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MG TD TF 1500 - Oil pressure

Having just reclaimed my 1950 TD from 14 years of inactivity, I'm curious as to what the running oil pressure should read . It maintains 60PSI over 1500-2000 RPM and beyond. At idle when warm, hovers around 20PSI. What should the pressure read in a healthy XPAG?
John Pflugi

That is good. Depending on how hot your car runs. 40 lbs is acceptable at running speeds when hot, 60 when cold. If you are getting 60lbs when hot then thats good too.

Chris
Chris Couper

My 50 TD runs at no more than 15 - 20 psi, and briefly at 25 max when cold. However, looking through the oil filler cap on the valve cover, oil seems to be splashing all around. Is this a good enough indication that all is well?

Steve Markman
R Markman

If you are only getting 15-20 and 25 cold I would suspect it is time for new bearings. You could also check the oil pump and a number of other areas to look into.

Chris
Chris Couper

Steve, My oil pressure gauge read slightly lower when it came back from rebuilding and re-printing. It could be that your pressure is fine but the gauge is giving a lower reading and may need some attention. You could perhaps get a garage to connect an external OP meter to check out the actual pressure before thinking about new bearings. AB
Adrian Bennett

Many times I have seen that the oil line from the block to the cylinder head has been installed wrong.The oil pressure take off to the guage should be installed so that the flex line connects at the bottom. Also if there is an awful lot of oil splashing around in the valve cover , it could be a sign of badly worn rocker shaft and bushings.
Sandy Sanders
conrad sanders

You need 10psi/1000 rpm to keep metal off of metal. Buy a cheap pressure gauge at a parts store and plumb into the banjo bolt entering the block. That will give you accurate pressure in the main galley. Get an extra large banjo bolt, drill, tap, and thread the needed adaptor to do this. I ran into this with a friend's TD with recently rebuilt motor-all was fine, except the bad oil leak. We pulled the motor, fixed the leak, and had very low oil pressure. Eventually figured out someone had soldered one small banjo bolt nearly shut (to the head) to restrict flow/raise pressure. When we reassembled, we put that bolt on the bottom and the gauge then read the restricted pressure to the head, etc. George
George Butz

What is the max pressure you should run at, I have an adjustable relief valve and see over 60 If I am at 60 MPH.
Tatty

The oil flex line installed at the head rather than the bottom is not "wrong" as a previous post suggests. That's the way it was done on the early TDs. Check an early TD shop manual and look at the pictures. However, by moving the pressure gauge take-off to the lower position WILL show an increase in indicated pressure. The pressure doesn't really increase, only the INDICATED pressure changes.

45 PSI (with take-off at the bottom) is plenty for a fresh engine. Volume of oil flow is more important than pressure. In fact, too high a pressure is no more healthy than too little. If the pressure is too high it can lead to premature wear on both the oil pump driving gear as well as "worm-holeing" on the bearings. All that is necessary is to have enough flow of oil to get between the crankshaft journals and their respective bearings. Once there, the oil will be distributed around the bearing and set up an oil film.

In short, 25 PSI warm is sufficient, 45 PSI warm is excellent, 60 PSI warm is likely too much unless you have a fresh engine and are into racing the car.

Cheers,
Lew Palmer
Lew Palmer

C Sander is correct that coming off the bottom will increase the oil pressure by as much as 20 lb. Seen it happen several times. It may not be necessary to change but it changes the pressure. Another thing that lowers the pressure is the hole feeding the oil to the rocker arm. It is the size of a pencil and it only needs to be a small hole that gives a small amount of oil to the rocker arm shaft. I put a restrictor made of very thin copper and it furnishes enough oil without slinging it out every where. This info is not my original; came from a mechanic who has worked and rebuilt Jags and MGs and other cars all his prof life. C Sanders is a noted rebuilder of MGs also.
Ellis
Ellis Carlton

Cheers Lew
Tatty

John and Lew
The subject of where to connect the oil line to the oil pressure gauge at the engine block has been discussed many times on this site. If you look at “The MG midget (Series TD and Series TF) Workshop Manual” on pages A.4 Fig. A.1 and page A.29 fig. A.35 you will clearly see that the connection for the oil gauge is located on the bottom of the engine. Also refer to the page A.30 and you will see that the oil gauge is not connected on the top, by the head. Oil pressure readings taken on top by the head will read less oil pressure than those taken at the bottom, by the oil pump and filter. If you read the text in this section you will read that if your oil pressure goes above a reading of 50 to 70 lbs. per sq. in. that the by- pass will open. I take this to mean that you are now bypassing the oil filter and pumping unfiltered oil into the bearings and camshaft. The purpose of the by-pass, as I understand it, is to give the lower bearings oil when the filter is dirty and clogged. This lets you save the lower end and sacrifice the upper engine. This section also states that the normal working pressure of the engine is 40 to 45 psi. So I believe Lew is correct, too much oil pressure is not good either. But over all Conrad is correct, according to the workshop manual. Hope this helps
John
John C. Hambleton III

