Oil pressure drop with bypass - what's acceptable?

[JohnStra]

Truck is an 03 Dodge Ram Cummins. Bypass is a Gulfcoast O-1.

I have a mechanical oil pressure gauge on a "T" at the port I'm drawing oil pressure from (oil filter housing).

I get quite a drop at cold idle (from 65 psi to ~50 psi) with the bypass running wide open. I have an inline needle valve on the input side and I can choke down the flow so the pressure returns to almost normal. With the flow choked down this way the filter still gets good and hot at operating temp so I know I'm getting flow through the filter. I have not attempted to measure the flow rate yet.

How big a concern is this pressure drop? Is the needle valve an acceptable solution? How far can I choke down the bypass flow and still get good filtration?

Thanks,
-john

 

[Gary Allan]

If I grasp what you're describing correctly...

Needle valve 100% closed ..65 psi
Needle valve 100% open ....50 psi

Where is your dash indicator pressure taken from, and how is it altered by changing the needle valve?

As a loose standard of practice, I'd choke back the needle valve to some point near or at the normal pressure. Since it still gets warm, you're still filtering.

I'm surprised that this can pass that much cold oil to drop that kind of pressure at the source. Cold I would expect it to be a virtual dead end.

 

[JohnStra]

Yes, you have it right.

Good question. Dash oil pressure comes from a sensor on the other side of the block, and it does not reflect the pressure drop I see on my gauge. I'm inclined to believe my mechanical gauge is more accurate since the dash gauge on my truck is computer controlled - it's not really an analog gauge.

Thanks,
-john

 

[unDummy]

Your gauge sender is too close the the 'leak' and pressure drop from the filter. Sender location further downstream would be better.

Since GulfCoast uses a pretty big orifice(.078 but don't quote me), it might be better to just reduce the orifice to .0625-.040 and not even worry about it.

If you don't want to change the orifice, pinch it for a 10psi pressure drop. 15psi seems a little extreme but your engine is overbuilt and should have no problem even with the big orifice. Read the directions for the 0-2. Gulfcoast wants to be contacted if there is a 10psi or more drop(hint time for smaller orifice).

Or ignore the PSI and just measure the output flow. You'll get good filtration with adequate flow. Too much flow might force soot through the filter. 1-2 quarts per minute when hot at idle is a got starting point. Reduce pressure loss until flow is <2 quarts per minute.

 

[Gary Allan]

I'm not reading you correctly, undummy. I think that you're saying that he's dropping enough over the lines to see a decent pressure drop from the port to the filter ..but I see him saying that if he unthrottles the metering valve ..he's losing pressure at the port .which isn't the same thing. He's overloading(draining) the supply without a restrictor. His drop across the filter is whatever the pressure supply is vs. zero. In this case, PSIG is PSID.

I basically agree with everything else you say ..but I can't reason that part of it.