from cruise to idle... then after about 4 or 5 minutes it would cool down enough to go back up to 25.



My Ford-Lehman does about the same... almost 75 whe cold, 50-60 at cruise when hot, then 25 at idle when hot. . creeping abck up to 30/35 after it cools a bit.



Temp has a big effect. It's normal.

 

["Mad Max"]

Eeeeexcellent That's what I was hoping to hear.

Thanks fellas.

- M2

 

[JLEONARD]

Yes it always nice when things are logical and normal.

Of course "normal" is a state of mind... and not always your own.

 

[bgilbert]

Your pressures sound fine. It's not uncommon for a newly built motor to have the same pressures at hot idle. Minimum spec is 10psi hot idle, 25psi hot cruise. On my 89 which already has a low idle rpm, when HOT, oil pressure will read about 22psi and the low oil pressure light in dash will come on. I'm thinking next time I have the dash apart, that light might just come out for good.

 

[DVolk]

Oil pressure varaition ,hot -vs-cold

my 92 does it and so does the 90

but then yet so does my small cam cummins engines as well

its a cummins thing if in doudt addsome power punch or lucas

every other oil change

 

[KPerteet]

I was having that problem with low oil pressure when the the 89 CTD warmed up, I replaced the sending unit and it showed an increase on the gauge. Last time I took it out, the pressure gauge does not move. I have the gauge/idiot light combo, and the light does not come on.

I think I am going to install a manual gauge, I think this will take care of it. Or does anyone have any idea how to fix this?