How low is Low Oil Pressure?

[MojaveJoe]

Drove to town last night (about 30 miles). Once there I noticed my OEM oil pressure gauge would drop to minimal operating range when ever the engine was at idle speed (750rpm).
Raise the speed to 1250rpm and it would be back to mid range oil pressure. (see pics below) Ive never saw such low oil pressure on my original 5.9 305HO truck. But this 5.9 325 truck's oil pressure has me worried. Am I looking at a warn oil pump, dirty oil syndrome or what? Just need your input RE: if Im driving on borrowed time when hot oil pressure goes so low at idle.

Check oil level this cold AM and it was about 1/2qt above full. Started cold engine and ran for 5 minutes. Shut down, waited 5 minutes then checked oil level again. 1/4 qt below full mark then.

When starting cold engine this AM oil pressure ramped up to mid range at idle right away. Slightly over mid range at 1250rpm.

All advice and experiences welcome.

 

[RustyJC]

You might want to check THIS THREAD.

Rusty

 

[MojaveJoe]

Thanks, Rusty
Seems normal from the thread link. Hmmm. Where can I tap into the engine to install a mechanical oil pressure gauge? If the computer is lying to me, seems my idiot gauge pressure w/ cold oil would run the same as hot?

 

[RustyJC]

Not sure about the 3rd generation 5.9L, but the oil pressure gauge display algorithm probably takes engine temperature into account. My 6.7 EVIC displays 49 PSIG consistently at 65 MPH (~1725 RPM) hot and 23 PSIG (IIRC) at hot idle, but I'm told that there's no actual oil pressure sending unit on the 6.7L Cummins, just a 5 PSIG switch, so the EVIC displayed value must be calculated from a computer algorithm just like the oil pressure gauge display.

I think there was a mention on the thread I linked of a pipe plug at the oil filter head where you could tap into the oiling circuit for a mechanical gauge reading.

Rusty

 

[p-Bar]

It's a "make you feel good gauge". When in doubt put a mechanical one in for testing

 

[BarryG]

unsure about the third gens but on 2nd gens there is an auxillary port on top of the oil filter head as Rusty mentioned be worth checking

 

[Bob4x4]

Yes the 3rd gen has an 1/8 npt port on top of the filter head some have 2 ports

 

[DaveHess]

I pulled the plug that is directly above the ECM on the driver's side of the block. I hooked up a braided line to a mechanical guage. During hot weather or after the engine reaches operating temperature, I will see oil pressure as low as 12 PSI at idle. Cold starts a little over 60 PSI and running down the Interstate anywhere from 45 to 55 depending on RPM. The reason I used the port on the side of the block is I use the port on top the oil filter head for oil temperature. In comparison at hot idle, the factory guage on the dash will show about 40 PSI at idle a little over mid scale running at speed. The plug on the side of block is not real difficult to get to or remove. I pulled the driver's side fender liner and just lowered it down on top of the tire. You then have excellent access to the plug. The plug is metric and apologize at this time, the size escapes me. I removed and replaced it with a fitting to adapt pipe threads to the braided line. Again I apologize that I don't know the correct terminologies. I just just figured it out as I went. I did use teflon tape on the fitting going into the block and there has been no leakage. One other thing I did note after the installation of the mechanical guage, the amount of time it takes to get oil pressure. We're talking 1 to possibly 2 seconds on a cold start. I also use an Autometer Phantom oil pressure gauge. I like the white face and bright orange needle for quick glances at the gauge. I hope this helps you!

 

[DaveHess]

I need to make a correction to my post. At idle the factory gauge does not go below the left hand heavy mark. I stated it to be 40 which is mid-scale for me, Sorry about that.

 

[AH64ID]

Mojave, if you are seeing that much fluctuation on the OEM idiot gauge you have an older software version. The newer the software the less the idiot gauge moves. You may gain other benefits from having the software updated. Anyone you know with a Smarty can do it for you.

I pulled the plug that is directly above the ECM on the driver's side of the block. I hooked up a braided line to a mechanical guage. During hot weather or after the engine reaches operating temperature, I will see oil pressure as low as 12 PSI at idle. Cold starts a little over 60 PSI and running down the Interstate anywhere from 45 to 55 depending on RPM.

I am taking oil pressure from the same port, but you run a bit lower pressure than I do. I have ran 2 different oil pumps and 2 different brand gauges and don't generally see that low of pressure on normal driving. I would guess your gauge reads a little low.

Warm Idle is 18-20, HOT idle (just got done towing on a HOT day) will occasionally light my 15 psi warning light but generally 16-18.
Cold start will go as high as 85 psi but quickly drops to around 70-75 max, at 1800-2200 rpms.
Cruise is ±60 but will drop as low as 45-50 when pulling big grades in the summer on a HOT day.

 

[DaveHess]

Thank you John. After seeing your post it came back to me you were the one who helped me in this install and I thank you again for the information. I must confess the numbers I provided above were from memory. My Ram gets about 4,000 miles a year on it. It hasn't been out of it's garage bay in probably close to 60 days now. So, I apologize if the numbers are not 100% correct. To be honest, I watch it closely on starts to be sure I have pressure before moving and I will glance while operating. I get the warm fuzzy knowing I am actually reading oil pressure not watching a moving idiot light.

 

[AH64ID]

Thank you John. After seeing your post it came back to me you were the one who helped me in this install and I thank you again for the information. I must confess the numbers I provided above were from memory. My Ram gets about 4,000 miles a year on it. It hasn't been out of it's garage bay in probably close to 60 days now. So, I apologize if the numbers are not 100% correct. To be honest, I watch it closely on starts to be sure I have pressure before moving and I will glance while operating. I get the warm fuzzy knowing I am actually reading oil pressure not watching a moving idiot light.

It is awfully nice knowing there really is pressure, isn't it!!!

Mine only got about 8K on it this year, if that, and 1200 was thanksgiving weekend so I know what you mean.