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MG Midget and Sprite Technical - Oil Pressure light 1500

Have covered 500 miles now since my engine rebuild and have developed some interesting noises and warnings.

Most interestingly the oil pressure warning light begins to flicker and come on at idle and low revs (not got a reliable tacho but would guess around 600-700 rpm

This has only just started happening today. Checked oil level, is above min - put a splash more in to be sure and still happens. Engine itself is quite hot - so oil is probably thin (although the water temp is suprisingly low)

I think the engine is hot cos the mixture is a bit lean at the moment.

Interestingly the tappets are making a louder clicking noise than usual - I set them to 10 thou cold and measurered them today when the engine was hot and they were about 12! Very confused by that.

Also interesting - was bleeding the clutch the day before yesterday and noticed oil on top of the gearbox - not gallons but a fair bit... I assumed this had come out of the breather, but now I'm thinking the engine might have lost some oil... but how would it get there?

All in all, I'm a little worried because the oil pressure gauge sensor is set for 7psi, which is v low. I wish I had a pressure gauge so I knew what it was doing exactly. I'm considering doing a full change to see if there is any crud in the oil/filter - I'm wondering if the pump is okay... or if there is blocked pipe.

If I stick my foot down and rev up then the light goes out. Am I being paranoid?

Thoughts very much appreciated.
C L Carter

What grade oil are you using ?

Tickover probably a bit low if your estimate is right.

Any grumbling noises when accelerating under load and from low revs.?

as Guy's put

plus you'll have to describe the noises and warnings more

if the tickover sounds hunting or as if it's going to drop into a stall increase it a bit

if the mixture is much too lean across the used range of revs I'd have thought the water temp would have shown it

if you're running on 95 octane how does it normally run on 95 and bear in mind you might be pushing harder on this trip

how much oil do you think you've used, have you changed the oil and since the rebuild

oil on gearbox, if you could get a drop to put on a tissue or smear on your hand to see the colour and thickness or smell it to see if it's engine or g/box oil
Nigel Atkins

What oil are you using and what is the state of tune of the motor?

I take it you do not have an oil cooler fitted?

On a properly built 1500 I would expect the hot idle oil pressure to be not below 20 - 25 psi, so if your oil light is coming on there is obviously a problem.

Did you replace the oil pump and check the tolerances on it during the rebuild?

What machining work was done and by whom? (eg what B/E and Main clearances did they set?)

Did you check the oil pressure relief vave for correct operation?
Deborah Evans

Also, are you sure that your coolant isn't low ?

On my 1500 the temp gauge dropped when the water was low as it left the sensor in the head "high and dry" on one occasion. As l was then driving along wondering why the engine was behaving as if it was hot, whilst the gauge said that it wasn't, it then blew the HG !

So I'm running the Halfords 20w50 oil - have done for a while now.

No work done to the lower part of the engine - just the head. Crankshaft and pistons never removed.

I cleaned the oil pump filter but didn't do anything else to it. Had no time.

Coolant is fine.

Yes Guy there are grumbling noises from accelerating in 3rd from low revs... but the whole car is a bit shakey on its new stiff engine mounts so hard to tell what noises are what. I thought that was the sound of the carbs not drawing enough mixture - but I'll have a listen on the way to halfords and see if I think its the bearings.

C L Carter

It may be a good idea to fit an oil pressure gauge - invaluable on any car and especially on the oil vulnerable 1500. Then you will know exactly what the oil is up to.
Oil leak from rear could be the oilway plug, HG or the core plug at the back end of the camshaft.
Bob T

Oil pressure gauge on my list.

I think I've diagnosed problem. Water expansion tank I think was overful... It was hotly the brim when I checked it... Which I would kind of expect when hot... But when itcooled it was over halfway.... So I've taken a bit out and now the temp is better and mght hasn't come on today. Frequent oil checks suggest I'm kt losing any oil. I thnk its just thinning from overheating.

So today the water temp gauge caught up qth the engne and after a shqirt stint on the motorway it was reading almost max.

mixture in cyl 4 was fine after checking with colourtune

Am now heading to base camp in yorkshirr and am taking it easy. If the light comes on when driving I'll get recovered back to London.

Sorry for all the typos.. am struggling on a mobile device.

C L Carter

I take it this wasn't happening before the rebuild?

