Erratic Oil pressure- gauge/pressure

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mtnjag
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#1 Erratic Oil pressure- gauge/pressure

Post by mtnjag » Thu Aug 27, 2020 12:07 am

My mechanical 0-100# oil pressure gauge and apparently the actual oil pressure at the top end has a 5-10# erratic fluctuation over 60#. A recent development. NOT an electric gauge. 62 Etype, 3.8

Any suggestions taking the following into consideration are much appreciated.

*It was running without fluctuation with the following parameters:
-3.8 with about 10K miles on it.
-High volume oil pump.
-Normal hot oil pressure is about 60-65# creeping up to 70# at high rpm
-Running Jag EBC 9658 filter as well as others
-VR1 10w30 oil, up to correct level, very clean
-Mechanical gauge tapped into the block oil galley after oil filter
-XJ6 SIII spin on filter housing with oil cooler
-No leaks

*Condition
-A short time ago I was driving on the freeway at about 70-75mph and noticed the gauge needle fluctuating as indicated above.
-At a lower rpm, 2200 or so, pressure is 60# and steady with no fluctuation, bring rpm up, pressure rises to 65-70# and I get a 5-10# needle fluctuation
-Based on my tests what I originally thought was a gauge issue turned into an actual pressure issue.


*My investigation-one item at a time with a test between:
-No Change-blew out line from gauge to block
-Placed another mechanical test gauge on the next tap on the galley and ran engine with both gauges connected. It matched pressure and fluctuation of the existing gauge in car. Therefore concluded it is not the gauge but an actual fluctuation of the pressure in the range indicated.
-No Change-Changed filter to a new Jag filter, then to a WIX
-No Change-Disassembled oil pressure relief valve. Cleaned (it was clean), replaced “O” ring on steel cylinder, checked barrel (smooth), checked piston (smooth), very little wear indicated by marking, inspected inside from under car with light and looked clean with no crap anywhere.
-No Change-replaced pressure relief valve spring with NOS Jag spring.

*I would suspect either the oil pressure relief valve in the filter housing or the bypass valve in the filter but don’t know why that would start behaving like this all of a sudden and don’t understand why it would fluctuate vs. smoothly relieving the pressure.
Last edited by mtnjag on Thu Aug 27, 2020 2:32 am, edited 1 time in total.
Layne
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#2 Re: Erratic Oil pressure gauge needle/pressure

Post by abowie » Thu Aug 27, 2020 2:31 am

mtnjag wrote:
Thu Aug 27, 2020 12:07 am


*I would suspect either the oil pressure relief valve in the filter housing or the bypass valve in the filter but don’t know why that would start behaving like this all of a sudden and don’t understand why it would fluctuate vs. smoothly relieving the pressure.
I think you're correct. 70psi is a little high and what you are seeing is the overpressure valve opening and closing as it cuts in and out.

You could try replacing the spring, or pull out the old one and stretch it a bit longer.

Regardless, what you are seeing isn't likely to damage your engine.
Andrew.
881824, 1E21538. 889457..oops. Jezza the V12 XJS race car.
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#3 Re: Erratic Oil pressure- gauge/pressure

Post by mtnjag » Thu Aug 27, 2020 2:38 am

Thanks, just edited my original post to note it's actual a pressure issue and not just a fluctuating needle, thought I was a little unclear. But you got it.

Actually that is one of the things I tried. As noted I replaced the existing spring with a NOS Jag spring in original factory sealed parts bag which actually matched the one I pulled out exactly.

So you're suggesting to stretch it to raise the relief pressure if I understand properly.
Could also slip in an additional washer or two?

So that was also a feeling I had-that although there is an actual fluctuation in pressure it is up at a high pressure with plenty of flow left for adequate lubrication?
Layne
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#4 Re: Erratic Oil pressure- gauge/pressure

Post by Tom W » Thu Aug 27, 2020 6:33 am

This is puzzling. I’m not sure adding washers or stretching the spring is the right answer.

The oil pump creates flow. Oil pressure is generated as there’s a difference in rate at which the oil can flow out of the bearing clearances, compared to the rate the pump supplies it. The pressure relief valve is there to cap the oil pressure, otherwise it would rise continually with increased RPM. Above a certain point, it will always be flowing some oil.

For a healthy life, your engine needs the appropriate oil pressure and flow. More of either is not necessarily better, particularly if it’s at the expense of the other.

