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MG TD TF 1500 - Oil pressure high

Because the oil gauge shows 100..120 psi I wanted to known the reason - bad gauge or real high pressure.

After measuring with an external manometer now it is clear that the pressure is (too?) high.

Therefore I want to understand the direction of oil flow around the oil pump.

Is there a scheme/diagram which shows how or where bypass valve and relief valve are designed into the flow?
Bela

https://www.youtube.com/watch?v=ShHAaDKL3gM&list=PLmh229uhw0-cAYqoag9KAfa-NAdiq7iWq&index=20

will give you a bit of a clue.
mog

Bela,
if you have a separate filter fed by pipes the filter bypass is in the block. If you have an integral filter (late TD) then the filter bypass is in the end of the pump body under a plate.
A high pressure normally indicates the relief valve spring is incorrect or a spacer has been fitted. Fig A36 page A31 in the manual.
The relief valve is in the same place on both types of pump
Ray TF 2884
Ray Lee raybar2(at) tiscalidotcodotuk

Thanks all for the hints!

The car is an early TD and has a separate filter. This filter has been substitute by a modern filter.

The pre owner add an valve in the sump. He didn't want to wait for pressure.

But why isn't the by-pass valve in action?

Is the drawing right?

Bela

Not quite right Bela.
The oil pressure relief valve opens to let the pressure side bleed into the pump suction side controlling the pressure.
The filter by-pass valve opens to send the oil directly into the oil gallery in the block if the filter blocks.
If the filter blocks there is no indication as the oil just takes another route.
The oil pressure is governed only by the relief valve and engine clearances.
If your oil pressure connection is at the cylinder head check that the lower banjo bolt does not have a restrictor fitted ( some were modified to give an better idea of the true oil pressure).This would reduce the oil flow to the engine but give a high reading.
One after market filter assembly was ported the wrong way and the anti drain back valves in the filter canisters restricted the flow and gave high pressure readings.The oil flow must be from the outer to the centre to lift the valve diaphragm.
Hope this helps.
Ray TF 2884
Ray Lee raybar2(at) tiscalidotcodotuk

Hi Ray

thanks - the most I'd understand. It really helps. I could hear some pennies fall down.

You wrote:

anti drain back valves in the filter canisters restricted the flow and gave high pressure readings.

Must in that case the high pressure only exists in front of the restriction?

How can I determine such restrictor - is a picture available?

Does my diagram now hit the reality?

Bela

sorry Bela,
I made a mistake, the restrictor is not in the oil supply line. I have a TF and forgot that the TD oil supply goes into another tapping in the block.So the restrictor has no effect on the oil pressure.
If you remove your oil filter canister and turn the engine with the starter the oil should not come out of the nipple that the canister screws on to.If it does, look in the small holes in the canister, if there is a rubber sheet inside covering them than that is your problem.
If this is the problem then your oil is by-passing the filter straight into the engine.
If that is OK then the fault is with the oil pressure relief valve. It may have a wrong spring, there is an earlier post about this.
Ray TF 2884
Ray Lee raybar2(at) tiscalidotcodotuk

Thanks again Ray,

I have to investigate.
Bela

The more I look the more I confuse myself!.
The oil pressure gauge is the last item in the system,any restriction before that will show a lower pressure not higher.
High pressure can only come from incorrect spring in the relief valve.Anything else would open the filter by-pass valve and dump to the oil gallery.The pressure gauge would then read the gallery pressure which would be lower.
I think!
Ray TF 2884
Ray Lee raybar2(at) tiscalidotcodotuk

Double springs in the relief valve were the culprit.

Taking off the additional smaller spring returns to a normal oil pressure.
Bela

Glad you got it fixed...and figured out.

Think you could do another drawing if the system, similar to the above, for our reference...those were easy to follow.

Thanks,
Gene
Gene Gillam

Hi Gene,

the picture uses common hydraulic symbols - I don't know an alternative to show the function of valves and pump.

Bela

Bela-
Did your springs look like these? "Oil pressure booster spring" BMC part #706/226. AKA the "60/80 spring."

I found it added 20 psi, or a high of 80 down to 60 when removed.

D mckellar

This thread was discussed between 15/04/2016 and 27/06/2016

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