Oil pressure switches fail, how old is it? Easy to replace. If it's just become too sensitive to low pressure, it will be giving a false warning. As long as it's going out, below 1000 rpm, you be ok, your making oil pressure, but swap the switch to be certain.

I had this on my girlfriends Triumph 1500 saloons. 1 auto and one manual. Drove them for a couple of years before attending to them. You can drive the engine with a flashing oil light for thousands of miles, even if the oil pressure is low at low revs. Not great, but it will last for quite a while.

Very unlikely that the oil pump will fail completely.

Most likely, assuming switch is ok, is worn/wearing ends. If that's the case, then it's a bottom end rebuild anyway, but you might as well complete the UK tour.

If it starts heavy rumbling(mains), or rattling off load (big ends), from the bottom end, then take it very easy, or else you might be in for the cost of a new crank.

Try and cool it down for sure, but if the cause is the bottom end, it will likely over heat anyway.

edit. You posted whilst I was composing. :) enjoy the tour.:)

Lawrence Slater

Always difficult diagnosing engine problems from a distance, but if it were my car I would be thinking this:

Low oil pressure on tickover when hot - oil is getting too hot and too thin. Not uncommon for a 1500 without an oil cooler, although maybe less common at this time of the year, as ambient has been quite cool.

Grumbling noise is common enough on part-worn 1500, especially if the oil gets over warm. One reason I used to renew bearing shells as a 25K mile service item (and I had an oil cooler)
Erratic water temp on the gauge would suggest to me a potential or incipient head gasket problem. If it is beginning to go this could account for engine feeling hot and the oil pressure getting so low.
If you removed the expansion tank cap when it was hot you would have de-pressurised and let air into the system. Then as it cooled it would draw less water out of the expansion tank so this may then appear overfull when it had cooled. You could at this stage have air in the cooling system - explaining where the extra volume of water has come from. With an expansion system it isn't possible to overfill as the car will eject any surplus via the overflow as it heats up anyway.

My suggestion is that you re-torque the cylinder head bolts. If it is the beginnings of HGF you may catch it in time and be OK for the rest of your holiday.

Having re-torqued, then reset the valve clearances. Double check the coolant levels, squeezing the larger diameter water hoses repeatedly to make sure you pump any air out. Same reason, release the top hose to the heater core and trickle-fill from there to make sure you have no air lock. Run it up to temp and then let it fully cool again without removing the filler cap. Then check and top up the expansion tank again.

Maybe richen the carbs by turning the jets up by 1 or maybe 2 flats. It may just keep your temp under control a bit.

Top oil level up to Max mark (up to min mark is not enough!)

Away from home it is not so easy (but not impossible!) to do much more than that. Hopefully there is nothing wrong and you can enjoy the rest of your holiday!

Good luck!

I'm with Guy again, possibly HGF problems

whilst it's never a good idea to ignore oil warning lights and it might on this occasion be doing it's job back in the day the lights were often disconnected to stop them flashing on too frequently - of course without a light you wont get that warning and if it's unreliable it's a crying wolf situation

keep oil and coolant to max to allow for dissipation and with coolant top up with mixture not just water or you're diluting your protection

take it steady don't race or labour the car, avoid stop/start or congested roads 40-50 mph in 4th gear on open roads as much as possible

check your fanbelt isn't loose

check pressure cap seal

check your heater vale is fully open and function to take a little heat away from the engine

avoid getting the temp gauge anywhere near H zone

look for white vapour out of exhaust

if you need to limp a short distance consider removing pressure cap

if you're going to a motor shop you could consider adding some type of Wetter-Water product
Nigel Atkins

Nigel has added some good suggestions there.
But don't let it ruin your holiday! Just take it easy for a bit. keep an eye on things and monitor how it is going. If all seems well, and your confidence in it builds then open up a bit and enjoy the famous roads that you have been recommended to try! If the worst happens, then you have your smartphone and your break down recovery to get you out of trouble.