What condition is the oil cooler bypass valve in? How have you mounted the cooler? Which way up is it, and how high compared to the filter head? Have you added an oil cooler thermostat too, or is it without as per the XJ6?

How quickly does your gauge react? There may be some delay and damping between what’s actually happening in the engine, and what’s seen on the gauge.
Tom
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#5 Re: Erratic Oil pressure- gauge/pressure

Post by mtnjag » Thu Aug 27, 2020 1:58 pm

Yes, understand what you're saying about flow, pressure, and purpose of pressure relief valve. And yes, it is puzzling.

Please keep in mind-all was normal since eng installed, no changes, this just began happening.

So packing the relief valve may only raise the relief pressure with possibly the same issue occurring. It may be interesting/useful to see if the movement would occur at the same 65-70# or at the new raised limit of the pressure relief valve with the packing??

Oil cooler bypass valve-not familiar with the circuit. This is a stock XJ6 SIII oil filter head with cooler and has the push in cooler hose connections to the head with the clamp holding in the fittings. Large hose, not sure of size but my guess is -12 AN with Earl's AN fittings

Cooler is is mounted in front of radiator, at bottom on the aluminum shield in horizontal upright position with hose fittings facing up. Slightly below filter head. No additional thermostat, as per XJ6.

Gauge has been and is sensitive to rpm changes when below what I would call it's running pressure of 60-65# but in a smooth manner moving with rpm in the lower ranges. Never a jerky erratic motion previously or now. That does not occur until up at that 65# region. And that jerky motion is at a steady rpm, say cruising on the highway.

The erratic movement is not a damped motion. It is a quick jerky motion of 5-10#s. This was duplicated by the test gauge I inserted.
Layne
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#6 Re: Erratic Oil pressure- gauge/pressure

Post by mtnjag » Thu Aug 27, 2020 2:44 pm

From what I can see in some old threads and an on-line search, it looks like the oil cooler bypass valve is the large brass colored screw on the bottom of the housing. Haven't been able to find an engineering blow up dwg but saw a few views of the open mounting face and a brief description of flow. I'm still somewhat confused on the flow through the chambers.

Do you think it's worth opening that up and making sure it's clean and is there anything to be aware of when doing such?
Layne
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#7 Re: Erratic Oil pressure- gauge/pressure

Post by Tom W » Thu Aug 27, 2020 2:51 pm

You’ve just replied as I’ve been writing this, so I’ll amend it to try and include answers to your question. As both gauges show the same behaviour, then I think you’re right to assume the it is representative of what’s happening in the engine. How many miles have you done on the engine before this started happening?

There are a few possibilities to investigate to try and get to the bottom of this.

I would look at the oil pickup. If the pump is drawing in air as well as oil, you’ll get a momentary reduction in pressure as the aerated oil is compressible. Air could enter the pump several ways. Possibly a loose joint on the pickup pipe, for example. Or insufficient oil in the sump exposing the pickup pipe. Your oil level might be right when the engine’s off, but if something’s blocking it’s return to the sump, eventually the engine will pump all the oil to the top of the engine. If it’s a loose joint, possibly it’s something that only vibrates and opens up at the RPM you’re seeing the fluctuations.

The cooler pressure relief valve in the XJ6 filter head is a simple spring loaded ball valve, but it’s a self contained cartridge, so you can’t do much with it. It’s accessed by removing the large brass plug, but on the filter head I have, in practice, it doesn’t look easy to remove the plug without destroying it. It operates at a low pressure differential, to minimise pressure drop across the cooler matrix. If this opens, you could possibly see a small change in pressure going into the engine. I don’t know if, in practice, the pressure differential to crack the valve open will be the same as the pressure to close it. Maybe at that speed your just on the cusp of the valve fluttering. For the valve to operate as designed in the XJ6, you need a similar pressure drop across the cooler. Using a matrix of the same size and number of rows is a good start, along with the same dia pipes. However, the slightly longer pipe run required on the E-type could cause a slightly greater drop.

The cooler and oil filter are both downstream of the pressure relief valve, so be careful trying to up the overall pressure with different springs etc. Both the filter and cooler will see the effects of this. Flow through the filter initially comes from the pump into the chamber with the oil pressure relief valve. From there it either goes back to the sump, or to the cooler. From the cooler it goes to the dirty side of the oil filter, and finally through the filter to the oil gallery and bearings. The cooler relief valve joins the chambers that connect to the inlet and outlet cooler pipes. It short circuits the cooler matrix when it opens.

