Oil Pressure Idiot Light

[VerbotenZ34]

Ok you mavens of 3.4DOHC knowledge, I've got another maintenance question for you!

Last night, I drove approximately 30 minutes to the 'party' district of my city. On the way there, the car was operating normally.
When I left the district, my oil pressure gauge fell right off the scale and gave me the idiot light! So I immediately pulled over, fearing that while sitting I had somehow lost all my oil! The oil level on the dipstick was within tolerances, a little on the low side perhaps but not a matter of concern.
I thought it was simply a matter of the guage wonking out on me, so I drove home (in retrospect, probably a dumb idea if the guage is telling me 0kPa). On the way home, the guage picked up into the midrange of the scale when revved over 1000PRM. At idle the guage dropped and flashed the idiot light - so I always kept it at ~1000RPM. Also, on the way back home I noticed that the scale would only drop if the engine was engaged in gear - park or neutral would allow the guage to remain at ~137kPa (or 1/4 on the scale).
Anyways, got her home and thought it was a clogged oil filter or a wonky guage/oil pressure sender. I decided to do an oil change the next morning.
The next day I changed out the oil and filter, and started it up to see if the condition still existed. The car started, ran fine for a lenghty period of time (just idling in my garage), and when it started to get hot the guage began to steadily lose 'pressure' until it dropped and gave me the idiot light again. It was at this time that I also noticed that my coolant temp gauge was reading high - about midrange on the scale, which is higher than usual even after a long drive.

So it seems that the guage reads fine until the car has been operating for a time and gets 'hot'. Has anyone experienced a similar problem? I hope its just the sensor, as I have no way of telling if there's actual oil pressure in the system without taking it in to a shop.

Thanks in advance for any troubleshooting tips you guys might have! And sorry for the lenghty post - just want to give everyone all the information
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[93LuminaZ34va]

Have you switched the weight of your oil? My Camaro runs 60 PSI, even at idle, untill its warmed up. Then it comes on down to 30, but never higher. My Grandma's old Cutlass supreme (old 3.8l motor, before the 3800 revision) would always at idle run about 15 psi..... which I always thought was low. Try a thicker oil, find out the resistance scale on the pressure sender you are using and test it..... Other than that, a clogged screen on the oil pickup, or some serious internal problems will result..... I hope its just the sender on the way out!

[dohcfiend]

don't mean to scare u but i had a 2.8 fiero that did that and it ended up being ther bearings. i don't if they were the cause but they were the result.

does the light also come on when u brake for a stoplight?

[VerbotenZ34]

Have you switched the weight of your oil?

Hmmm, no. The oil weight I changed out the old stuff for was the same brand and weight,...?

don't mean to scare u but i had a 2.8 fiero that did that and it ended up being ther bearings. i don't if they were the cause but they were the result.

Consider me scared!

does the light also come on when u brake for a stoplight?

Yes, whenever the car is idling in gear (drive or reverse) the guage drops off the scale and throws the warning light. Idling in park or neutral has no effect on the guage when the engine is 'cool', but will cause the guage to drop off the scale when the engine is 'hot'.

This bad boy's going into the mechanic on thursday, since he has skills and training I don't. Hopefully he's able to diagnose the problem accurately,...
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[93LuminaZ34va]

Just making sure you hadn't switched to a thinner oil. That would affect the pressure some, depending on the shape of the internals of the engine.

[VerbotenZ34]

Going to replace the sending unit on my day off this week - we'll see if that fixes the problem,...

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