Oil light
Seasoned HDF Member
Joined: Sep 2008
Posts: 14,076
Likes: 11,096
From: San Diego, CA
OP, more info would certainly be helpful...
However, I don't believe the oil light measures oil pump volume. I believe it measures oil pump pressure. Pressure and volume are different measurements. The idiot lights tend to be more accurate than the HD OEM gauges. And an idiot light indicating zero oil pressure, may also be an indication of no oil flow.
The bearings in an HD motor need flow, not pressure. So in the past, a sporadic low pressure condition at idle was not always an alarming condition.
However, if you are losing all oil pressure at idle consistently, and it's a new condition, I would investigate.
On a fresh top end rebuild, with the idle pressure lower than before the rebuild, I'd be curious as to why...
I'd start by putting a good pressure gauge on the engine (not an OEM HD gauge) to see what the pressures actually are. If no oil pressure was consistently measured at idle, I would suspect I made a mistake during reassembly of the top end rebuild.
Last edited by hattitude; Aug 7, 2025 at 08:22 PM.
Road Master
Joined: Nov 2018
Posts: 920
Likes: 896
From: Upstate NY
As oil heats up, it looses viscosity. Imagine maple syrup just out of the freezer versus a bottle thats been sitting on the counter all day. You aren't losing volume, you are losing pressure. (yeah yeah, I fully understand how the 10W30 etc labeling works) Id assume you need to run a thicker oil.
Try the simple shet first.
For a while I was into older cars, all the new oils seemed to loose pressure when they got hot, I just started running straight 30 (SAE30) and it alleviated the problem.
Try the simple shet first.
For a while I was into older cars, all the new oils seemed to loose pressure when they got hot, I just started running straight 30 (SAE30) and it alleviated the problem.
Stellar HDF Member
Joined: Sep 2017
Posts: 2,132
Likes: 570
From: memphis
yep...specifically that oil pump oring install.
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