Another option to investigate would be anything loose that would momentarily affect the rate at which oil could leak out of the engine. The timing chain tensioner being one example.
Tom
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#8 Re: Erratic Oil pressure- gauge/pressure

Post by mtnjag » Thu Aug 27, 2020 3:10 pm

I have about 10,000 miles on the eng without this happening. I am a gauge watcher and this just started occurring.

Understand concern on increased pressure. Already running up to 70# which I think is pretty high.

Leave the cooler bypass valve, for now anyway.

I'll pull the cam covers and make sure there isn't a rag or something blocking a return.

Oil level is where I have been running so that should be alright.

Have been leaving it for last but I'll drop the sump and take a look. Have cometic gasket on it so it won't be that bad. Check pickup and pipe status, anything loose or blocked. (It'll give me a chance to test my theory of being able to remove the pan without removing the harmonic balancer.)

Make sure everything is tight as they should be.

Thanks
Layne
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#9 Re: Erratic Oil pressure- gauge/pressure

Post by Tom W » Thu Aug 27, 2020 3:30 pm

Good stuff, hope you find the cause.

If you want to clean the cooler bypass valve, the best way is probably to remove the whole filter head and access it that way. It’s visible with the filter head on the bench, without removing the brass plug. The plug’s more for closing the access drilling that’s required to machine the hole for the valve to sit in, rather than regular servicing.
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#10 Re: Erratic Oil pressure- gauge/pressure

Post by mtnjag » Thu Aug 27, 2020 3:33 pm

Me too. Thanks for the good thoughts.

And removing the filter head is something I've thought of but wanted to leave it for last, access and all.

More tinkering today I guess.
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#11 Re: Erratic Oil pressure- gauge/pressure

Post by mtnjag » Thu Aug 27, 2020 11:06 pm

Did a little more testing today and I think it revealed the issue. Why I still don't understand or why it is now occurring when it did not exhibit itself before.

I removed the cap for the pressure relief valve and place a couple of washer in it to raise pressure slightly to see if it had an effect. It gave me another 5# before the valve opened. It also gave me a more distinct opening of the valve.

Pressure was steady as rpm increased, pressure reached 70# and there was an obvious opening of the valve at which point the needle exhibited the fluctuation until I dropped rpm and brought pressure back down. Needle was then steady, increase rpm and until it reached the opening pressure it was steady and then fluctuation once opening.

I ran it for a while and as the car warmed the rpm at which it reached opening pressure was higher and higher. And the point at which fluctuation took place did not occur at a specific rpm level but at the 70# pressure level.

So unless I am misunderstanding what's happening it appears the the relief valve is bouncing around somewhat once open??
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#12 Re: Erratic Oil pressure- gauge/pressure

Post by abowie » Fri Aug 28, 2020 3:06 am

mtnjag wrote:
Thu Aug 27, 2020 11:06 pm

So unless I am misunderstanding what's happening it appears the the relief valve is bouncing around somewhat once open??
I think that's exactly what is happening.

Remember it's an overpressure valve; it won't open until a mimimum trigger pressure is reached, and shuts again as soon as the oil pressure drops below the trigger pressure. So what you see is a sort of sine curve based around the trigger pressure. Which is what your gauge is showing.

The question though is why is this happening? Oil pressure over 60psi is not normal for an XK engine. We have built probably 30 or so engines over the last 10 years. We are fastidious, cut no corners and our machinist is the best one in town. Our engines make a maximum of 50psi hot and at revs, and that is what they are supposed to make.

I'm not sure what is causing your oil pressure to be so high. It might be your oil filter. You may have something blocking one of your oil galleries (suspect this if there's any evidence of silicone sealant being used on your engine). There may be something wrong with your oil. AS suggested above it may be some sort of effect caused by the oil cooler bypass or some other problem within your oil filter housing. I've not seen this before so I'm not really sure where the best place to start is.
Andrew.
881824, 1E21538. 889457..oops. Jezza the V12 XJS race car.
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#13 Re: Erratic Oil pressure- gauge/pressure

Post by abowie » Fri Aug 28, 2020 3:12 am

If you haven't changed out your oil filter that would probably be a good place to start.
Andrew.
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#14 Re: Erratic Oil pressure- gauge/pressure

Post by mtnjag » Fri Aug 28, 2020 3:29 am

Yes why? Oil pressure has always run at 60-65# since the rebuild without the issue. I believe i have seen other posts with engines running that and slightly higher pressure but could be mistaken.

