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The 100 Forum

oil pressure

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healeysickness Bruce McGauley
London, ON, Canada   CAN
i have been reading about oil pressure and what goes in that oil pressure is still running at 80 psi so i am looking for suggestions. i have checked the oil passages and have removed the oil pan. all looks in order including the pressure relief valve. There is one threaded hole in the centre of the block at the front of the engine justy inside the pan. Am I missing something that goes in that hole?

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Koudekerke, Zeeland, Netherlands   NLD
Can you remember when this high pressure issue started? I had the same problem but found out that it was my own fault.

I blocked the exit of the pressure relief valve with liquid gasket during the installation of the cork gasket. See arrows on the drawing.
Other options are:
• PO installed an extra washer under the relief valve spring to increase the pressure.
• Wrong relief valve spring

DSC03398.JPG    38.2 KB

Dave2526 Dave Deamer
Seal Beach, CA, USA   USA
I had a similar problem with my BN1. After reassembling the engine the oil pressure would be above 80 psi and uncontrolled (roughly linear with engine RPM) after running for a bit. I tried modifying the spring length on the relief valve (just below the oil filter housing ) and replacing both the relief valve and spring to no effect. II removed the relief valve and spring and located the small port behind the relief valve (towards the outside of the block). The small port allows oil bypassing the relief valve to return to the sump to avoid a hydraulic lock from any oil leaking past the relief valve. I fed a small wire brush into the port to eliminate any obstruction in the passage again to no avail. I removed the pan and inspected the notch area in the pan gasket immediately below the small port (between two of the pan bolts). The area appeared clean with only a small amount of gasket adhesive. While uncertain that this was the cause,, I removed the gasket and cleaned all the mating surfaces. I reinstalled with the pan gasket retained with a thin application of silicone on the pan avoiding any application in the area of the gasket notch and no sealer on the block side. This fixed the problem and the oil pressure is now within spec and controlled by the relief valve. While I doubted that the small amount of sealant was restricting the flow, it appears that the relief port flow is affected by small restrictions at the pan to block interface. The valve relief area is only a rectangle the thickness of the pan gasket and perhaps an inch in length . Hope this helps.

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healeysickness Bruce McGauley
London, ON, Canada   CAN
I have checked the pressure relief valve and the sump gasket and all are in order. There should be no problem with oil getting back into the pan.
I did use permatex gasket sealer on both sides of the head gasket and there is some possibility that it could seal off a port between the head/block. Do you think this could lead to the problem of high oil pressure and could this clear in time/use?

Also - any advice on what the 3:8 threaded hole is for in the bottom of the engine -- front centre directly across from the oil pick up pipe in the rear of the engine block?

Dave2526 Dave Deamer
Seal Beach, CA, USA   USA
If the pressure relief valve is functioning properly, any upstream blockage should not affect the oil pressure as the increased flow resistance should result in increased by pass flow. If the head passage is blocked the flow to the rocker shaft or return to the sump should be affected and noticeable with the rocker cover removed.

The only paths I could find for uncontrolled oil pressure were hydraulic lock of the pressure relief valve piston (designated as item 30 oil release valve on page D21 of the shop manual) by any blockage of the small return port on the spring side of the piston, or blockage of the large return line to the sump. I have read some concerns about orientation of the spin on oil filter adapter affecting oil pressure and a sufficient blockage could overwhelm the flow capacity of the return line increasing oil pressure and starving the lubrication system.

The oil flow through the engine is shown on page S/3 in the shop manual although the flow through the small return port is not shaded in green in the right hand illustration but is left to the readers imagination.

