Oil pressure

Although I once owned a '48 Dodge that would show a drop in Oil Pressure at idle, for the most part, every car (or plane, for that matter) with an analogue gauge, shows a steady oil pressure regardless of engine rpm. However, I once owned a '99 Olds Aurora with a digital oil pressure gage. It would show varying OP from about 20 psi at idle to between 60 and 70 at highway speeds.

Is this phenomenon because of better measurement (analogue vs. digital) or was my Olds just different.

Every car I’ve ever had always shows different readings at different RPM’s regardless of whether the guage was analog or digital. The only time not was when I got the wrong sending unit for a light instead of a gauge and then it had a steady reading. I can’t imagine that a plane would not show an accurate oil pressure unless designed to supply a constant pressure.

Some gauges are simply idiot lights in disguise. Ford being the biggest culprit. Basically they are set up so that as long as there is a minimum amount of oil pressure the needle will go to somewhere in the “normal” band regardless of actual oil pressure. If there is no oil pressure the gauge reads zero. Of course if this happens whilst driving, the damaage has already been done.

I also owned a 1948 Dodge and the oil pressure would drop at idle. The oil pressure gauge on the 1948 Dodge, as I remember, was mechanical. Modern cars have an electronic gauge that uses an oil pressure sending unit. As I remember, the cars I had with the non-electronic gauges did show reduced pressure at idle. These included a 1947 Pontiac, 1948 Dodge, 1954 Buick, 1955 Pontiac and a 1950 Chevrolet pick-up truck. I reasoned when the engine turns slower at idle, the pump doesn’t turn as fast and hence less pressure. The vehicles that I have had since the ones mentioned above either had warning lights or digital gauges.

Some cars have a gauge that is really nothing more than a light. It is good or bad. Some oil systems have a relief valve to keep it at a design pressure. Others have neither.