I am running a high volume pump which may account for higher pressure?

Oil filter change-Please see my orig post as to what i have done. I currently have the third filter on it since this happened. Two different brands.

Is there a certain way the pressure relief barrel is positioned in the housing? That has been in and out.
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#15 Re: Erratic Oil pressure- gauge/pressure

Post by abowie » Fri Aug 28, 2020 5:22 am

It's certainly confusing and I don't know.

Maybe someone else will chime in.
Andrew.
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#16 Re: Erratic Oil pressure- gauge/pressure

Post by Tom W » Fri Aug 28, 2020 5:49 am

I see from your first post the gauge is tapped into the main gallery, downstream of the filter. In that case, the filter has nothing to do with the excess pressure you’re seeing. A clogged filter would reduce pressure.

Your high volume oil pump will do a couple of things. It will lower the rpm at which the pressure relief valve opens, and the oil pressure peaks. You’ll probably also see an increase in oil pressure at hot idle. If your high output pump is such that it exceeded the flow capacity of the relief valve, then you could see an increase in pressure at higher RPMs. This feels unlikely though, given the dia of the pipe, although the routing is somewhat convoluted on engines with an E-type sump and XJ6 filter head.

There’s something in your description I don’t quite understand yet. When you say the needle was steady until 70psi, do you mean a steady value, or the needle was moving steadily, not erratically?

Does the pressure vary in proportion to RPM until the gauge reaches 70?

I wonder if your pressure relief valve is sticking closed? Excess pressure is then required to open it, at which point the pressure then drops to an appropriate level, as maintained by the spring. When the valve closes again, the pressure it closes at is lower than the pressure required to open it, so you see a fluctuating gauge. It’s a while since I pulled an XJ6 filter head apart. Is the relief valve just a simple ball, or is there a plunger behind it?
Tom
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#17 Re: Erratic Oil pressure- gauge/pressure

Post by mtnjag » Fri Aug 28, 2020 1:10 pm

Thanks for staying with me on this.

When I say the needle was steady I mean it was not erratic. it is steady value at a given rpm.As revs increase pressure increases until it reaches what appears to be the relief valve opening level and then "bobs" around slightly if maintaining that rpm. Drop the rpm slightly, pressure drops, needle stops "bobbing" around.

The pressure does vary in proportion to RPM as you move up, pressure builds and vice versa.

The valve behavior you describe is what I visualize happening.That would seem to explain why the erratic movement at a steady RPM. One would think it would open and reach a steady state at a steady rpm. This erratic movement is a recent development. So why??

The valve is a spring loaded piston/plunger in a cylinder.There is a cylinder of steel with an outer diameter "O" ring that slips into the aluminum housing. It has slots at its top to allow oil to enter and exit.There is a hollow steel piston/plunger in the cylinder with the coil spring inside. Spring holds it up in the closed position. The spring sits in a "cap" on the bottom that bolts up to the alum housing with a gasket.The bypass hose fitting is on the side of the housing in a horizontal position and flows out and to bottom of pan through a pipe to stock Etype location.

My friend has another compete used OEM filter head. Thinking I may hit him up and get the valve assembly from him and replace the one in my head. See what happens.
Layne
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#18 Re: Erratic Oil pressure- gauge/pressure

Post by Tom W » Fri Aug 28, 2020 3:51 pm

That makes sense.

I would remove the oil pressure relief valve again and thoroughly clean all the parts. Polish the piston too. If you can remove the cylinder, I’d do so and clean and polish that too. Maybe there’s a bit of crud somewhere in there that’s causing the valve to stick. It needs to be able to slide freely with no stiction.

Remember the pressure relief valve is before the oil filter, so only sees dirty oil. Anything in the sump small enough to pass through the strainer and pump could make it through to the relief valve un checked.

On my car (standard filter head), maximum oil pressure is achieved around 2000-2500 rpm. Beyond that, the pressure relief valve must just open more.
Tom
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#19 Re: Erratic Oil pressure- gauge/pressure

Post by mtnjag » Fri Aug 28, 2020 3:55 pm

Yep, I'll check it thoroughly and polish it out. It does feel good already but I'll give it a go. Don't know about my friends. Hope to find out later today.
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#20 Re: Erratic Oil pressure- gauge/pressure

Post by Tom W » Fri Aug 28, 2020 4:20 pm

Yes, worth getting hold of as a comparison, and swapping out to see if it makes any difference.
Tom
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