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MG TD TF 1500 - High oil pressure

TD29330 fine for 18 months, changed oil & filter Nov 2015. holds at 40psi up to 4000rpm, up to 45psi when occasionally faster.
noticed oil pressure down to almost zero, found 'plug' bolt on top loosened by approx 1/4 inch. (see diagram, big red arrow).
tightened plug and primed pump, now get 80-90psi !
before I start, does any of you wonderful people have any insight as to what has happened?

M Lees

When your plug unscrewed it uncovered a drillway into the filter housing , just above the filter bypass drillway. This hole is to allow air to escape when you prime the filter housing.
In yours it let the oil bypass the filter bypass valve and enter the oil gallery at a different place.
I haven't worked it out yet, but it looks as though it also shunted the pump flow to the suction. I need to take my pump apart to see all the drillways and what they do.
Ray TF 2884
Ray Lee raybar2(at) tiscalidotcodotuk

Thank Ray, I look forward to hearing from you again.
M Lees

My suspician is the relief valve directly below that plug.
I'd remove the prime plug and relief to see to if something is blocking the relief. The ball and spring ought to drop out, or, if not, you might find (don't have a pump end plate to examine) it is a direct shot between the primer hole and relief, and drive the ball out with some sort of rod if the ball is stuck.
JRN JIM

Can this be done without draining the oil?
M Lees

Jim.
it is not the relief valve plug but the priming plug next to the filter body.
M Lees. I have got my spare pump off and will follow all the passages and see how they all interconnect.
I have realised that the filter bypass port goes into the same point as the main flow. That is on the later filter, on the early (TC TD) they go in different points.
Good brain exercise for me as for once I have nothing to do on my TF.
Ray
Ray Lee raybar2(at) tiscalidotcodotuk

just had a good look at the oil flow route through the pump. The displaced plug could not alter the pressure as it would only bypass the filter.
I think that something was under the pressure relief valve ball and has now been flushed away.
Another possibility is that the ball has ring seated and had turned and is now back in place.
Under the pump is a large brass plug retaining the relief valve. Unscrew this and out will come a spring loaded ball and guide ( note the order) if the ball is marked in any way fit a new one.
A friends car suddenly dropped its oil pressure and we found a wear ring around the ball, fitting a new one gained 15 psi at the gauge.
You don't have to drop the oil.
Ray
Ray Lee raybar2(at) tiscalidotcodotuk

Maybe it is the wrong bolt/plug and is too long, and tightening blocks the relief valve channel or mechanism? Been years since looked at a later type pump but just a thought. George
George Butz

Ray. I'll look at the relief valve and see what I find.
George. Worked fine fully in for over 12 months, so must be right length
M Lees

Mike, Peter from our group. My TD runs at 70psi at all revs from 1K upwards and ticks over hot at 25psi. I have always been a little concerned about the higher pressure (why worry about a good thing?) I notice on the net that Peter Edney is offering and adjustable pressure relief arrangement for not an inconsiderable sum of £65. That suggests to me that this is a historic issue with Xpags, perhaps?
P J Wilgoss

Removed relief plug etc, found ball had ridge, new one ordered.
After much research, found this; same pump,

http://www.mgccyregister.co.uk/technical-information/the-xpag-files/engine/the-xpag-oil-system/

I will look at the pump bypass valve, behind the filter plate to see if all OK. Does anyone have a diagram of this parts internals?
M Lees

The valve body is brass. I tried to remove mine once and all I did was chew it up. I think it is a sealed unit and no longer available.
It only has to handle the oil filter differential pressure. If the filter is good then it does not do anything.
As to oil pressures.
mine is:-
75 cold at 3000rpm 30 at tickover.
50 hot at 3000rpm 10/15 tickover.
and has been for many years. I don't hang about ( 70 mph cruise with 3.9 diff) and it has never changed.
The main opinion is that 10+ PSI per 1000 revs is to be aimed for. It is oil flow not pressure that matters.
I was always taught that when all the needles were at midpoint then all was OK, so my TF should be alright for a bit.
Ray TF 2884
Ray Lee raybar2(at) tiscalidotcodotuk

Thanks for the various assistance regarding my high oil pressure.

I removed the oil pressure spring and ball – found ball to have a groove – perhaps it was sticking?

Replaced spring and ball, also oil filter.

Now getting 50-55psi cold, 40-45psi hot, 30psi idle – happy days..
M Lees

spring pressure valves have a peculiar habit.
If there is any flow ( ie a groove allowing flow ) the down stream pressure is lower tending to lift off the valve.
Still don't know what caused the overpressure but glad it is sorted
Ray TF 2884
Ray Lee raybar2(at) tiscalidotcodotuk

Many thanks Ray for all the info, especially stopping me potentially wrecking the bypass valve. What a great site.
M Lees

This thread was discussed between 14/07/2016 and 21/07/2016

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