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GH85Carrera's Avatar
 
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Chevy small block weird oil pressure readings.

OK this one has me scratching my head. The trusty El Camino has a base 350 crate engine from GM and 71,000 miles on that engine and flawless running. Heads have never been off, and no engine changes or mods at all, except the ancillaries like the alternator and such. After a grand total of 371,000 miles on the car and 29 years of driving it I know the normal sounds it makes.

We are not cold around here as yet, but the other morning the car was in the garage at 50 or 60 degrees. I went on a short errand and the oil pressure gauge only is calibrated or numbered to 60 PSI, and the needle was pointing to 70 or 80 PSI. I could hear a slight tapping sound much like a minor exhaust leak. Later I checked the exhaust manifolds and all was tight.

I run 10-30 Brad Penn oil as it it is a flat tappet engine. Once it fully warmed up, all was normal and the gauge showed 25 to 30 PSI at idle and went up as RPM increased. Oil level is 100% normal.

If there was not an RPM based tap tap tap, I would just replace the sender. The noise is the mystery. Once the engine is warm, no tapping sounds, and all is normal. I just returned from a 40 minute round trip and everything was just normal.

Any suggestions on a likely cause of high oil pressure and tapping sounds?

I have not done any work at all in the engine compartment in months.

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Old 10-07-2020, 01:47 PM
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This happened once?
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Old 10-07-2020, 02:55 PM
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Twice so far.
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Old 10-07-2020, 02:59 PM
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Change the filter?

Or the oil pump...that seems really unlikely.
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Old 10-07-2020, 03:01 PM
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2,100 miles since last oil change. It is not even black yet.
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Old 10-07-2020, 04:37 PM
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Bad oil filter?
Old 10-07-2020, 04:42 PM
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restricted or plugged oil passage to a lifter?
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Old 10-07-2020, 04:43 PM
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Stuck pressure relief valve would be my guess, but I haven't messed with a SBC for a long time.
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Old 10-07-2020, 05:03 PM
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Sticking relief valve in the pump body possibly. But I can't say why there would be noise associated with it. Hmmmm
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Old 10-07-2020, 05:14 PM
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Stuck relief valve would be my guess too. But I'd also check/replace the filter. Make sure its a quality one.
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Old 10-07-2020, 05:17 PM
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Chevy small block weird oil pressure readings.

Relief valve just sticking after 71,000 miles with regular oil changes and super clean oil, no sludge. Quality oil filters always used.

Possible but how would that happen?

I will do an oil change early just to eliminate that. And I will cut open the filter to inspect.
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Old 10-07-2020, 05:56 PM
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I once had a '68 BMW 1600 that had a relief valve stick. It is really eye opening when you see a spin-on oil filter move away from the mounting flange as you rev the engine really gently so it doesn't blow off all of a sudden. Displacement oil pumps put out a lot of pressure with very little effort.
I think I would start diagnosis with replacing the oil filter. Cheap and easy, and it might solve the problem for you.
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Old 10-07-2020, 05:59 PM
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Quote:
Originally Posted by GH85Carrera View Post
Relief valve just sticking after 71,000 miles with regular oil changes and super clean oil, no sludge. Quality oil filters always used.

Possible but how would that happen?

I will do an oil change early just to eliminate that. And I will cut open the filter to inspect.
Isn't there a relief valve in the filter?
Could just be a bad filter, law of avg's on getting the one in a million that goes bad.
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Old 10-07-2020, 06:01 PM
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You mentioned it's happened twice. Does that mean intermittent? Are there times since the first spike when starting cold that there has been no spike?
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Old 10-07-2020, 06:10 PM
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I would also want to see a mechanical gauge reading. Or a second reading to confirm.
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Old 10-08-2020, 05:44 AM
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The two times it happened were conditions similar ? Engine temp/ambient temp/RPM's etc ? For the minimal investment I'd try some Marvel Mystery oil , drive it a few hundred miles and then do an oil/filter change . The oil you are using is excellent stuff so I doubt that is the problem .
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Old 10-08-2020, 06:07 AM
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I use a oil filer made by WIX. It is a high quality oil filter.

When I pull the dip stick after 2,100 miles I have to catch a reflection to even see the oil level on the dip stick. It never gets black, just the green color of the Brad Penn and it is a pretty thin layer on the dip stick.

My first thought was the gauge or sender or wiring was dead. It is a bit of a pain to replace the gauge, as the instrument bezel has to be disassembled. I have replaced the sender once when it showed really low oil pressure but that has been 6 or 7 years ago. The new sender fixed that. If there was no tapping noise, I would just happily ignore it until I have time to test the sender or the gauge.

I have only driven the car twice since I noticed the issue. I will know more shortly as I need to go somewhere and I can watch the pressure gauge closely.

The oil pressure running high is one issue, but what is the tap tap noise that perfectly mimics the sound of a leak at the exhaust manifold? It goes away as soon as the pressure drops to normal. And the manifold bolts are tight, that was the first thing I checked.
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Old 10-08-2020, 06:31 AM
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Quote:
Originally Posted by GH85Carrera View Post
The oil pressure running high is one issue, but what is the tap tap noise that perfectly mimics the sound of a leak at the exhaust manifold?
Not discounting the correlation between high pressure and tapping with what I'm posting here. Just talking.

I did have a 1995 Odyssey. The little ones with the 4cyl engines. The exhaust manifold had a crack in it and would make the noise when cold and once warm it expanded and sealed itself off. I could not see it from casual observation. It was underneath.

Maybe one of those mechanics stethoscopes to isolate noise?
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Old 10-08-2020, 08:05 AM
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Could it be a lifter not getting oil?

I had a car that made the exhaust manifold leak sound until it warmed up as well.
Old 10-08-2020, 08:09 AM
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Quote:
Originally Posted by GH85Carrera View Post
I use a oil filer made by WIX. It is a high quality oil filter.

When I pull the dip stick after 2,100 miles I have to catch a reflection to even see the oil level on the dip stick. It never gets black, just the green color of the Brad Penn and it is a pretty thin layer on the dip stick.

My first thought was the gauge or sender or wiring was dead. It is a bit of a pain to replace the gauge, as the instrument bezel has to be disassembled. I have replaced the sender once when it showed really low oil pressure but that has been 6 or 7 years ago. The new sender fixed that. If there was no tapping noise, I would just happily ignore it until I have time to test the sender or the gauge.

I have only driven the car twice since I noticed the issue. I will know more shortly as I need to go somewhere and I can watch the pressure gauge closely.

The oil pressure running high is one issue, but what is the tap tap noise that perfectly mimics the sound of a leak at the exhaust manifold? It goes away as soon as the pressure drops to normal. And the manifold bolts are tight, that was the first thing I checked.
Seems before you start tearing the dash out and replacing gauges, you could spend $40 on a mechanical aftermarket gauge and put it in place for a short time for testing.

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Old 10-08-2020, 08:11 AM
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