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MG MGB Technical - How is my engine not toast?

Scenario:

Started my MGB, and joined the motorway after a few miles of local roads. All running normally pootling along at about 60mph in the slow lane until I happen to glance at the oil pressure - it had dropped to 0! (I hadn't looked at the gauge before then). Did the tapping of gauge to check that it wasn't faulty/stuck, then a few minutes later, started to lose power (no other knocking/ other weird noises etc) so pull over on to the hard shoulder. Not sure when the oil pressure had dropped, and I had done a total of 27 miles since setting off by then. A quick look under the bonnet revealed oil everywhere(!) and a small pool of oil under the car on the hard shoulder.

Breakdown truck tows me to my usual garage (we don't try starting the engine). Garage finds that there's been a catastrophic failure of one of the recently replaced oil cooler hoses - failed at the metal connection where the two metal bits are swaged together - the two bits had just popped off and separated!

The garage was able to turn the engine over - nothing seized, refilled and checked oil and checked over oil pressure etc - it all seemed ok and they said I was very lucky.

That happened a couple of months ago, and since then I've been driving it a bit tentatively (keeping to local roads) just in case - pressure is much as before - 50-55psi ish at idle and 60psi maybe a touch higher when not at idle. Takes a little while to get up to full oil pressure when starting from cold. Oil is clean, and no metal bits on the dip stick. Oil consumption is not high and no burning oil smells or any weird noises. Engine pulls strongly as before.

How did my engine not get totalled? Perhaps the loss in oil was sudden and not gradual with a sudden rather than gradual hose failure? But how would that cause the loss in power?

Thoughts welcome!
Nat

Nat, ah the dreaded burst oil cooler hose! Back in the day when this happened folk often used to bypass the cooler with the remaining hose.

I'm guessing the engine was starting to seize, hence the loss of power. However, there was still enough oil getting to the mains and big ends not to wreck the bearings. Personally, I'd just carry on until the engine needs to come apart for another reason. When you take it apart you'll probably see some scoring on the bearing shells and scorch/seize marks up the pistons. What was the temp gauge saying? Just before catastrophe it would have been off the clock, but you didn't quite get to that point. Engine oil, of course, helps to keep the engine cool. It would be interesting to do, or get done, a compression check to see if the pots are all even, preferably over about 125psi.

Something similar happened to me many years ago in my Riley on a fast run back up the M5. A connection had come loose on the oil filter conversion and I lost most of the oil. That resulted in one big end's white metal breaking up and bits of piston ring coming up past the piston, but that happened a little later. I don't think I'd picked up on the situation as quick as you did!

Let's see what others say.
Peter Allen

I suspect you looked at the pressure very soon after the burst. You lost power as the engine got very hot and normal combustion was no longer possible. If it had run on, it would have wiped the white metal bearings. As things turned out,it had not yet reached that point and anecdotal evidence might suggest the day was saved by the additives in the oil. You don't say how much of the secondary coolant was left in the radiator afterwards.
Roger Walker

"then a few minutes later, started to lose power"

Gordon Bennett! I'd have pushed the clutch in and switched off as soon as I saw it. I think you were very lucky - but may still have bearing damage. Whether it started losing power because it overheated or the bearings started to seize is arguable. I had a an air-cooled 2-stroke do the same thing because the oil dispenser wasn't working so ran for a while on neat petrol, that was definitely seizing as it stopped as soon as I pulled the clutch in. You could drop the sump and check the bearings for damage, or carry on and perhaps risk more damage to the crank.

The oil gauge hose is another cause of total oil loss, I have added a pressure switch and warning light to both mine. The North American oil switch adapter on the heater shelf for the anti-runon valve that is the connector between the gauge hose and the metal pipe makes this very easy - if you can find one. I do have a couple and can convert the existing connector as well.
paulh4

Nat,
I'm with Peter keep an eye on it and just carry on, an engine car run a surprisingly long time without oil.

You say oil consumption is not high, what was the oil consumption before and what is it now?

As said the engine oil does cooling, hence the oil cooler too, your scenario is exactly why I use a high quality oil to handle things better for longer and why I have the 'water' cooling (/heating) system as clean and efficient as possible. Even when properly cooled engines get hot and waste a lot of heat (power).

If you must have an oil cooler then it really needs an oil thermostat so that, in the same way way as the 'water' cooling, the oil is not cooled when not required and slowing engine and oil warm up and slowing or preventing the oil getting to a good operating temperature. Even out of winter the oil cooler without a stat could be overcooling for far too long and on shorter journeys preventing the oil getting to a good operating temperature.

