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MG MGA - Oil pressure

This may be a previously covered topic?

Pushrod engine had a spate of overheating and a cracked cylinder head.

Replacement head and composite gasket along with new thermostat; cooling is now OK with new coolant and engine oil plus filter.

Oil pressure used to be in the 40-60 psi mark. However, now, after 25 miles, oil pressure dropped away (circa 15psi) whilst underway. Using Dynalite 20/60 oil. When the engine is cold, pressure is back again but then drops off.
Also appears to have some mist spray under the bonnet that can't trace to a source.

All opinions welcome.

regards
Colin
Colin Manley

With overheating and a cracked head there would be a good chance of getting water into the oil.
This could cause significant bearing damage..
I suggest an examination of the conrod and main bearings.

Is the mist an oil or water mist?

Mick
M F Anderson

Colin. Have you recently changed to a spin-on oil filter or replaced an old style filter? I missed removing the gasket and put a new one on top of the old. This caused a mist after a few miles and then the gasket blew, dumping all the oil on the road.

Steve
Steve Gyles

It's not my car, and I haven't got sight of the engine directly.

The filter has always been a spin-on and the old filter retained the seal upon removal so all is ok. Filter is tight and dry at the seal face.

Photo shows (just about) the oil splatter, but no obvious leaking point and the flexible hose is ok.


Colin Manley

If you run it without the dip stick, it will spatter oil out through the dip stick tube.
barneymg

I would not drive an MGA that has 15 PSI of oil pressure at road speeds.
An urgent check of the conrod and main bearings, the spring of the pressure relief valve, the oil pump, and the pressure gauge instrument should be carried out.
If it is a bearing problem you can expect a conrod to appear out the side of the block any time soon.

Mick
M F Anderson

Colin
with the bonnet up,can you rev the motor and see if you can locate the source of the spray?
I did this once and I found that if I held a sheet of white paper in the region of the oil spray, I could see where it was coming from much easier.

Colyn
Colyn Firth

Good idea about the white paper and, only this morning, I thought about the pressure relief spring.

Apparently running hot still does occur on a motorway, so I do wonder if the Radiator may be not working efficiently when the engine is under constant load (it does not seem to get hot on local roads) and the heat is making the oil too thin.

Anyone know a proper radiator shop that would re-core the original rad (I know new replacements aren't up to full spec).

It is difficult trying to analyse two apparently different, but possibly interrelated, conditions.

regards
Colin
Colin Manley

Colin

I believe Bob West will turn round the radiator in about 2 weeks.

Steve
Steve Gyles

Colin
Steve is right about Bob West for a radiator BUT the radiator is not the cause of a drop to 15psi. I don't know answer without seeing car but one comment is it appears the mist is showing up on the RH side of the engine as it may dismiss some LH side causes. I suppose if relief valve is stuck open or spring broken, it could cause big drop but I have never heard of it and that spring is very strong. Unfortunately like others I would think nasty internal issues are more likely.
Paul
Paul Dean

One possibility that could account for both the spray on that RH side scoop and the low indicated pressure is a bad joint between the flexible hydraulic pipe and the instrument pipe. Or may be one of the 2 pipes is fractured? They are the most adjacent hydraulic items to the area of splatter.

Steve
Steve Gyles

My opinion is that any leak big enough to drop the oil pressure significantly would have to be of an area similar to the normal clearances in the engine, so for a start at least 7 bearings with ~ 6" circumference x .001 = .042 sq ins clearance, or about a 1/4" dia hole. This would be a gusher not a spray!
So I think the pump has failed or the bearings are worn out or the RV spring is broken.
Art Pearse

The oil pumps in all 3 of the XPAG and XPEG engines I've done lately were shot. Obviously never looked at by previous owners/rebuilders.

They are the poor cousin, at the table but underfed.
MAndrus

Any update Colin?
Steve Gyles

Could the oil spray perhaps be from the front main bearing and then blow back by the fan. Is the fan oily?
My first MGA was just two years old with a very low mileage and that would drop to 30 psi when hot. I found a huge chunk of machining swarf under the pressure relief valve while I was replacing the crankshaft and shells. Those were the days - 10 for an exchange crank and shells!
Like the others say don't drive that car with 15 psi..!!!
Pete
PeteT

Update time.
Recorded radiator significantly reduced temperature from 190 to 155 - great. Not so great is, after changing the oil pressure relief valve and spring, oil pressure which is 45/50psi on start up, drops to 20psi when hot.

No oil leak visible even with the white paper trick, timing cover and fan clean and dry, but I did find oil creeping up and out of the threads on one of the Head studs which could be scattered by fan airflow.

Anyone know of a test to prove the gauge?

Sump off time.

Regards
Colin
Colin Manley

Pic attached

Colin Manley

You say sump off time but you will need to get that head off. Was it skimmed or checked for flatness before replacing the head last time?
You can get the sump off by lifting the engine slightly and using a 7/16" spanner, specially bent into a swan neck shape, you can undo the front sump bolts above the cross member.
If you replaced the pressure relief valve did you give it a whack using a steel rod to ensure it is well seated? Uncompressed the spring should be 3" long of course.
Pete
PeteT

Barney's MGA Guru site gives a good method of removing sump in car using universal joint small socket. I t works well.

Paul
Paul Dean

Connect the gauge to an air compressor with known output pressure. The compressor output is adjustable via a regulator. My gauge was reading low by about 20psi so took it apart and made a few adjustments. Can be as simple as taking off the needle and replacing in correct position. 45 degrees cold and 20 hot could equate to 80 cold 55 hot if needle set wrong by 35.(good pressures)
I actually took the gauge off the compressor and screwed it into the end of the flexi. The are both 1/8th BSP.
Hope this helps
Andy
A J Dee

Pete
The Head was flat and that aspect is good. Temp now around 150, not 190.

Andy
Funnily enough. I have just borrowed an oil pressure tester which I will firstly fit directly to the engine block connection, before the oil flex hose, then get readings hot & cold at that point, then connect at the end of the flex line. I'm hoping to find the inner hose of the braided line collapsing when warm and under pressure.

The strange thing is the slow drop of pressure that then does not rise with rpm; implying hose restriction.

Regards
Colin
Colin Manley

This thread was discussed between 16/10/2017 and 09/11/2017

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