If in the Lakes or western Dales, and in need of help - 07738 712 117

I had the HG go on my present midget on the way to the start of a long weekend tour but as I knew the engine was good with fresh clean oil and filter and the engine block waterways were clean and clear along with rad and heater matrix I slowed down, a bit, and I just kept topping up the coolant and enjoyed the holiday

I was in Norfolk and Suffolk so no steep hills mind

I limped back home at the end of the tour at night when it was cooler and uncongested and at 50 mph on mostly dual carriageways to get the most uninterrupted cooling air to the rad and engine

So dont let it spoil your holiday but adjust your driving and plans based on what you know about the condition of your engine and the amount and depth of work and servicing youve already done

if you have to add a lot of coolant make sure you get in as little air as you can and get out all the air you can
Nigel Atkins

just noticed I lost the last line off my last post and I'll expand it a bit

. . . if you have to add a lot of coolant (from cool obviously) after the usual fill up procedure of - fill, cap on, run at fast idle for 30 secs, switch off, top up and run up to normal temp, switch off, let fully cool down

then check and top up if required but this time leave the cap off and run engine looking for air bubbles in expansion tank, give it a good while for the bubbles to stop if you have any, if they don't stop after a reasonable time then you have either the answer or at least part of the problem
Nigel Atkins

Finally made it to my stopping place. Air in fast was a problem... But didn't cure it fully. By the last mile... Loud clicky rattle noise was getting worse and evident at more revs... Oil pressure light on at normal driving speeds. Also new problem... Nasty noise from brakes... I suspect pads down to steel due to a problem I raised a long timeback about my front brakes being always on.

All in all. All signs point to recovery home to London.

Sad times.

C L Carter

That's bad luck Christian. Always a next time though. So you just have to chalk it down.

If you'd been driving these, and other older cars back in their day, this would't have been a first, or a last, and that way you learned to avoid it.

Newer engines are bullet proof by comparison, but in good nick these can be too. No doubt yours will rise phoenix like pretty soon.
Lawrence Slater

Yrs, that's a shame Christian.
Where about a are you. Having got there are you staying a couple of days or organising a recovery straight away?

I'm at my Mums house in Knaresborough (just outside Harrogate). Rang the Autoaid man this morning to arrange recovery for tomorrow morning - but was told I can't prebook jobs so will ring back tomorrow morning.

Fortunately the friend I'm travelling with left his Rover P4 at his Aunt's house in Harrogate and so we are going over to the moors in that for the day. Not all is lost I guess.

I had another look at the car this morning, I think there may still be air in the rad but I'll be damned if I can burp it. I gave the top hose a few squeezes with the exp cap off then took off the thermostat filler plug and it began to suck the water out... the expansiontank was filling up and overflowing and the filler neck was going down so I started filling it up as it did this thinking it would draw out any air lock itself... but this went on for a long time. I am very perplexed by this - went for a drive from cold and oil pressure not a problem however low the idle. The rattling noise only came back when the engine got up to temp which suggests the problem may not be permanent bearing or camshaft damage... but then the brakes are still a problem - and dangerous so driving home is a nono - I think I'll need new discs too.

Arranging for recovery man tomorrow then when home I will sort out the coolant. Might be worth draining and refilling from scratch. I will have the sump off and inspect for white metal etc, will inpsect the oil pump.

Depending on results of that, I might take a big end off and inspect.

New oil filter and change the oil... and then see how it goes.

Of course will have the brakes apart aswell.

C L Carter

Christian, I was thinking I might invite myself over to meet you and inspect, but you are a bit further away than I had thought. Nothing I could do to help anyway!

Regarding the brakes not releasing, the commonest cause of this is old flexible hoses that degrade and swell internally, and then act like a one way valve. Brakes work fine when you press the pedal, but don't release cleanly when you take your foot off again. Simple fix = fit new hoses.

Rattling is likely to be engine bearings as it gets worse when hot and given the low oil pressure. But it just could be a blowing exhaust manifold gasket - it is surprising how metalic this sounds - a clack, clack, clack noise.

Lots of water loss and air entrapped in the cooling still sounds to me like a HG fault.. If that was the case it would cause overheating (despite what the gauge showed) and that in turn would thin the oil, and that in turn could run the bearings. It is an easy, though messy job, to drop the sump and remove the bearing caps to check the state of the white metal shells. Check the oil for particles, although you wouldn't necessarily easily spot debris from bearing shells unless they had really disintegrated!

If the journals haven't scored and are not oval, then you may be able to just refit new bearing shells and get away with it.

