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Discussion Starter #1 (Edited)
Please help -- I need a sanity check and any advice would be appreciated!

On my 05 Pathy, it indicates low oil pressure when the engine is warm, and the engine is running at idle speed. The needle reads below L on the gauge and the warning light turns on.

When the engine (and oil) are cold, the needle reads midway between L and H. This has not changed. But as the car warms up, the idle oil pressure drops. Still, when the engine is revved, pressure rises -- so at around 2000RPM, oil pressure reads around 30%-50% on whatever scale the gauge is indicating.

While driving, even though the warning light turns off, the oil pressure is lower than it used to be, and probably should be.

The engine is running extremely smooth, no signs of rough idle, knock, valve noise, etc. Dealer service had car, replaced the sender. I don’t think that this is an electrical issue since the gauge reads properly when oil is cold. Dealer tech wanted six auth hours of labor to debug wiring harness and dashboard lights/gauges. Since the gauge reads consistently, and it shows the oil pressure as OK when car and oil are cold, I would conclude that the gauge and lights are in working order.

Somehow I think this is related to oil, either viscosity breakdown or flow impedance. Nissan service says car OK to drive, I think he’s nuts, but I have it in writing.

Anyone have any bright ideas? I want to attack this logically. Am I crazy for thinking this is a problem that needs to be fixed, or am I worrying too much? Any other details you guys could use let me know and I’ll check it out.

Facts:
  • Idle speed at 625 RPM
  • Oil level OK
  • 5W-30 motor oil (non-synthetic), Nissan Filter
  • Oil change did not improve/change oil pressure.
  • Engine runs great
  • Coolant level OK

Other issues with car:

Dealer pressure tested radiator and found coolant leak at rear climate control device. Not a severe leak, but drips on exhaust. Thought was blown head gasket b/c of smell. May have another coolant leak in front of vehicle near secondary reservoir, but I am not 100% sure.

I think strut/swaybar is going. Low speed rolling causes slight clunking felt thru floorboard.
 

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Did they happen to hook up an oil pressure gauge and double check the oil pressure?

There is a procedure in the ESM for troubleshooting. Basically, you unhook the factory sender, and hook up an oil pressure gauge and get readings that way.

Good luck!
 

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Discussion Starter #4
oil pressure is biased low. warm idle 6-8 psi, 2500 rpm is around 45-50 psi (hard to push gas and wife read dial without measurement error)
 

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Discussion Starter #6
I'm x-posting this at another forum, too.

In case anyone's interested to comment, I'm investigating the following before I go after the oil pump (which equates to open-heart surgery...and I'm no more than a glorified male nurse).

I'm ASSuming the pop-off/relief valve in the oil pump is working correctly, since I get good oil pressure 40-45psi when the engine is cold, and the pressure will not go beyond 50psi when rev'd.

That leads me to think that this is a flow or viscosity issue.

So if it's a viscosity issue, I'm going to try flushing the cooling system. It's a long shot, but it makes sense to me: Higher temperature in a fluid causes lower viscosity making it harder to pressurize. The '05 has a secondary oil-cooler, and I've said earlier I had a small, under-control, coolant leak in the rear climate control system. If air or gunk has deposited itself in the oil cooler, it would decrease its performance, resulting in lower oil viscosity, thinner oil, and lower oil pressure. I see no cross-contamination in either the oil or the coolant.

Since this has a radiator and an aux tank, do I (and how would I) burp the system?

I'm also going to trade-up to 10W-30 oil for the viscosity boost.

If it's a flow problem, I have to get into the oil pan and check the strainer. I'm not excited about this job, it's 20 deg, snowy, and I don't have a garage...but I'll pop the lower pan off and see if there's a lot of gunk on the strainer.

Any thoughts or bright ideas? Thanks for replying
 
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