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Unusual Oil Pressure
We've just been out for a run in the Cobra and I noticed that the oil pressure was dropping off as the revs fell and at tick-over, it was down to 10-15psi and it's never done that before. It quickly rose again as the revs increased and was at around 80psi at 2,000rom upwards. However, even that was inconsistent as sometimes it would be at 90psi and at others 60psi.
It has always had strong and consistent oil pressure, typically around 90psi and maybe dropping to 70psi at tickover. I've checked the oil level and it's right in the middle of the acceptable range. I've read various threads suggesting that pressures as low as 8psi is okay at tickover on an FE, but it isn't normally anywhere near that low on my engine, so something has changed. Oil temperature was around 170 degrees F. Can anyone shed any light on what might be happening? :confused: Paul |
Since you said it is 60 sometimes and 90 others, I would suspect the oil pressure gauge or the sender unit. Possibly a bad ground. Verify your pressure with a good mechanical gauge.
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Thank you for the input. However, the gauge responds emmidiately to engine revs. so I don't feel that it or the sender is the cause of the anomaly.
Could the pressure relief valve be causing this? Paul |
I think it might if it were sometimes hanging open after enough revs to increase pressure to where it opens. But unless it's picked up something to hang it, it's hard to figure this happening in something continually bathed in oil. However, 70 psi at hot idle is definitely unusual for a gear pump. Do you have a mechanical or electrical oil pressure gage?
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Certainly a PRV issue could cause a pressure change, but before I tore into my engine, I would make sure there was a real pressure change. The very first step is to verify that the oil pressure is indeed changing, as your gauge indicates. Or you can be like my brother n law. He replaced the engine in his wife's car, just to find out it had an empty gas tank. I learned a long time ago to assume nothing. It could be many things. You have to start somewhere and prove what is or is not. In your case, I would start by proving that the pressure gauge in the car is correct or it is not correct. Then move forward. But if you are looking for an excuse to tear into the engine don't let me stop you. |
The oil pressure gauge, along with all the others, is a Kirkham/Speedhut unit.
I've dropped the oil pan and taken off the oil pump. The pressure relief plunger initially felt as though it was jammed, but it moved freely enough now after spraying some cleaner in there and working it up and down a few times. However, for the price of a new 57HV pump, I'm tempted to just fit a new one. There was nothing inside the oil pan that wasn't supposed to be there, so I'm reasonably happy that there isn't something seriously amiss elsewhere in the engine. Many thanks for the input and advice. Paul |
I am more on the dark side, Paul. I suspect you have hurt something inside the engine and I would refrain from driving it until I had identified the potential problem and resolved it or determined there was no problem.
The easiest way to get an idea of what is going on (without pulling the engine) is to go to the Blackstone labs site order one of their free test kits. Put your oil sample into the provided container and wait for the results. The cost is about $25 - $30 and the results will either give you peace of mind or tell you it is time to tear it down and fix something. Ed |
If you have a problem of the magnitude where it does that to your oil pressure, no need in wasting time sending oil to Blackstone. Snag an oil filter cutter and cut the filter apart. If there's a problem, it will be very apparent in about 5 minutes time.
I think I'd try a different gauge first just for giggles, but an oil filter inspection will calm any fears. |
Good point ^ Brent. Blackstone is more of proactive tool before the carnage becomes massive. The oil filter is a quick and pretty reliable litmus test that should immediately show any mischief that might be going on.
If the oil filter shows clean, Paul, then I would go the Blackstone route. Sadly I suspect your oil filter inspection is going to confirm larger problems — for your sake I hope I am wrong. Ed |
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Good luck. |
Thank you. All sound advice.
The engine has run for over 25,000 miles with solid and stable oil pressure, so there is no reason to suspect that the pickup is too close to the bottom of the pan. I'll cut open the filter to see if there is anything in there. What is the recommended filter for these engines? Ferrari owners like Baldwin filters, but I've not read too much on here about filter preferences for our cars. Paul |
Wix 51515R.
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100% agreement with olddog, Paul. Use the old Reagan trust but verify model and you won't get bushwhacked.
Ed |
So has the oil pressure been verified with a mechanical master gauge as yet?
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No, but the behaviour didn't feel like a faulty gauge to me. I'm going to fit a new pump and see what that does.
Paul |
I think you should test the oil pressure with a workshop gauge first.
At least an accurate mechanical gauge. That would be a normal workshop procedure before jumping in and guessing an oil pump. Gary |
I've cut the filter open and there's absolutely nothing metal in there.
I'd have to reassemble the engine and run it to test the oil pressure, so it makes no sense to me to not replace the oil pump while I have it out. If, when I've fitted the new pump it still misbehaves, I'll check the pressure with another gauge. I've spun the pump on the bench with an electric drill and it doesn't sound particularly healthy. There is a definite knock and a tight spot. Paul |
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Just for grins take the pump apart to see what is amiss. While you have the pan down also check the rod bearing physically farthest from the pump. If the bearing looks good, count your blessings, put a new pump in and don't worry be happy. If the bearing show some scuffing and embedded particulate matter replace it and check the rest of the rods and mains for similar issues. If you have to replace two or more bearings just replace the entire set. Pay attention to the crank journal(s). If it (they) have become scuffed, your job just got bigger. At this point, based on what you have discovered so far, it sounds like you have side stepped a bullet — congratulations. BTW good Sherlock Holmes work ... Ed |
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