Christian, you said:
"took off the thermostat filler plug and it began to suck the water out... the expansiontank was filling up and overflowing and the filler neck was going down so I started filling it up"

Not quite clear on this. The Expansion tank is below the rad filler cap. If you remove the expansion tank cap and pour water in through the rad filler plug it will just run through and the expansion tank will continue to fill and eventually overflow. You need to fill the expansion tank to the max mark, put the expansion tank cap on properly, and then continue to top up at the rad filler plug. The expansion tank, being sealed by the spring loaded pressure cap, won't then simply continue to fill and run through! When it is full at the filler plug either "burp" the pipes or run for a bit to allow it to heat up and expel the air. Then fit the rad plug.

The heater core is higher than the rad plug, and this can end up with an air lock, even after you have done all of the above. It is less critical to cooling, but you still need to purge the air out of that too. When the car has cooled, disconnect the top hose to the heater core and refill through there. Don't remove the expansion cap as you do this or you will simply be overflowing the expansion tank again.

As you are going to get it trailered home anyway, it is probably best to leave this till you are home. And then it would be worthwhile doing a thorough flush and clean out of the cooling system. Nigel will fill in the details on the procedure for this if you need them!

I'm reluctant to think its a head gasket failure... Its brand new - composite - and I retoqured it before I left. I put it on dry though... I know a lot of people who use wellseal to help seal it but I don't think that necessary and it makes it impossible to remove later.

I will have a look at the big ends at the weekend.

Exhaust gasket I think is doubtful - its a composite one not metallic like the one that came off. When running there is no sign of combustion leakage from anywhere either.

The rattle only occurs under acceleration... and although it sounds like an engine noise, I'm trying to convince myslef its the carbs (which seem to lose damper oil very quickly) - thought the pistons my be rattling around at a particular freq - but this i think is wishful thinking as the car is behaving itself in terms of throttle response.

C L Carter

Maybe not HGF then, but why else would it loose water and run hot then at this time of the year?

Maybe it was never properly filled after fitting the head. If it was just filled to the max mark via the expansion tank, then the system would only be about 3/4 full and would have had lots of air in it.

Hi Christian. My experience of big ends, as opposed to main ends, is that the mains make a heavy rumble all the time if bad, but tend to show as low oil pressure first.

Whilst, until they get pretty bad, the big ends are a lighter rattle, which is only noisy when you are neither on full load, or off it. Pulling hard tends to seat the ends firmly enough to stop them rattling, but as you come off the throttle, the crank sits and rattles between the shells. Once past this point though, noisy all the time.

I agree with Guy though, if it's rattling as a consequence of heat and low oil pressure, then either it's a very buggered cam/followers, or it's the ends. Sadly if you can't eliminate other engine rattles, it's sump off time.

Still, nice compensation touring in a P4. :)
Lawrence Slater

I think exactly that Guy, I drained the car to fill with antifreeze before I set off - and clearly left an air gap when refilling. - surprised i didn't notice in the first 2-300 miles though.

Will be having the shells of the big ends on saturday and will report any damage. Will also measure tappet clearences to see if the cam followers are worn.

C L Carter

Whilst you have the sump off, check the condition of the crank thrust washers as well. I don't think they will have had any significance with your current problem, but they do wear and can give other problems. (clutch, conrods etc) Easier to check and replace if necessary whilst you are in there!

If the rattling noise is under acceleration, are yopu sure that it isn't pinking? That would cause rapid overheating and lots of other trouble as well! Try doing a check on your timing just to be sure,
good luck,
Graham P

Ooh good point! ! It definitely was pinking... because - I turned the ignition off at one point in order to coast to the nearest parking spot and it was pre igniting - I assumed it was pre igniting because it was hot - not because it was causing the heat.

I set the timing to 10 btdc before I left - but will check that when I get back. Thanks for the pointer.

C L Carter

Never experienced knocking before - so youtubed for engine sound... came across this video. Whilst I'm not sure his video is accurate of helpful - the sound from my engine is not a million miles away from the sound in the video - only it occurs only when under acceleration.