The more items you the more potential for problems, plus the oil cooler and its hoses hold oil so at oil changes more old oil is left in to more dilute the effect of adding fresh new oil.

Personally I'd be looking at doing another (hot and thorough) engine oil & filter change within a number of hundreds of miles - and using a better high quality oil for belt and brace and ease of mind.

No doubt you are doing it now but a good habit to get into with any vehicle is put the ignition on without any (but safety) electrics on, wait and check the warning lights and gauges whilst you put your seat belt on. Start the engine and for a number of seconds again check the warning light and gauges and listen, look (and smell) that things are as they should be before turning on electric items and pulling away. When parking up, turn off all (but safety) electrics and for a number of seconds check the warning lights and gauges and listen, look (and smell) that things are as they should be before turning off engine (and safety electric items).

I was on a tour when a newly rebuilt engine in a BGT V8 lost its oil, the oil cooler hoses hadn't been held correctly and one sawn throw, luckily it was soon noticed but the engine bay was no longer as clean.
Nigel Atkins

A relation of mine had mentioned that he had heard odd noise from the front of his MGB engine and when we had a look at it, we decided that it was the water pump bearing.
It wasn't wobbling about or leaking and I said that it would probably be ok to run it for a month or two and that I would help him fit a new one over the winter.

I hadn't heard from him for a while and called him to ask if he had got the pump yet.
He went quiet over the phone and said "I don't really want to talk about it!"
Apparently, he had decided to fit the pump on his own and had suffered a bit of an engine problem afterwards.
He said that the pump swap had gone well and that after topping up the coolant level, he took the car for a 10 mile test drive.

After 5 miles or so, his wife said, "Have you seen the temperature gauge"? which was showing way beyond hot! So he decided to turn the car around and drive home as fast as he could!

When I asked how he engine had fared he said that he may have blown the head gasket because it had began to make some strange noises by the time he got the car home.

I went round with my spanners and we took the head off. The good news was that the head-gasket was fine, but the bores, pistons and bearings were less so!!!

He was a bit puzzled that this had happened because he had made sure that he had fully topped up the coolant before he set off.
When I asked him how much coolant he had put in, he said that it would only take a pint!! and he was genuinely surprised when I told him that it should have been nearer to a gallon!
However, he then pointed to the expansion chamber lower down on the inner wing and told me that it was full! and that he hadn't actually drained out the coolant when he swapped the water pump.

He only realised the extent of his error when I explained that the pump is at the bottom of the cooling system and so he had actually completely drained it.
I also asked if he had not considered removing a top hose and pouring the coolant in through it?

But, he obviously didn't really understand how things work and, as a result, his £30 water pump cost him nearer to £2000 as a re-con engine from Ivor Searle.

A very steep learning curve.

Cheers
Colyn



Colyn Firth

Nat. My daughter had the same problem many years ago--oil cooler hose broke when driving. Unless you drive with your eyes on the oil pressure gauge, rather than the road, or you just happened to be glancing at the gauge when the final loss of pressure happened, you do not know how long the erratic pressures was going on. As such, I would agree with Paul Hunt that, as a minimum, dropping the oil pan and checking/replacing the rod bearings is inexpensive insurance against bearing failure. If the bearings fail, it can cost you the entire engine. The engine in my daughter's car demonstrated rod knock when restarted after the oil cooler line was replaced and, when examined, showed sufficient damage that the crankshaft had to be ground down to the next undersize (.020" from memory). Maybe you escaped with no damage to your engine. But, probably not. Suggest you check out the bearings.

Les
Les Bengtson

"So he decided to turn the car around and drive home as fast as he could!"

Something else I wouldn't have done!

Even with the earlier systems you can sometimes only get a small amount of coolant in if the thermostat doesn't have a bleed hole or valve, I've had to drill a small hole in mine.

Even after a pump change there is still quite a bit of coolant left in the block if the block drain doesn't work, which is why when refilling other than a completely dry engine you should put the required amount of neat anti-freeze in first and then top up with water, not use ready-mixed or it can end up over-diluted.
paulh4

Nat,
you're probably looking at his gauge too much now.

Allowing for the gauge is just a gauge and as long as it shows what is normal for the car I was surprised at the 50-55 at idle but again its a gauge, 60 running, ok but "Takes a little while to get up to full oil pressure when starting from cold" what does that mean?

I'd expect the readings to drop as the oil gets warmer. Again the oil cooler without stat will slow the oil warming and may even prevent it getting to a good operating temperature on (very) short journeys.