My guess for the 3/8 threaded holes is to install a puller to remove the front and rear main bearing caps - at least that's how I used them. The pipe in the rear main bearing cap is a return line from the oil slinger and screw seal .

healeysickness Bruce McGauley
London, ON, Canada   CAN
thanks Dave - I am in the process of installing the spin off oil filter to see if the original is somehow involved. I will then put the pan back on and see what I get. please stay tuned

Dave2526 Dave Deamer
Seal Beach, CA, USA   USA
Based on my results be very sure there is no obstruction (even a smear of gasket adhesive) in the v of the gasket and run a wire brush up the hole in the block between the two sump bolts (after removing the spring and relief valve. I was astounded that cleaning the area fixed my similar oil pressure problem.

healeysickness Bruce McGauley
London, ON, Canada   CAN
I have now checked the relief valve port and it is clear. Also the gasket is trimmed well back of the port. The spring is strong - it is all I can do to push the cap/bolt on to get the thread started and then screw the bolt in. I installed the adapter oil filter and a new Fram oil filter in case the problem was with the original filter. The pan was reinstalled using the old gasket and all the bolts snugged up. I started the engine and no leaks. I went for a 4 mile ride and the oil is still at 80 psi when driving. It drops to 60 during idle but as soon as I hit the gas it goes up to 80. Any suggestions/advice would be appreciated. thanks

RTaillieu Avatar
RTaillieu Rick Taillieu
Leamington, ON, Canada   CAN

If the spring is too stiff it won't allow the bypass to open to lower the oil pressure.
Have you talked to Bob or Tom at Autofarm about this?
Have you confirmed that you have the correct release valve and spring installed, someone may have put in different parts at one time to try to fix low pressure?
I'd try to source a different spring and try that first,

'64 BJ8 P1
'69 E-Type 2+2

Koudekerke, Zeeland, Netherlands   NLD
I agree with Rick, must be the valve or the spring.

Did your car had always this high oil pressure or when did this started.

rusty1c Avatar
rusty1c Peter D
Antioch, CA, USA   USA
1961 Austin-Healey 3000 BT7 "RUBY"
1963 Chevrolet C10 "Rusty"
Is it possible that a high volume oil pump has been installed thus pumping more oil than the relief valve can handle? This would also cause an increase in oil pressure.

healeysickness Bruce McGauley
London, ON, Canada   CAN
thanks all for your responses. The engine was rebuilt recently and the original oil pump was used. I will get another pressure valve spring to see if that helps. The one I have is quite stiff and requires all my thumb strength to push the retaining bolt on. Can anyone verify that it should be this stiff or should it be a weaker spring?

Wilbert Avatar
Wilbert Wilbert Peters
Smilde, Netherlands   NLD
1954 Austin-Healey 100 "Cobra Nose"
1955 Austin-Healey 100
Find an old original spring used for the 100, most new springs a used had the same problem. There is a difference between the springs for the 100 and the later 3000

gramos Avatar
gramos Graham Foster
Kefalonia, Greece   GRC
I have been reading this thread with great interest as I am now in the same situation as Bruce .
I have just rebuilt my 100 engine and am getting 100 + psi on the oil pressure gauge !

It has only run for a few second bursts as I don,t want to damage anything .
So far , this week , I have tried putting the old spring and bullet back , checked the oil feed pipe from the block to the gauge ,
and there is certainly not 100 psi coming out of the block/ pipe union , it looks quite normal , another , new filter fitted , rockers are getting well fed with oil .

oil pump was rebuilt to the factory clearances , all oilways thoroughly wired and cleaned ,
gasket was cut to clear the oil drain hole from relief valve ,

So I am at the brick wall with this ,
only thing that comes to mind is that , for some reason the gauge has developed a fault ?
when bleeding the oil pipe to gauge the flow is normal , not 100 psi !
prior to rebuilding it showed the usual pressure .

Reason for the rebuild was a badly worn cam lobe on no. 1 inlet valve , oh and the last time the engine was out was in 1989 !!

the engine starts well and sounds sweet , I would welcome any more suggestions , please ?

Vintage n Classic Avatar
Vintage n Classic Silver Member Geoff Golding
Nelson, Tasman, New Zealand   NZL
I have been advised; sometimes these type of problems are via the relief valve sticking/being caught in the chamber in which it operates. The relief valve gets stuck on a wear groove. The groove is caused by wear over now 60 years use. During a rebuild this area is generally overlooked other than just flushing it out to make sure its clean.

Solution is to chamfer the square edges off the open end of the relief valve so they become rounded rather than square. This then allows the relief valve to ride up and over the wear groove in the chamber and move freely, thus giving correct oil pressure.


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