A big fat phony

Little known fact that most people would never guess: The oil pressure gauge in 94-96 civilian Caprices and Impala SSs is a fake.  It's nothing more than a fancy idiot light.  If there is more than 5psi of oil pressure, the needle moves up to a set point and does not change.  In all likelihood, GM did this to alleviate warranty claims.  The gauge it's self is perfectly real, but it's hooked up to a simple on-off pressure switch and fed through a resistor to make it read about 3/4.  Only the police Caprices got actual pressure senders, and gauges that move.

Because the gauge is real, and all the wiring is there, it's easy to make it work.  There are two options for actual pressure senders.  The first, and most obvious choice, is the factory police sender.  It's a direct swap for the original Impala sender, however it tends to be expensive, and is calibrated for 80 PSI.  Because it's an 80 psi sender, it will make the gauge read low.  A better choice is the Chevy pickup truck sender.  It is rated for 60 PSI so the gauge reads in a more "normal" range.  I'm using Napa # MPE OP6869SB, listed for a '90 Chevy 1500 pickup(though they used it for a wide range of years).  

The downside to the truck sender is that it uses bigger threads than the original sender, so you will need an adapter.  The adapter you need is 1/8" male pipe to 1/4" female pipe(picture shamelessly stolen from the internet):

Installation is as easy as unscrewing the original sender and screwing the new one in.  It's a tight fit since the sender is on the block behind the intake manifold, but it's reachable.  There is one other problem though, the resistor.  If we don't take the resistor out of the circuit, the gauge will read far, far to low.  Unlike the sender, the resistor takes some digging to get to.  It's wired in line with the gauge wire in the harness bundle stuffed above the glove box.  Since I had my whole dash out, it was right there, but if your dash is assembled it can be tough to reach.  In addition, GM seems to have found the stickiest tape in existence for their wiring harnesses.  Despite being nearly 20 years old, it's still as sticky and gooey as ever.  You can see where the resistor is in this pic.  It's the thing with the big red arrow pointing to it:

All you need to do is snip out the resistor, being sure to leave the tan wires connected to each other(these are the wires that go to the gauge).  Tape off the bare end of the tan wires, leave the black wire disconnected but tape it off too.  With the resistor gone, and new sender installed, the gauge actually works.  On my 166K mile car running Mobil 1 0W-40, the gauge reads around 5/8 cold, 3/8 hot.