Oil Pressure Gauge on 97 Aerostar

Today I noticed the oil pressure gauge showed no pressure. No idiot light was on and no weird noised. But just to be safe, I pulled off the road right away to check. Oil level was fine and no burning oil smell or leaks. When I started the engine again, the pressure came up right away to about 1/2 where it should be. Then after driving for 5 minutes, it came back to mid-scale.
Does this sound like the pressure sensor might be going bad or need cleaning?
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On Wed, 19 Oct 2011 22:05:13 -0700, "GuvBob"

on and no weird noised. But just to be safe, I pulled off the road right away to check. Oil level was fine and no burning oil smell or leaks. When I started the engine again, the pressure came up right away to about 1/2 where it should be. Then after driving for 5 minutes, it came back to mid-scale.

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For Fords of your Aerostar's vintage, the "sensor" is just an on/off switch. If the pressure is above the low pressure set point, the indicator ("gauge") jumps up to half scale or a little more (ususally somewhere between 50% and 75% of full scale). If the pressure is below the set point, the indicator ("gauge") drops to low (0). Since there is not an actual variable sensor, if the gauge appears to move around, you have either a bad switch (intermitent), a bad indicator ("gauge"), or a wiring problem (flaky connector, broken wire, etc). I suppose it is possible that the oil pressure is low and is fluctuating to just above and just below the switch's set point. If the switch was constantly cycling from off to on, I suppose it could casue the gauge to appear to be actually indicating changing pressure, but this seems unlikely. I can't imagine the oil pressure would be so low and variable that it would rapidly cycle the pressure switch for more than a few seconds.
Best thing for you to do is check the oil pressure with a real mechanical gauge. The Ford gauge on your dash is just a glorified indicator light. It is a positive indicator (i.e., it confirms you have enough or at least some oil pressure) versus the typical oil warning light which is a negative indicator (i.e., you don't have enough oil pressure), but it cannot be used to diagnose oil pressure concerns. You need a real gauge for that. And it is not just Ford that has this sort of arrangement......
Ed
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Thanks, Ed & Clare. Will have the shade tree mechanic (me) check this out.

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