No one can deny a check of the bearings is better than not but it depends on your circumstances and other factors of its value to you and only you know that.

You say oil consumption is not high, what was the oil consumption before and what is it now?
Nigel Atkins

Thanks for all your comments-

I have been looking at the gauge a lot now, and have being doing what Nigel suggested re looking at starting and at parking up.


Oil consumption before was maybe the equivalent of 5mm -ish on the dipstick after a couple/few hundred miles. Now, I've probably done maybe 150 miles since, and the oil level hasn't changed. Admittedly, there was a very slight oil leak before (leaving a single small spot on the ground), but when the garage were looking at it post incident, they said that they had tightened everything up whilst checking for leaks.

My temp gauge was not working at the time so I didn't have any indication of temperature reading, and the garage mentioned that they had topped up the coolant in the radiator, but not that it was empty or anything (I had topped up the rad prior to starting the journey).

If I start the car up when it's cold and haven't driven it for a while, the PSI hovers around 45ish at idling speeds, before going to the usual 50-55ish at idle after a little bit of driving - maybe after a few minutes.

I'd to use it to go a bit further than localish journeys- so checking the bearings is probably worth it for peace of mind - I don't fancy a totalled engine or being stranded somewhere!
Apart from scoring or physical damage/change in shape of the bearings - what should I be checking for? I guess I wouldn't be able to see if the bearings had been inadvertently heat treated...


Nat

Damaged bearings would have to be very bad to affect oil consumption and by then they would probably be rattling and knocking. If oil pressures are the same as before then it's unlikely you have done major damage.

Cold start mine runs at 70 on the fast idle, 80 when running, not much less than 40 on a hot idle. However the longer you leave it idling i.e. in heavy traffic on a hot day the lower it will go, although I've never seen mine below 25. Book figures are 10 to 25 idling and 50 to 80 running, between those is fine.

Checking them after an event like this should be just a matter of inspecting the shells to see if there is any copper or steel showing through, and the journals for scoring. Only if you were checking for normal wear would you bother with something like Plastigauge.

Don't try and remove the rear main bearing cap, you can check the lower shells on the other bearings, the upper half is likely to be the same as the lower so no point trying to fish that out. Easier to check both halves of the big-end hells but again I'd only bother with the lower half. Only remove one cap at a time, and ensure you put them back the same way round as they came off. Afterwards go round all the nuts again to double-check they are tight.

Or just drive it, after replacing the dual gauge.

paulh4

Nat,
whatever your oil level is on the dipstick now leave it there - provided it's near the Max mark and the dipstick is the correct one and oil pan is original. On my (A-series) engine it never seems to like being on the Max mark but about 5mm below and will sit there, or about, for hundreds and thousands of miles depending on how and where I've been driving.

You can do without an oil pressure gauge, though as you have found it very useful especially if you've got an oil cooler with hoses - do strongly consider an oil stat if you're keeping the oil cooler. But a 'water' temperature gauge is perhaps more useful and if you want the combined gauge then you have both anyway.

Let me assure you having had 4 replacements dual gauges that I can remember despite the factory calibration marks and the testing them to pass quality when fitted the 'water' temperature at least does not correspond to what is expected in my experience and I suspect the oil pressure isn't spot on either so don't worry too much about actual numbers (if your gauge has them all) just that the needles don't deviate from where they usually show in real world use - subject to your oil and coolant systems functioning about as they should.

At my last installation of the dual gauge the 'water' temp read even lower than the low readings given by previous gauges so I contacted the manufacturer and later decided I couldn't put up with this even lower needle position and had it replaced via the supplier. The 'water' temp capillary tube being massively overlength is a PITA to fit so replacing it again so soon didn't make me a happy bunny.

The current oil pressure gauge shows higher than at least the previous two by a little bit but the 'water' needle moves around it's previous gauges locations, under reading as the others before and even as the previous same MG model I had. IIRC my MGB GT needles were about book figures but that gauge might have been original to the car when new.
Nigel Atkins

If you don't have an oil pressure gauge you should definitely have a warning light!
paulh4

Ah, thanks. Paul, based on your comments are you suggesting that maybe the bearings are not too badly damaged or that it'd be worth having a look anyway? (I'd probably need to take it to a garage to drop the sump as I don't have that much space/ramps).

The current oil level is on the max line and hasn't budged.

