I have a 00’ C-5 with 51,000mi on the clock. I have been the only driver and wrench since it had 24,000mi and from 24k until I rolled over 50k there were no significant issues with the car.

About 10 mo. ago, while crusing at 50 mph, the "check gauges" warning came on and it was followed by "low oil presure" warning. A quick look confirmed the message. I shut off the motor, coasted off the side of the road and I checked the oil level, finding it to be on the full mark, I restarted the motor and drove off. During the next 3-4 months the condition did not return and I finally wrote it off as a defective OPS unit. Then it happened again….same type of conditions; and again, when I restarted the motor the gauge functioned and everything returned to a “normal” state.

Last November (about 10 months from the initial problem occurrence) I replaced the cam, intake manifold, full exhaust system, and oil pump (ported and shimmed LS-6 pump from Texas Speed). I added a new OPS (remotely mounted) and added a mechanical OP gauge ahead of the sending unit. When the motor is cold, both the dash gauge, and the new mechanical gauge, read about 65psi at start…..after warming , the pressure drops to about 40psi under normal driving conditions.

Unfortunately, the same condition returned within about 50 mi after I put the car back on the street. Almost exactly the same as before I swapped parts in the motor. When the warning sounds, the dash gauge drops to almost nothing (10psi or less) while the mechanical gauge reads a little higher (around 15-20psi.). Both gauges recover and bounce back to around 40psi within about 10-15 sec.; but, they both still drop pressure..

There is not any pattern to when it occurs…. straight and level driving, no turning , no hard acceleration; but, it has happened at least 4 times in 400miles (since returning to the street). The motor is completely dry, does not consume oil (5w/30 Mobil 1), and does not make any unusual noise ( no lifter or oil starvation sounds); although I am watching closely and get the load off the motor within seconds of the warning….I am pretty sure the o-ring on the pick-up tube was correctly positioned and correctly installed.

This is frustrating and I am not looking forward to tearing down to replace the oil pump…again unless there is no other good options…..does anyone have any suggestions regarding the probable cause for this problem????

 

 

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You say your mechanical oil pressure gauge reads about 15 to 20 psi when this low oil pressure warning light comes on and you I'm dash oil pressure gauge reads low (10 psi or less) when this is occurring is the car at idle or what?

 

You did say you have an oil pressure sensor relocation kit right?

Also are you getting any diagnostic trouble codes such as P0522?

 

Yes, I did relocate the oil sender (new unit) in Dec. and added a "t" with a mechanical gage ahead of the OE sender. There does not appear to be any pattern to when the problem occurs and there are no codes.

 

The owner's manual states that you can add up to one additional quart of oil to the crank case for road racing, I recommend you do. If the problem goes away with the increased oil level it could be indicative or a problem in the oil pump pick-up tube.