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91 Dynasty 3.3 engine. The oil pressure gauge on the dash does not work most of the time. The needle just stays pointing down, but occasionally it will make an effort to creep up. Sometimes it looks like it wants to move up halfway and other times it looks like it actually works, but it is maddeningly unreliable.

The question is, should I care? The only reason I might care is because I don't understand oil pressure or how the oil pump even works. I've just been assuming that the oil pump and the oil pressure is correct and only the gauge is malfunctioning because the engine runs very well.

Am I playing with fire by ignoring the gauge issue? Thanks for any advice.
 

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The sender could be leaky... pretty common issue. The Imperial's original one would sometimes read no oil pressure at all until the engine was running a couple minutes. Oil changes usually made it better for a while, but it always went back to its old behavior. It also read rather low sometimes as well... not low enough to turn on the check gauges light, but it always irritated me.

Swapped the sender out for a new one, and the gauge has been reading healthy ever since. The only times it reads no pressure now is if the car hasn't run for days, and those times it always comes up into the healthy zone within seconds.
 

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Does the red 'Ck Gauges' or 'Oil can symbol' light come on when you turn the key on but don't start the car? They may offer some warning if a failed oil pressure situation happened.
 

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The oil pump is usually a gerotor type pump (picture a plus sign being rotated inside a five-point star, every time the plus sign touches the inside of a lobe of the star, the cavity between it and the star decreases in size, creating pressure) driven off of some major engine component. I don't know how they're driven on the 3.3/3.8, but the 2.2/2.5 drive them off of the timing belt. The oil gets forced by the pump through holes drilled in the block and head (oil galleries) to critical components like the valvetrain, camshaft, crankshaft bearings, piston rods, etc., before draining back to the crankcase to be sucked up again by the pump. The oil also supplies the hydraulic lifters, which are essentially little hydraulic cylinders that close the gap between the camshaft and pushrod (or rocker arm, in the case of the 2.2/2.5) to keep the valvetrain from rattling. This eliminates the lash adjustments that used to be necessary. If an engine with hydraulic lifters truly has no oil pressure, the lifters will quickly collapse, and the huge gap will sound like one of those fairground BB guns, until the engine eventually seizes from the now-dry lower end welding itself together and the pistons welding themselves to the cylinder walls. Oil pressure serves as sort of a thermometer of engine health. Low oil pressure usually means some clearance is too large and is giving the pressure an easy way out. High oil pressure can indicate sludging, although it's not nearly as serious ans low oil pressure, and the oil pump has a spring-loaded check valve that prevents pressure from going too high.. Unless you've had some sort of catastrophic failure of the lubrication system, oil pressure is lost gradually as the engine wears. If you have oil on the dipstick where it should be, and the engine is running quietly and smoothly, it's almost certainly a failure of the oil pressure gauge or related wiring/sender. To me, it sounds like an electrical fault. I personally like to have a gauge because it can warn you of problems before they become extremely serious, and gives me something more accurate other than the idiot light to let me know what's up inside the engine. It's like a temperature gauge-- 98% of the time you don't need it because it just says that everything is OK and normal, and the other 2% of the time, you're glad you have it.
Sorry about the long-winded post, I always like to have at least a general description of what a part or system does before I try to troubleshoot it so I can picture what's going on.
 

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The proper way to diagnose this is to attach a mechanical oil pressure gauge to the engine temporarily to verify oil pressure is good. However, the sending unit is inexpensive enough I'd just replace it because if you really had an oil pressure problem for that long the engine would probably be making some bad noises. You probably need a special socket for the oil pressure sending unit.
 

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Discussion Starter #6
Wolf, Crown, B10, and Valiant, all excellent responses and I thank you all very much for taking the time. That's why I like this forum so much. Helpful people!

I will install a new pressure switch. The car really does run just fine, so that is hopefully all it needs.
 
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