There are two "bypass" valves- in all late and early cars. #1 is in the outer pump cover, and regulates pressure only, and has nothing to do with bypassing the filter (it causes an internal pressure leak in the pump). Early (external)filter cars have the "clogged filter" bypass valve (#2) in the block just inside the pump, and later (horiz. filter) cars in the filter, plus the filter itself in held in place by a spring which would allow leakage if badly plugged. George
George Butz

George
You get a wee thank you from me too. Thanks for straighting me out on that. When these by passes open where does the oil go. Does it go back in the sump or does it go up the oil passages? I think in my first TD it went on the garage floor thru that little hole , with the carter pin in it at the bottom of the bell housing. The reason I thought it was by passing the filter, was the floor was so black. Thanks again for the help. John
John C. Hambleton III

<<<snip>>>
When these by passes open where does the oil go. Does it go back in the sump or does it go up the oil passages?
<<<Snip>>>
When the pressure relief valve opens the oil goes back into the inlet side (suction) of the oil pump.

When the oil filter bypass opens, it does just that. The oil bypasses the filter and goes into the the main oil gallery unfiltered. Look at pages A.8, A.9 and A.31 in the TD workshop manual.

<<<snip>>>
I think in my first TD it went on the garage floor thru that little hole , with the carter pin in it at the bottom of the bell housing. The reason I thought it was by passing the filter, was the floor was so black.
<<<snip>>>
That's oil escaping from the rear main "seal" which isn't a seal, but a reverse scroll and oil slinger. Look at pages A.22, A.23 and A.31 in the Workshop manual.
Bullwinkle

Oil pressure has been just one of those things I learned to worry about after I got my 50 TD last fall. I have an early printing of the owners manual and on page 14 it states that the normal operating pressure is 60 lb (4.2 kg); however a later version of the manual same page says 40 lb (2.8 kg). My 1950 workshop manual for home cars doesn't refer to an oil pressure range on page A5 but the supplement says 40-45 lb. The picture on page A2 shows the pressure take off from the head while the fig A1 page A4 shows the pressure take off from the block.
When cold my car shows 55 lb at 2000 + rpm and when warm around 40 and if it should idle way down it drops to 20. The take off is from the block, the gauge is probably 50 years old and who knows just how accurate -- so I like to think it is all directionally correct and if I see any big variation from these ranges then I'll panic.
I think Neil Cairns says something about too much attention being given to precise oil pressure readings.
Dennis
D F Sexton


I have a late 1953 MGTD and rebuilt the head and replaced all the lifters . The car runs well and I have good oil presure ( 40-60 lbs ).
My problem is that when I start the car after sitting a few days the oil guage sits a -0- for about five seconds then pops up to normal.
I took off the oil filter after the car had been sitting for a few days and there was about a spoon full of oil in it . There are no leaks outside the filter . How is the oil getting out ? Should I worry ?
Alan

AFAIK there's no anti drain back valve. So, indeed the oil in the filter can drain back into the sump. If you're really concerned and have a good battery, crank the engine until you see oil pressure before turning on the ignition. Frankly, I just start it up and keep the revs down until the pressure comes up.
Bullwinkle

Bullwinkle, thanks for your reply on the oil presure , or the lack of it . I spoke to Bob at Abingdon Spares he told me to look at the ball check on the oil presure regulator . I did,,, it had as he suspected a nasty grove in it . I replaced the ball and spring and presto the problem went away at a cost of about $4.00.
Thats my kind of fix. On top of that I now have better oil presure to boot.
alan

Chaps, I just noticed in my TF1250 handbook (reprint of original) that it says oil pressure should be in the range 25 - 40 psi, with the lower figure at lower engine speeds. So why did they calibrate the gauge all the way to 100psi? Many people over the years must have had sleepless nights because the needle stays in the bottom half of the gauge ............ AB
Adrian Bennett

"...pressure in the region of 40 to 45 psi. at normal running speeds." As previously stated by Lew & others this is of course correct, as per WSM pg.8. The statement below this i find intresting & humorous, "So long as it is showing a reasonable pressure it may be taken that the circulating system is working satisfactorily". Also opperating temp. of OIL is only achived AFTER coolant temp. reaches its normal temp.(15 minutes or so at highway speed, on a hot day) Len
Len Fanelli

With all this talk of oil pressure no one has mentioned what weight oil they are using. This can have an effect on pressure, right?

I was using straight 30 weight and then changed to 20-50 and experienced much better oil pressures.

What is the recommended oil?

David
David

My XPAG engine was completaly remade. Since 3 years I drove 4500 kms. I use syntetic oil 50/10.
When the engine is cold the pressure shows 80 psi and after some miles the indication is around 60. At idle speed the indication is 25.
For me it seems normal with a new engine. What do you think?
Georgibus

Georgibus:

Seems high but who knows if your gauge is correct.

Chris
Chris Couper

My XPAG runs 80 PSI on a cool day at startup. 45-60 PSI depending on hot the day is, and 20-25 at idle using 20W50. There didn't seem to be much change for very hot days when going from the 10W40 to the 20W50.
Bullwinkle

This thread was discussed between 28/07/2003 and 25/08/2003

MG TD TF 1500 index

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