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Loss of oil pressure


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Whilst cruising at about 70 on the A34 en route to Malvern, noticed the OP gauge needle moving steadily left wards so pulled off and coasted into the nearest village. Bonnet up and no obvious signs of oil being expelled. Tentatively moved off but could only keep pressure up close to 50 by high revs in each gear. Normally idles around 30 and sits at 55/65 at speed. I then had to accelerate pretty sharply from standing to get across a junction and suddenly normal service resumed. Stayed that way to Malvern and on a glorious cross country run towards home (Tewksbury > Stow in the Wold > Lechlade > Wantage - try it some time).

 

So I am thinking a bit of crud somewhere and an early oil change but any other possible explanations, things to check?

 

Miles

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I have now a similar problem which is bizarrely intermittent. Start the car and have 70-75 psi let it idle when warmed and drops to to 50-55psi. Sitting in traffic waiting to exit the Biggar Show on Sunday and pressure sitting 50 psi with engine hot and fan running.

 

The engine has only done around 500 miles and is due an oil and filter change so hoping it is the bedding in **** that intermittently gets between the ball and seat.

 

Is it possible to get the valve body as I have already changed the ball and spring due to decayed chrome which caused real issues on initial running. Can the seat be lapped in any way to clean it up?

 

There are no ominous rumbles or rattles so I suspect the problem is not main bearings and I do not have any reason to suspect the oil pump either by the way the pressure comes up quickly and cleanly from start up.

 

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Rod

 

Sounds as though it might be wise to remove the whole assembly from the block and clean it out very carefully. You can remove the pressure release valve assembly by undoing the bigger nut, but there are little nooks and crannies around it that might be better for a bath and brush up.

 

Ash

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Hi Alan, I have seen this oil pressure worry once now, car has done 12000 miles since full engine rebuild, no other noises or oil leaks, oil pressure has always been excellent. I will remove my oil pressure valve and inspect/clean. What bearing details did you give simply bearings ltd so I can quote/reference sizes etc for ease of order?

Many thanks, James.

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Here's a minority opinion: Admittedly, most of my experience with these engines came from a time before they had the opportunity to accumulate 50+ years of crud in the relief valve or anywhere else, but from that time, at least, I don't ever recall a releif valve causing a low pressure problem.

For what it's worth, the first thing that comes to my mind is crud in the line to the gauge or a fault in the gauge itself.

Tom

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After an engine rebuild on my 3 back in the late 80s, I was plagued for several weeks with 'OP needle swinging to the left' syndrome, accompanied by low but not zero, oil pressure.

In every case I found a small bit of carbon/sludge or broken piston ring causing the relief valve ball not to seat against the spring. Lord knows how I'd missed the debris during rebuild, but we can assume fragments were concealed in the oilways, and I'd not looked closely enough.

I resorted to keeping the relevant sized spanners in the cockpit and became a dab-hand at extracting the valve and liberating the unwanted residue, by the roadside. Eventually I dropped the sump and scoured it - and either that, or an exhausted supply of crud, seemed to cure the problem.

It sounds as if something similar to my experience could be the cause of at least one of the complaints here. Irregular balls, though - that's an interesting new one in the equation...

Tim.

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  • 3 weeks later...

Sorry for the late catch up on this one but I have been travelling.

 

Thanks for the additional input and further suggestions and information. I am replacing the spring and ball as a precaution (noting the observations re irregular balls) but will also drop and clean the sump once the weather deteriorates.

 

Miles

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Sorry for the late catch up on this one but I have been travelling.

 

Thanks for the additional input and further suggestions and information. I am replacing the spring and ball as a precaution (noting the observations re irregular balls) but will also drop and clean the sump once the weather deteriorates.

 

Miles

Hi Miles

 

Good to meet you at Malvern

 

Hope you enjoyed you first IWE.

 

Cheers

Guy

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Likewise Guy.

 

As an IWE virgin I really enjoyed the event and particularly the Forum meet - names to faces and all that. Met someone who knows who rebuilt my 3A originally (but still trying to make contact).

 

So diary permitting I intend to make it to Harrogate.

 

Miles

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Miles

So was that you parked opposite the Land Rover? if so should have come over for a beer :) I was busy at the forum meet helping someone out ;) Guy should have introduced us :wacko:

Neil,

 

Yes that was Miles opposite.

 

And yes i did introduce Miles to as many peeps as i could, including your good self.

 

Too many reds my friend.

 

"Thats a nice one , oh ok i will have another" ( me not you) and so it went on.

 

Cheers

Guy

Edited by Jersey Royal
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  • 10 months later...

Belated update on the original problem.

 

Pre CLM trip sump dropped and cleaned (no obvious bits). OPV unit removed and cleaned. Spring and ball replaced. Interesting flat in the spring about 1/4" long. New filter. Also had a plug with a 1/8" hole removed from where the crancase breather pipe would have been and a refurbished breather installed. Then set the pressure to about 65 psi at 2k revs. Travelling in France with changing road conditions (we took cross country routes), generally all fine. Pressure sitting at about 70 - 75 psi at higher revs. However, 15 or more minutes at sustained speed on N route and pressure started to drop to sub-50.

 

So the gremlin is still there I think.

 

Next task will be to clean out the line to the gauage and perhaps a replacement gauge (faulty gauge got the popular vote).

 

Will report back (probably next year!).

 

Miles

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Ash

 

For what it is worth the oil pressure levels are my fault.

 

After the work described above a couple of weeks ago, the oil pressure was even lower. Conventional wisdom here was that it should be around 70psi at 2k revs and around 80/85 at higher revs. Adjusting the oil pressure relief valve it settled at 90+ psi at higher revs; a little too high. Adjusting it downwards in a carpark before getting on the ferry for the weekend after the run to Portsmouth was not ideal and I obviously slightly over-reduced the pressure. Tricky getting it right by oneself and one needs a good blast to see what the real running pressures are.

 

Resigned to finding decent engineers in Surrey to sort it all out now though...

 

Miles

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