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relief valve

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gripper180 robert taylor
essex, UK   GBR
hi all.
my oil pressure gauge runs at 60 psi and was always 40 on tick over. car still runs at 60 but only goes down to 50 and no lower on tick over. tried other gauge but still the same. my question is i assume its the pressure relief valve. can these be serviced or is a new one needed.
thanks bob.

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twentyover Avatar
twentyover Greg Fast
Lives in SoCal, Resides in the Burbs of Detroit MI, USA   USA
Is the second gauge you are using have a different sending unit than the current gauge? My experence with electrical sending units is sketchy

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gripper180 robert taylor
essex, UK   GBR
sorry its a uk car with mechanical gauge. not electric

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chormy Avatar
chormy Gold Member Shaun Holmes
Norwich, Norfolk, UK   GBR
1963 MG MGB MkI "3330 PE"
1964 MG MGB MkI
1967 MG MGB GT "BABE"
1967 MG MGC    & more
Unlikely to be PRV , normally set at around 65-70 psi. , one area thats takes a lot of oil pressure is the rockers if that is getting blocked you can see a lot more pressure.

If you remove the oil filter housing from block you should be able to just push in centre of PRV and release you'll feel the spring/piston grind a bit sometimes.


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gripper180 robert taylor
essex, UK   GBR
hi shaun
gauge in car is showing 60 running 50 tickover, tried another old gauge shows 50 40 tickover still only 10lbs lower. changed flexi hose because it had a kink in it, removed filter housing and relief valve moving ok and changed oil filter, checked tappets for oil as you suggested and oil running out of every tappet. still the same. any other ideas and do you think it is anything to be concerned about.
thanks bob.

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chormy Avatar
chormy Gold Member Shaun Holmes
Norwich, Norfolk, UK   GBR
1963 MG MGB MkI "3330 PE"
1964 MG MGB MkI
1967 MG MGB GT "BABE"
1967 MG MGC    & more
To be honest too have good pressure on both tests two gauges show pressure within the guidelines so for me it's ok
One of my cars is 15psi idle and 40 running at it's fine. The oil pump pushes out 45ltr per 1000 rev so enormous volume.


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gripper180 robert taylor
essex, UK   GBR
thanks for your advice and your time shaun. bob.

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Graham W Graham Walker
Buckingham, Bucks, UK   GBR
My engine has always shown rather high oil pressure, i.e. 70 to 75 psi running at 2500 + rpm.
When hot it drops a bit, to around 60.
When doing an oil change yesterday, I took the valve out and the plunger moved when pressed hard.
I couldn't see anything wrong, so put it all back.
Is there anything to be concerned about?


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chormy Avatar
chormy Gold Member Shaun Holmes
Norwich, Norfolk, UK   GBR
1963 MG MGB MkI "3330 PE"
1964 MG MGB MkI
1967 MG MGB GT "BABE"
1967 MG MGC    & more
Glad yours came out that easy smiling bouncing smiley

If you can do what Robert did change to another gauge or borrow one to go direct onto the block fitting it would confirm your pressures . I think its a bit high reading so suspect the gauge to be a bit off. Other than that I don't see any thing to worry about.

The PRV you will see operate on a cold morning start and rev about 2000 it will go to say 80 and suddenly drop as the PRV comes off its seat. MGB's seem to have a high starting pressure more so than the C. My race C has initial high pressure 85+ but settles at HOT 45-50 @3000 - 7000, idle 15


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mgcbrian Brian Hutchison
Hampshire, UK   GBR
1968 MG MGC
1969 MG MGC
1969 MG MGC ~ For Sale ! ~
Might be interested in my experiences with oil pressure relief valves!! New engine with new valve reading was 80lbs to start then dropped to 70lbs which is far too high. Turned out that the engineering tolerances on the new valves are so fine that when it is fitted in the engine it becomes tight. Replacement fitted, pressure dropped to 55lbs to start and normal running at just over 50 lbs and tick over at around 30 lbs when hot. You can also get it the other way around as well!!

On another occasion had a seized oil pressure relief valve . It destroyed the oil cooler!!!!

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Graham W Graham Walker
Buckingham, Bucks, UK   GBR
Where can you buy new PRV, and are they all the same, or do some run slightly lower than others?

I ran my engine this morning and revved it up to about 2500, but chickened out when the pressure went to over 85.
I did not see any drop-back, so am feeling that the valve is sticking .

Any advice from the group?

Graham

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gripper180 robert taylor
essex, UK   GBR
hi graham,
i know how you feel about chicken out. when i start mine up in cold weather with choke out it can go up to 100 psi, i have to push choke back in pretty quick. my valve pushes in and out under pressure with no feeling of restriction so i don't think its that. if you replace yours please let me know how you get on.

many thanks bob.

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gripper180 robert taylor
essex, UK   GBR
how do you blow out the oilways on the rockers to make sure they are not blocked.

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