Erratic Oil pressure- gauge/pressure

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mgcjag
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#21 Re: Erratic Oil pressure- gauge/pressure

Post by mgcjag » Fri Aug 28, 2020 4:28 pm

If you can see a definate change then something has to be opening/closeing to make the change...so pressure relief valve...if you search Jag Lovers there are posts where some of the guys actually calculated the opening closeing pressure of their springs after dismantling and measureing replacement springs....Steve
Steve
1969 S2 2+2 & Building a C type replica

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#22 Re: Erratic Oil pressure- gauge/pressure

Post by mtnjag » Fri Aug 28, 2020 4:43 pm

Yes, that's what I figure as well. It definitely appears to be opening and that's fine. The question is why the variation up and down in pressure after it opens. Never did it before. One would think that it would open and stabilize at a certain relief point at a given rpm. Always did before I guess because the gauge did not show erratic 5-10# swings up and down.
Layne
Car #876005, 62 OTS

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#23 Re: Erratic Oil pressure- gauge/pressure

Post by mtnjag » Fri Aug 28, 2020 9:33 pm

I think I have solved the problem/mystery. Find out for sure when I go on a test drive tomorrow.

Appears to be alignment of the cylinder/valve body in the housing. We shall see.
Layne
Car #876005, 62 OTS

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#24 Re: Erratic Oil pressure- gauge/pressure

Post by mtnjag » Sat Aug 29, 2020 4:20 pm

As it turns out it does appear to make a difference how the cylinder/valve body is installed in the housing.

Although there is no obvious index mark or keyway or anything requiring it to be aligned properly, good sense would indicate that one of the 4 holes in the valve body should be aligned with the pressure relief outflow return opening to the pan. You must look up into the cylinder to see that this is the case. It is then held at that position by the pressure of the gasket and cap.

It is entirely possible, and was the case here, that the 4 holes were perfectly off the opening. Resulting in much less flow to the bypass outlet. So my guess is that it resulted in the valve opening but not with enough flow under pressure to maintain a constant opening. The cylinder is a very close fit in the housing with no relief around it to allow oil to circulate at good flow and make it's way out easily without the hole being aligned, as it would be in a banjo bolt fitting. Therefore, it would open and close, at least partially while my max pressure was slightly higher as well as it couldn’t relieve fully. And there is the fluctuation.

The gasket had been leaking and in replacing it I cleaned everything up very nicely and must have reinstalled it in a wrong position-probably better than a 50/50 chance. There is a small hole on the bottom face of the valve that aligns with one of the relief holes up in the body and if that is aligned with the outflow pipe or at 90/180/270 degrees from the outlet will align a hole properly but I had no idea of this. The XJ6 shop manual does not remark on alignment at all. It only makes sense but one would think if it was important there would be a key or a flat or obvious mark indicating alignment.

I did this more than once! Although the valve was my logical suspect I repeatedly could not find anything “wrong” with it.

So the problem turned out to be Mr. Mechanic/the nut behind the wheel!
Layne
Car #876005, 62 OTS

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#25 Re: Erratic Oil pressure- gauge/pressure

Post by mgcjag » Sat Aug 29, 2020 4:35 pm

Well done Layne...glad that you sorted it.....one area of modification to an E type that probably dosnt need modifying.....Steve
Steve
1969 S2 2+2 & Building a C type replica

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#26 Re: Erratic Oil pressure- gauge/pressure

Post by Tom W » Sat Aug 29, 2020 5:21 pm

Glad it’s sorted. What oil pressure are you seeing now?

I think the single hole is only to let oil out of the cavity beneath the plunger. Without it, there’s a chance the valve could hydraulic lock as it was pressed down.
Tom
1970 S2 FHC

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#27 Re: Erratic Oil pressure- gauge/pressure

Post by mtnjag » Sat Aug 29, 2020 5:27 pm

I'm back where I was. About 60# at 2500+ once warmed up well, doesn't go over 70# whether high rev or cold. No fluctuation that's noticeable. Pressure comes up and then rather than a drop and a rise it simply doesn't go any higher. Kick myself but glad it was a simple solution to what was a disconcerting issue.
Thanks.
Layne
Car #876005, 62 OTS

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