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 Midget and Sprite Technical - Excessive Oil Pressure, 1500 engine

Gents.
Bit of a quandary.
The midget hasn't been run for 10 days as I recently had bowel surgery and had to make sure I could get in AND out of the car before I drove it again!

I took it out this afternoon for a bit of a canter and quite late in the proceedings noticed the OP gauge was off the clock. (It reads up to 100 psi). In my defence the reason I hadn't noticed was my friend was in the car for a bit of fun and she just happens to be a very beautiful woman! Mind on other things..........

At tickover the pressure drops to around 90 psi, engine hot.

All else was fine. The engine showed no signs of distress - no smoke - no clutch slip - engine temp normal and the little car did me proud, running like a dream and seriously impressing the dolly (sorry, friend) who thanked me for the ride with a big kiss.

Does anyone know if the pressure relief valve in these engines is prone to jamming closed? It looks like a simple enough task to change the spring and poppet and Rimmer Bros list them on their site. They also list an uprated spring - I wonder if that would be a worthwhile investment as the OP has always been a little on the low side, though not low enough to cause me to worry too much. About 50-55 psi at any more than 2000 rpm with the engine hot, rising to 65ish at 4000 rpm.

Any thoughts/insights gratefully received. I couldn't do much about it today except read a bit about it because by the time I got the car put away I was hurting a bit and had to go and lie down for a while. I went back out to The Shed afterwards and checked the oil level and it is fine - hasn't moved so far as I can tell. The car is due for an oil and filter change as soon as I feel well enough and I was hoping for an improvement in oil pressure after a change.

Never a dull moment with an old MG!
RS Hughes

RS
I hope/expect one of the more knowledgeable 1500 guys will be along soon but until then here's my thoughts.

You are excused for not noticing ;-) and it just goes to prove that a good blast in a MG with a dolly (sorry friend!) by your side followed by a quick snog is way better than any of the drug's our wonderful NHS can supply :-) Very pleased to hear you're on the mend and back behind the wheel.

I'm not aware of any persistent problems with the OPRV sticking and the pressures you note as your normal are acceptable for this engine. I would just pull the valve, check it's clean, free to move in the bore and reinstall. I wouldn't bother with an uprated spring as all this will do is raise the pressure when cold. If the pressure drops when hot it will drop to the same value even with the uprated spring ie the valve will be closed and the spring will have no effect.

If you want to improve pressure when the engine is hot the best approach would be to fit an oil cooler. The 1500's are noted for being hard on their oil and a thermostatically controlled cooler is usually recommended.

If you're not yet fit enough to work on the car and would like it fixed, give me a shout and we'll see if arrangements can be made.

Best of...
MGmike
M McAndrew

Thanks Mike - that's very decent of you.
I think it's the same valve in the 6 cylinder Triumph engines, of which I had several examples back in the day. I don't recall the valves being prone to sticking but you never know.
I see what you mean about the uprated spring. Cold oil pressure is not an issue, so a heavier spring wouldn't help.
I've thought a lot about an oil cooler. There is some good stuff in the archive on it and loads of discussion on other fora as well.

I have some work to finish off this afternoon but I'll get into The Shed asap and have a look at the valve. Maybe the dolly will give me a hand hahaaa!
And I'll change the oil and filter soon as.......It's been done fairly recently by the PO (I only got the car in December), but plenty of fresh clean oil is the greatest kindness you can do any engine!
RS Hughes

Hi RS,

Its usually low pressure that's the problem so most want to increase pressure.

As Mike says suggest removal of OPRV and check the spring and plunger. Also a trick to increase pressure that a lot of old MG guys did was to put a spring washer into the base of the OPRV to increase pressure a bit rather than putting in a stronger spring. John Twist on You Tube does this as a matter of course with 1500's. I have and it works well. As Mike says it might be worth checking that nothing is broken in there / floating about and jamming the OPRV shut.

On the personal front just keep to the recovery guidelines for a good summer's top down driving etc. ;-)

Cheers, Dave
Dave Squire

Mike - Dave; thank you very much for your help. I just got back from a test run.
The trouble turned out to be, er.....electrical!

When I pulled out the elephant's trunk air duct to have a proper look I saw something I've never seen before. Certainly not what I was expecting!

I first tried a few taps with a light hammer (surprising how often that works) and it made a difference to the pressure gauge for a few moments.

So I stopped the engine and had a look at the connectors. Both were a bit loose and wobbly and one of the wire terminations was decidedly unwell so I cut if off a crimped on a new one. That's the shiny red one peeping out from under the filter.

Then came the test run and Normal Service Has Been Resumed.

Question remains - what the hell is it? I know the PO was fond of gadgets and widgets and made some great mods to the car, but I didn't know about this one!

Whoops - file size too large. I'll try to resize it.
RS Hughes

Here's the little bugger! Bit blurry - the engine was running at the time.


RS Hughes

Dolly unavailable to go for a jolly today so I took the FP (Favourite Passenger)!


RS Hughes

What age is your car?

Pre '77 cars had the dual oil/water gauge, but post '77 didn't have an oil gauge, only a warning light.

The factory OP gauge was mechanical/capillary.

