MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - TD Oilpressure

Hi

My oilpressure has so far been OK - 45-50 with cold engine, approx 40 with warm engine dropping to 20-25 at idling. Last winther I had the engine and gearbox removed to clean and paint everything. No internal work was done on the engine/gearbox.
Now driving the car again, the pressure is down at about 40 with cold engine, dropping to roughly 30 with warm engine and a little below 20 idling.
the engine runs well and I haven't had any problems with it this season at all.
Could it be that the pipe for the oilgauge simply has become dirty or air has foundits way into the pipe causing the gauge to show wrong readings, or should I take this as an indication of something more worrying?
Is there a way to ensure that no air or dirt is in the "pipeline"?
The car has the old vertical oilfilter but has been retrofitted with a spin-on conversion.
As usual thanks in advance

Torben
Torben Olesen

torben, air in that pipe has no effect on the reading on the gauge... a leak in that line would...but your damp, oily foot would give you a clue as to the issue there. a complete blockage would show zero, a partial blockage would only make the gauge slow to react. i understand that what we are really concerned with as we monitor our engines is an unexplained change, but if this were my engine i would not lose any sleep over it...keep an eye on it for any further change and if you are not on an oil analysis program, slice open the spin on filter at your next oil change to check for metal/debris.
just out of curiosity what filter are you using? and i assume the spin on conversion was in place when you noted the earlier readings.
i'm sure others in the group will offer more good info.

regards, tom
tom peterson

Two Questions: 1) What weight oil are you using, 20-50?

2) What was the ambient temperature at the time. With air temp. of 85-90'F. my TF shows a little below 20# also, but the engine is running very hot at those temps.
David Werblow

When did you last change the oil filter, using 20-50 oil?
Len Fanelli

good thought david. torben, where i think david is going with this is since you are looking for reasons why there has been a CHANGE in your oil pressure from last year to this year, did you use a different viscosity oil last summer? was last summer significantly cooler than this summer? regards, tom
tom peterson

Two points in this thread have me thinking. What effect if any does weight of oil have on pressure, if any what would be the difference between 10-30 and 20-50 and what would the pressure change be with a a dirty filter, lower by means of a by pass or higher 2nd to restricted flow
Jon Levine

The rule of thumb, and it works just fine on the XPAG, is that you need 1 psi of pressure for every 100 RPM.

At idle at 700 RPM, 7 psi would be adequate. No one wants to see it that low, but you get the idea.

At high speed cruise, at 4200 RPM, 42 psi would do it.

Anything higher is fine. As it happens, on my TD with 20,000 miles on the rebuild, I have about 65 psi hot under load, and about 25 psi at idle. More pressure than I need, but lower than the 75 psi and 40 psi respectively I started with when the rebuild was new. I use 20W 50 oil.

The book says 40 psi running and 20 psi idling... which is conservative AND based on 30W oil.

Oil pressure is more related to the size of the orifice that it is allowed to escape from, rather than the pump output. You need enough flow to keep the bearings cool by providing the thin layer of oil on which the parts ride, and hence, transfer heat to the oil to be carried away, rather than exclusively to the bearing surfaces. Excessive clearance at bearings both make it more difficult to maintain pressure and cause a larger gap to be filled by the oil, making it less likely that the oil can stay in the gap. The gap in the bearings become the orifice.

Oil pressure is taken off the transfer pipe banjo at the head or the block. The feeling is that the rockers get excessive oil with the size of the orifice used and hence the pressure at the head can read lower than what the lower end of the engine is seeing. The excessive oil was supposed to go down the pushrod openings, but a lot of it was going down the valve guides and coking up the rings and combustion chambers. Eventually, the designers moved the pressure take off point to the lower banjo fitting, and people started to place an orifice at the head banjo to reduce the flow (which increased the pressure at the head slightly as well; which increased the pressure reading at the gauge... but at least now the rocker area wasn't full of oil.

Going to a heavier oil is going to increase the pressure. The engines were designed to run on 30W oil in the summer, but that was about all that was available for motors.

Hope this all makes sense.

Warmly,
dave


Dave Braun

Probably not, but by any chance does your engine have a oil pressure adjuster in it? This would be a adjustable knob where the oil pressure relief spring would normally be.

If so, could it have been changed when you took the motor out? If you do have one, you can also increase the pressure a bit.

MOSS sells these, but not sure how common they are in Denmark.
Bruce Cunha

jon, with the by-pass and regulating ball and spring a dirty filter should not effect pressure readings. as dave mentioned use of a more viscous lubricant will result in a higher pressure reading. regards, tom
tom peterson

Hi

The spin-on conversion was bought from Peter Edney, Essex, UK and the oil used is 30W, since this, as Dave says, is what the engine was built for.
Earlier I have been using 20-50W, but last 2 seasons I've been running 30W, so there is no change from last year to this year regarding oiltype.
I did a quick check this morning, and with completely cold engine the pressure comes up to about 50 at 3500 rpm. Idling just above 10.
Yesterday when I began to worry, was a normal warm day for the season with about 20 degrees C (wonder what that could be in F)and a drive of about 75 km - about 45 miles.
The watertemperature was about 75 degrees C.
Only thing a bit unusually is that there seems to be a small leak where the banjobolt attaches to the top of the oilfilter, but I don't think I'm losing a lot here, and I doubt that it infulences the pressure at all?
I am (of course)leaking slightly when parked, but have decided to wait looking at this until something more serious comes up.


rgds

Torben
Torben Olesen

torben, you are correct..the small seepage you describe at your banjo bolt will not affect your oil pressure. your car appears normal. regards, tom
tom peterson

This thread was discussed between 01/09/2012 and 02/09/2012

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.