I can't remember the last time I had a car with an oil pressure gauge. What is the normal pressure I should be seeing at idle? My 84 Z28 w/LG4 has the gauge maxed out at idle.

 

Wire is most likely disconnected from the sending unit. Especially if it drifts somewhat down with the key off, and goes to full-scale with the key on and engine off.

Total lack of connection = reads full-scale
Dead short to ground = reads 0

"Normal" oil pressure for that motor (before somebody comes in here with the "10 lbs per1000 RPM" crap, which is a rule of thumb for minimum required for long-term survival under racing conditions, NOT "normal") is around 15-20 idle, 30-40 cruise, hot.

 

Might just need a new oil pressure sender switch, it’s the gold bell shaped thing at the back of the engine likely near the distributor on drivers side. Mine used to read pegged out at 60psi all the time until I changed it out and now it actually reads somewhat close to actual oil pressure as verified with a mechanical gauge.

Word of caution if you do change it I went through 2 defective AC Delco replacements( both leaked oil at the crimp where the sensor comes together and proudly made in China) before finally going to a Wells/carquest that works great.

 

The 10 psi per 1000 rpm stat is really still minimum requirement however in a street engine, it still works. At idle you don't want less than 10 psi however even with hot oil, it normally shouldn't fall below 15. Since a street car rarely stays above 3000 rpm, a minimum of 30 psi is enough while cruising around but most oil pumps will put out around 40-50 psi at those rpms before the relief valve opens.

Pressure is a resistance to flow. Bearing clearances cause pressure. Too tight a bearing and pressure is increased however too tight also means not enough oil to the bearings and they'll heat up and fail. Too great a clearance and pressure drops. As long as the pump can keep up the volume this isn't an issue but if too much oil flows away from the bearings, they will fail from lack of lubrication.

Your issue however is not a bearing or pump problem. Chances are, as mentioned above, you probably have a bad sending unit. There are 2 types of sending units. For a gauge, you need one that uses a variable resistor to change the amount of resistance that goes to ground to control the gauge. The other type of sending unit is an on/off switch to turn on a warning light.

As for the factory gauge, it is far from accurate. Even after changing the sending unit, it may not show the true oil pressure. The only way to know it's accuracy is to install a mechanical gauge and compare that reading to the factory gauge.

 

There are actually quite a few types of Racing Engines that come through my Shop...
where the Crew-Chief wants no more than 5 Psi per every 1,000 RPM.

Trying to get every last HP out of an Engine.


By comparison...
My Blown Alcohol Hemi needs a steady minimum of about 120 Psi, to try and keep at least a little of the Alcohol out of the Oil.
It doesn't work so well at 75 Psi of Boost... O well.

Those 20 Quarts of Oil are only good for 1 Pass any way.

 

Mine seems to run 15 ish or above the first half white solid line at idle and the second half white line on the freeway between 30/60