Lotus Elan

abnormally high oil pressure

PostPost by: lotusfour » Tue Sep 10, 2019 5:20 pm

This is a newly started engine in an S4 that I acquired as a 'stalled project'. The gauge reading at start up and at operating temperature idling is between the 60 and 100 . I have needed to sort out numerous issues with the car, the history is a bit cloudy. I do know that the po had the head done. I had the engine and gearbox out to replace the rear gearbox oil seal. At first start up I could not build oil pressure so I used the vaseline in the oil pump method. Could some vaseline have gotten plugged up somewhere? There is a small oil leak at the gauge fitting, so it seems that high pressure is forcing out a small amount. Another thread I read suggested the pressure relief valve in the pump. Would the pump need to come out to inspect and what would I be looking for?
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PostPost by: 2cams70 » Wed Sep 11, 2019 12:07 am

Especially if the engine has been sitting check for a stuck oil pump pressure relief valve. The clearances between the plunger and it's bore are tight. Light corrosion or carbon gum can cause it to seize up.
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PostPost by: Chrispy » Wed Sep 11, 2019 1:05 am

Do you trust the gauge? Mine was reading very high and turns out it had the wrong sender.
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PostPost by: StressCraxx » Wed Sep 11, 2019 2:17 am

Warm the engine until the oil is at least 150F. Take it out for a drive is best.

Remove the sender/fitting and install a known good pressure gauge. Start the engine and check. Should be 35 to 40 PSIG on 20W-50 oil at 3000 rpm. You may see 60+ PSIG with cold oil. Oil pressure at idle 10-25 PSIG.
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PostPost by: 1owner69Elan » Wed Sep 11, 2019 6:44 am

As you apparently don’t know what may have been done by the po, are you sure you don’t have a high pressure oil pump fitted? The fact that you have an oil pressure gauge that reads above 60 lbs (not stock on an S4) suggests further that perhaps the po may have gone with a high pressure pump.

My car has a high pressure pump and my stock gauge is pegged at 60 lbs. The engine builder fitted this pump for a high spec engine. I have been trying to get Caerbont (Smiths) to supply me with a 0-100 psi dual gauge, that they have promised to customize (customise) in the correct S4/Sprint font, for 2 years. Still waiting.
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PostPost by: vxah » Wed Sep 11, 2019 7:23 am

I'm not sure I would be taking it for a run if the pressure really is that high! Might be a good idea to find another gauge just to verify accuracy? Did the po fit a new oil pump? As said, the relief valve is known to stick and when looking inside the pump body it's not clear what part should move. I bought a new old stock ford pump and it looked perfect but, the relief valve was stuck! (I checked before fitting thanks to this forum)
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PostPost by: lotusfour » Wed Sep 11, 2019 1:42 pm

Thanks for the replies. The pressure goes immediately to between the 60 and 110 markings and remains there, no movement. The car has been a 'project' for a number of years. the po had not driven much more than 'around the block' a time or 2. In the file of info there is documentation from the owner previous to the po about an engine rebuild which included an oil pump. No notes as to it being high pressure. Is a high pressure pump externally the same in appearance? The cover is held on with 3 socket head cap screws rather than bolts, which may mean nothing. I am tending to believe the gauge as correct as it is weeping oil even though the fitting is tight. I had hoped a member has had similar issues and found the cure. A thread by daverubberduck sounds exactly the same, pressure around 80. I read a thread on the Lotus 7 forum which sounded exactly as my issue and it was a stuck valve. Being in Canada with no parts source in country, I am leaning towards ordering a pump from Burton and just bolt it on when I remove the current one.
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PostPost by: vxah » Wed Sep 11, 2019 3:12 pm

You don't need to take the thing to bits to check the valve. Take it off the block and have a look from the back side.. you will see a spring retainer pressed in holding the end of the relief spring, look at the other end where that spring goes into the housing and you should see the plunger? See if you can find a suitable tool to push the plunger off it's seat? It should move with a bit of leverage..
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PostPost by: Craven » Wed Sep 11, 2019 3:20 pm

Using a tyre inflated to a known pressure it’s not that difficult to arrange a connection to the gauge in the car, I do it from the engine end, to check a couple of points on the dial for accuracy.
High pressure pumps look externally the same as usually they just have the internal relief valve pressure increased.
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PostPost by: oldelanman » Wed Sep 11, 2019 3:26 pm

lotusfour wrote:I am tending to believe the gauge as correct as it is weeping oil even though the fitting is tight.


Check that the small sealing washer in the pipe end fitting is present and not damaged. They can fall out when fumbling behind the dash to fit the gauge line.

If your oil pressure has significantly exceeded 60 psi it's possible the gauge may be damaged and may need recalibrating .. does the needle return to zero? My newly refurbished gauge was wrecked when my pressure relief valve jammed shut .. hopefully yours is OK.
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PostPost by: denicholls2 » Thu Sep 12, 2019 12:09 pm

Jamming of the relief plunger usually results in higher pressures than 60-110 -- on my BMW 1600, it caused the O-ring in the oil filter to pop.

As a reference, 85 psi is normal pressure for the Europa-Renault. So although the Twincam by design runs a much lower pressure, you're not in the destructive range. Almost all of the pressurized oil pathway is metal-to-metal.

I too suspect a high-pressure pump rather than a defect.
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PostPost by: 2cams70 » Thu Sep 12, 2019 2:37 pm

Yes you are in the destructive range if that's your actual oil pressure. Do what others have suggested and connect up a test gauge to validate your instrument panel reading as a first step. I've known the standard oil filters to split at excessively high pressures.
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PostPost by: lotusfour » Thu Sep 12, 2019 4:04 pm

I have a spare gauge so testing the pressure with it will be the next step. If it ends up I have to remove the oil pump, how do i determine if it a high pressure or regular valve?
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PostPost by: mbell » Thu Sep 12, 2019 5:31 pm

I think the high pressure pumps often have a much thicker end plate.

Rdent.com has a photo of both types they sell.
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PostPost by: nmauduit » Thu Sep 12, 2019 6:34 pm

mbell wrote:I think the high pressure pumps often have a much thicker end plate.

Rdent.com has a photo of both types they sell.


no, I think the thick plate pumps are the high volume version (wider rotary elements pumping more per rotation), the pressure is set by the spring of the valve (stronger spring = high pressure).

nb: if the engine is worn out, or the oil very thin, the pump may not raise the pressure to the valve stabilized level at tick over - yet the 2 rather independant settings mentionned above still apply.
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