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Fluctuating Oil Pressure
https://www.ausmini.com/forums/viewtopic.php?f=2&t=83517		 Page 1 of 2
Author:  Cooper_Matrikon [ Sun Nov 17, 2013 2:34 pm ]
Post subject:  Fluctuating Oil Pressure
I'm wrestling with an oil pressure worry with Barney at the moment. Running pressure had been sitting on 50psi for the past 3 or so years and just before Rylstone this year, dropped to a needle width under 50.

In the last few weeks, I'm now seeing massive fluctuations in oil pressure. Starting up at 48, holding for a while and then dropping as low as 30 odd at 90ks, then coming back up to 48 when I slow down.

Spent the last few days chasing oil leaks and replaced the timing chain cover seal and gasket as well as the gasket behind the front engine plate. Oil leaks cured, but I've just been out for a run and the pressure is back to crazy mode.

I've oscillated between KMX 20/50 and other brands, but I would not have expected such wild fluctuations in pressure. I've also replaced the copper oil pressure lie with nylon and new olives.

Before I start the rebuild thread thinking its bearings, can I rule out the gauge being faulty or anything else silly/simple? I would have thought that if oil pressure was low, even at temperature, it would stay low and not return. Either way, my guts is in a knot.

Evan
Author:  phillb [ Sun Nov 17, 2013 3:53 pm ]
Post subject:  Re: Fluctuating Oil Pressure
Two things I would check.

1. Remove the pressure relief valve and check for damage. If it is the original bullet style they can get stuff stuck in them and jam resulting in erratic readings. Mine would jam closed and the oil pressure guage would go off the scale (100+ psi) or jam open and result in low reading.

2. Remove the gauge. If you look into the fitting at the back of the gauge there is usually a fine filter. Somtimes this can be clogged. Can be gently cleaned with a needle.

Might be worth trying a different gauge also.

Like others have found the KMX seems not as good as it used to be. I've found the Valvoline Classic a good oil.

When the car is dead cold and you start it up what sort of pressures are you seeing?
Author:  Cooper_Matrikon [ Sun Nov 17, 2013 5:01 pm ]
Post subject:  Re: Fluctuating Oil Pressure
Straight to 48-50psi on old start up. The bit that confuses me is the fact that it will run at 25-30 at speed (80-90k) and then come back up to 48ish when I slow down. If its bearings would it not stay down?

It has the ball bearing relief valve and I checked it a while ago. Hmmmmmm.
Author:  phillb [ Sun Nov 17, 2013 5:23 pm ]
Post subject:  Re: Fluctuating Oil Pressure
It does sound odd. Would be interesting to try a different gauge.

Also interesting to try with the standard oil pressure relief setup just to see what happens esp checking the spring is correct length etc.

Interested to hear others opinions.
Author:  drmini in aust [ Sun Nov 17, 2013 6:33 pm ]
Post subject:  Re: Fluctuating Oil Pressure
With the ball... I think I fitted that when we had the car but I can't remember.
Is the spring straight? If not buy a new S one, if bent they can push the ball sideways when it's off the seat. Then pressure goes south. The 9/16" ball is a lot smaller diameter than the plunger is.
And also is there a bit of 5/16" diameter steel rod inside the spring? If not cut a piece 40mm long, deburr the ends and fit it, this helps keep the spring straight for the reason above.
Author:  MattE [ Sun Nov 17, 2013 8:11 pm ]
Post subject:  Re: Fluctuating Oil Pressure
Have a look at this thread.
Doc offered me similar advice re: the spring support, and it sorted me right out.
Would have pulled the engine down otherwise!

viewtopic.php?f=2&t=80568

Might be worth a try for the little effort involved....

Cheers
Matt
Author:  DaveMini [ Sun Nov 17, 2013 8:41 pm ]
Post subject:  Re: Fluctuating Oil Pressure
Why are you running a ball and not the correct relief valve. Talk to any hydrylic expert and they will bag the idea of using a ball. I cannot correctly relate what occurs when using a ball but it is not what was originally designed to happen if using the correct relief valve.
Author:  drmini in aust [ Sun Nov 17, 2013 8:49 pm ]
Post subject:  Re: Fluctuating Oil Pressure
Ball seals better when seated, it is hardened and the seat is not, so the seat gets shaped to fit. You get better oil pressure at idle (no leakage). The plunger does not seat well unless it's lapped in, and they seldom are.
There is also the story spread by suppliers and others that the 9/16" ball was used in the Cooper S. I have owned a few S motors over the years and never found one. it may have been a homologated part for competition, I dunno.