It looks to me like you've got an electric OP gauge, correct?
Dave O'Neill 2

well, that's a good'un ;-)

I take it your pressure gauge is a separate unit from the engine temp and not the more usual duel unit?

It appears you have an electric gauge and a pressure sensor in the adaptor. Mind you I would have expected the red/yellow wire to be the one to the gauge and the other one to a pressure switch for a low pressure warning light.

Best of...
MGmike

M McAndrew

Aye, looks like electric gauge, does that oil take off lead to anywhere? Is it a rocker oil feed kit? A lot of folk say they are bad news.

Cheers,
Malcolm
M Le Chevalier

I reckon it's an aftermarket OPRV. There isn't an oil take off, Malcolm. The fitting on the left with the new red crimp connector I think is feeding the low pressure warning light and the shiny square section cadmium plated housing presumably contains the PRV itself. The round housing presumably contains a variable resistance device to send signal to the OP gauge. This is all speculation, by the way.

I don't think the red/yellow wire is original. The PO has labelled a wire coming from the fusebox on the starboard inner wing "Oil Pressure Gauge".

I was hoping someone might recognise this contraption. It's certainly not the housing with the spring and poppet valve I was expecting.

A couple of illuminating responses though. As Malcolm says "electric gauge" - yes, there is an electric gauge on the dash. And Dave was correct independently. Electric Gauge and the car is a '78. I didn't know the OP gauge wasn't original, but I'm not surprised! And there is no capillary disappearing into the dash which is something I was looking for and expected to find.

Never a dull moment! Thanks guys.
RS Hughes

RS, I think the PRV might be hidden below that contraption. It comes out at an angle from the block below the dizzy and not straight out as in the pic. I guess you have something like this..
http://www.ebay.co.uk/itm/DURITE-ELECTRICAL-OIL-PRESSURE-GAUGE-12VOLT-052316-/110577498124?pt=LH_DefaultDomain_3&hash=item19beeeb80c
with a simple adaptor to connect both the switch and the sensor.
Check below them for what looks like a long nut but without a hole through it... That's the OPRV.

Malc, external rocker feeds are fine if fitted correctly and that's not as supplied! I did a lot of reading before fitting one to my mates engine at rebuild. Properly fitted they will help the top end which is known to suffer oil starvation in a tired but otherwise working engine. Get in touch if you want the details.

Best of...
MGmike
M McAndrew

Hi Mike,
Thanks for that.
Your post sent me out to The Shed at midnight in me bathrobe and slippers (and a woolly hat) for another look!

Nothing there. The contraption I photographed is directly below the distributor pedestal and there's nothing below it - not even a blanked port.

The contraption is screwed into the port in the block which the Haynes book says should have the angled fitting you describe containing the PRV. That's what I expected to see until I met up with this little curiosity.

So my conclusion is that it's an aftermarket device to replace the original PRV and enable the use of an aftermarket electric OP gauge.

Thanks All - I've learned something today!
RS Hughes

But the PRV is just that. It relieves excess pressure by allowing oil to by pass the pressurised system back to the sump if pressure is to high. My concern when I increased pressure was that more oil would be pushed to the rocker chamber and leave less in the sump for those thrust bearings.

How is your pressure regulated rather than measured now?

Just a thought. Dave
Dave Squire

Yo Mike

(Sorry for brief side track)

I read all about the rocker oil feeds and I just went without. Figured all the various crank bearings are much more important than the rocker gear.

The rocker gear is easy to replace and you can pick up sets of used rockers on ebay for a fiver a pop. For 10 or 15 quid you can get two or three sets, make up a good set of rockers from the lot of them and put them on a new shaft (another £20).

Cheers,
Malcolm.

M Le Chevalier

This is where the OPRV lives...


Dave O'Neill 2

What you have is an aftermarket T peice and pressure sender (electric) screwed into where item 30 goes on the above picture.
As mentioned, your year car would usually just have a green idiot light that is still wired in, so someone decided previously they'd like a number to worry about and fitted that T peice, sender and all the extra wiring (the red/yellow stuff).

If you've had a fiddle with the connections and it's reading right now, then you can just leave it alone.

The OPRV is more below where the filter sits, as shown in the above image, if it's fine, leave it alone too.

If you need something to worry about, make it the thrust washers on the rear main bearing cap falling into the sump and wiping your engine out. Or number 3 big end suffering oil starvation and exiting the block because the centre oilway is the same bore as the front and rear but feeds 2 big ends instead of just the 1 the others have to cope with.

Fit that oil cooler! Don't fit a rocker kit. If you want to fix the oil flow in these engines pull them apart and drill the oil ways properly.
Roadwarrior

Yep - All correct. Mea Culpa - I just couldn't see the PRV. Eventually I just tried shoving a light under the car and lo and behold there it was. Can't believe I couldn't see it before.

Item 30 in the drawing is the old adaptor for a capillary tube which would not even have been present on this engine as it would have relied on the idiot light, the dual purpose gauge having been deleted. I guess that adaptor would have been replaced with a pressure switch for the idiot light, which John the PO removed to fit the shiny new switch.

Thanks All. Roadwarrior the oil cooler kit is coming......
RS Hughes

This thread was discussed between 14/03/2015 and 16/03/2015

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.