I will start with the timing gun to see if the dizzy has moved when I get home.
C L Carter


I had very similar symptoms many years ago while on holiday in France. The points had closed up which caused over heating which blew the head gasket :( After waiting for the engine to completely cool I reset the points re filled the cooling system through the plug on top of the thermostat housing (not the expansion tank) and then drove carefully back from Le Mans to Warwick with no other ill effects,a simple replacement of the gasket and all was well.
Good luck Carl
C Bintcliffe

Sorry to hear of your trouble Christian. I agree with the advise the other Midgeteer's have posted. One thought occured to me - if you brakes were binding - this would have mean't you would be pulling more load for any given road speed - so you would be more likely to overheat - and without an oil cooler - this may have then triggered your pinking and pre-ignition...

Hopefully your pre-ignition wasn't bad enough to do serious damage to your engine...
John Barber

Thanks for all your comments and help everyone, much appreciated.

I have started work on the brakes. The pistons were stuck solid and couldn't shift them... compressed air made them go with a bang... and I almost crushed my hand to dust at the same time. Cause of problem, combination of corrosion and brake hoses... see photo of one cylinder. I'm amazed there is any hose left!

I tried to demonstrate sound to a friend when I returned as was unable to reproduce it or get the oil pressure warning light back on again, so maybe there isn't any permanent damage.

I checked timing, and it was where i set it before I left at 9/10 dbtdc which is where the books says to leave it. (before my engine rebuild it was 14, but if I put it back to that it would make it pink more so I'm happy with the timing)

Carl, thanks for the pointer (get it, pointer =]) I will check those tomorrow, and I suppose it could also be the condenser... I hadn't thought of electrics at all!

I am reluctant at the moment to drain the oil and check the bearings/pump/sump until I have found the cause of the problem.

C L Carter

Oh btw, here is a funny story... well its funny now, wasn't at the time.

Managed to trap my hand in the brake cylinder under hydraulic pressure.. probably due to the fact that there was broken up hose clogging the pipe work.

It was very painful, and the only to separate it was to split the calliper in half - but it took me 10 mins of pain to work that out.

See photo

Just goes to show, you should think things through before following the instructions blindly! What an idiot! When you are in that much pain, it is pretty hard to think clearly... the only thing going through my mind for ages was 'how am I going to explain this at A&E'

It must have been really clogged up in there cos craking the bleed nipple did nothing...

C L Carter

and the effects

C L Carter

You did well to get yourself out of that!

I had a friend who managed to trap his hand between a wall and a 3mtr length of kitchen worktop,after a lot of thought he had to shout for help. The help eventually arrived with the fire brigade who broke open his door and then cut the new worktop in half!!

So it could have been worse :-)

C Bintcliffe

>>following the instructions<<
really !?

>>When you are in that much pain, it is pretty hard to think clearly...<<
that explains why you thought to photograph it :)
Nigel Atkins

Everything must be documented nigel!
C L Carter

I think it's more a generational obsession with photographing everything that happens, usually on the main obsessional item the mobile phone

the document I want to see is the one that instruction you to put your hand there!

seriously Christian try and avoid damaging yourself as you may think you'll fully heal but 20 years later you could find you haven't and wish you hadn't got the injury in the first place - ask another old bloke he'll tell you :)
Nigel Atkins

The instruction didn't say "remove hand" - I was the one who should have used some common sense... but I was thinking... that compressed air would barely budge it... let alone move it enough to crush me.

Yeah... I might injur myself... or end up with some horrible disease due to all the horrible crap I get on my skin/lungs... but whats the alternative... grow old and have my indoor safe hobbies like computer games... no thanks... I'd rather be dead early and have an MG!
C L Carter

live longer and enjoy your Mgs more and for longer

plus they're easier to drive with two funtioning hands

just be thankful it wasn't your camera hand :)

I wont mention you were more interested in fiddling with your engine than fully sorting your brakes before you went away - you'll learn prevention is better than cure on your car and your hand :)

get any good drives in and good pubs?
Nigel Atkins

Yeah the 2 drives you recommended in the Peak District. Stunning, even with hailstones battering me down

C L Carter

good, they'll be even better in fairer weather

keep the lists of other roads, places and pubs for next time

if you were relayed back this time just think of the petrol costs you saved :)

pity Lawrence has missed your hand incidence I'm sure he would have approved

we'll watch with interest to see if you keep your hand in withyour car repairs - boom, boom, tish

not so much a handbrake as potential hand break

Nigel Atkins

This thread was discussed between 10/04/2012 and 14/04/2012

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