I currently use a ball, it works fine when fitted as I described above.
Author:  DaveMini [ Sun Nov 17, 2013 9:21 pm ]
Post subject:  Re: Fluctuating Oil Pressure
The problem with the ball is that when it is off seat, the area change is not linear as with the valve.
I understand the advantage of the ball in that it is hardened and that the valve and seat are never matched properly. That is why the ball may have worked in early days, also would have had a greater seat pressure thus masking other oil pressure issues. There are many interesting stories.
I used to be a "ball" person until the functional operation of the valve and seat was described to me. I always use a new valve and spring these days.
Author:  Cooper_Matrikon [ Mon Nov 18, 2013 8:03 am ]
Post subject:  Re: Fluctuating Oil Pressure
So I've had the spring, ball and rod out. Spring is not bent, though is worn flat, moreso at one end. The little rod is also a little worn, more oddly shaped at one end too. Put it all back together and it oil pressure drops still. Will idle at 50. Rev and it drops to 25/30. Obviously gets worse the hotter it gets.
Author:  Cooper_Matrikon [ Mon Nov 18, 2013 8:08 am ]
Post subject:  Re: Fluctuating Oil Pressure
With the symptoms described, am I likely looking at the cause being something simple and fixable or is disaster imminent? As I said the bit that gets me is that the oil pressure returns when revs drop. If bearings or similar were worn, then wouldn't the oil pressure just stay low at temp?
Author:  sitnlo62 [ Mon Nov 18, 2013 8:49 am ]
Post subject:  Re: Fluctuating Oil Pressure
DaveMini wrote:
The problem with the ball is that when it is off seat, the area change is not linear as with the valve.
I understand the advantage of the ball in that it is hardened and that the valve and seat are never matched properly. That is why the ball may have worked in early days, also would have had a greater seat pressure thus masking other oil pressure issues. There are many interesting stories.
I used to be a "ball" person until the functional operation of the valve and seat was described to me. I always use a new valve and spring these days.


Yes Yes :!: :D :D

I have been of this opinion for Thirty Years and finally someone has the courage to put it in writing.
You are spot on DaveMini, love your work :D

Dave
Author:  phillb [ Mon Nov 18, 2013 9:36 am ]
Post subject:  Re: Fluctuating Oil Pressure
As suggested previously order a new standard valve and new spring and fit. See what happens.

Perhaps the ball is a good seal at idle but then opens too much under pressure.

The ball mod can give odd results.


Sent from my iPhone using Tapatalk
Author:  drmini in aust [ Mon Nov 18, 2013 9:51 am ]
Post subject:  Re: Fluctuating Oil Pressure
Cooper_Matrikon wrote:
With the symptoms described, am I likely looking at the cause being something simple and fixable or is disaster imminent? As I said the bit that gets me is that the oil pressure returns when revs drop. If bearings or similar were worn, then wouldn't the oil pressure just stay low at temp?

Not to be a bearer of bad luck, but...
Years ago I cracked a centre main cap on my hi-po 1220. Idle pressure was OK but as soon as I revved it, it went south.
I suggest you put a plunger in there instead of the ball, if it still drops pressure with rpm increase it's main bearings or worse, IMO.

ps. These days I prefer the plunger too. The only thing the ball has over it is it won't get jammed with metal swarf, but if you have swarf circulating you have bigger problems.
Author:  Cooper_Matrikon [ Mon Nov 18, 2013 4:42 pm ]
Post subject:  Re: Fluctuating Oil Pressure
So I grabbed a new spring and plunger today, whacked it in and it now build pressure under load (was the opposite). Holds nicely at 50 while its cold then drops when hot. Time for an oil change and hopefully we're back in the game.
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