I have a dual gauge - the water temp bit only recently failed (I had to replace the heater valve), and it hasn't worked since. When it was working, the needle would sit happily around the N mark, and would creep up if stuck in traffic in really hot weather for ages. Oil part of the gauge is still working ok.

The oil cooler was already on the car when I bought it - but will look into the oil stat too.
Nat

Nat
I'm a tiddle interested to know what engine oil you are running in your car
You mention 45psi oil pressure idling cold and that increases to 50+ after a drive
Usually that is a sign that the oil is a bit too thick, --could be the oil choice, or the oil choice compared to ambient temp-
Just interested, 45psi's ok don't panic ,it's just a question
willy
William Revit

Nat I think I'd be having a look, shells can wear and the more they wear the more they will damage the crank. Haynes recommendation is to change them at 30-50k for 'maximum engine life' by which I take it to mean delaying the need for a crank regrind. Oddly it's 30k for big ends and 50k for mains, but after a couple of cycles you would be doing one just 10k after the other. Big ends are easy, mains less so.

It's quite easy to damage the capillary tube on the temp gauge, care is needed anywhere in its vicinity.
paulh4

For those worried about low oil pressure you can always fit a low pressure warning light - maybe not to the extreme I have in my coupe!
Pressure switch in the line to the oil pressure gauge, activates when oil pressure drops below 42 psi.

Cheers
Mike





Mike Ellsmore

Fairly early on in my ownership I bust the capillary and at that point converted the dual gauge to two separate gauges, picked up cheaply at autojumbles (ebay?). The oil gauge hooks up as before, and the water one is now electrically operated off a sender screwed into the old capillary hole. The extra gauge is one of three in what were the air vents in the dash (radio in early cars).

Agree with Nigel, that of the two gauges the water temp is the more useful, but if I was to have no other gauges, I'd have these two.

The problem with Nat having a look, and I'm guessing he'd be farming this out, is where does he stop? Without a major strip down he can't look at the mains. If the big ends are a bit scored, does he just replace the shells, or does he gets the big end journals mic'd? If they're out of whack, what does he do then? And that's before we get to the pistons.

I'd just get that water temp gauge fixed/replaced and monitor.......
Peter Allen

20psi for mine on the roadster, but a more conventional 8 on the V8 as that frequently drops close to 10 in traffic in hot weather. As Roger Parker once said based on his Police experience of these V8s "What hot idle oil pressure?"

Seeing Mike' large orange light in the roof reminds me of a Prescott hill climb many years ago, and a Scimitar on the Start line. I was wondering what the large (it was a Mini indicator lens) orange light on his dash top signified, glowing as it was, and when he shot off the line the large and spreading pool of oil gave a clue. He must have gone a couple of hundred yards at full chat before he noticed and took an escape road and got back to the pits. The oil filter had come loose, but replaced he got another ago and ended up with FTD.

We did without temp gauges for decades, on MGBs they seem to be mostly a source of paranoia.
paulh4

I can't remember such very low hot idle pressures in the Rover V8 engine'd vehicles I've had, but I am perhaps fussier about what oil I put in them. 😉
Nigel Atkins

William, I use 20w-50 oil, the Halfords classic car green engine oil which is probably like Duckhams. I haven't had such lowish oil pressures recently, but that might have been because the overnight temperatures haven't been as low compared to a month or so ago (hovering around 0 deg c)

Yes, I'm mindful that I may get stuck in an ongoing loop of escalating actions post dropping the sump to check out the bearings & I would be looking to get the garage to do the work.

Is there anyway of salvaging the existing dual gauge with a replacement capillary bit?
Nat

Halfords is (or was last time I looked) Comma, Duckhams is really just a brand now and is, wait for it, now Comma (or was last time I looked). It'll probably be in the Archives here from me but note the dates as Duckhams was sold again after relaunch but I forget the years and details. Sufficient to say any oil you buy today won't be the same as if it was around in the 60s and 70s (and ZDDT isn't the only fruit).

Nothing wrong with the Comma oil(s), lots of owners use it, you could do better or better still but it depends on your expectations and if you actually drive or use the car and in what manner.

Oil pressure is generally higher at cold starts not lower, it drops as things warm up (if they're allowed to warm up sufficiently).

Short answer to repairing capillary is yes/maybe depends were it's broke, for full answer see the Archives here or midget and Sprite Technical or MGA or MG TD-TF, I've seen it somewhere in the past, not the type of thing I'd attempt or probably be capable of.

Paul Hunt's site is excellent (other perhaps his old-fashioned and out of date views on oils, but I would say that, there I did) if you've not already seen it, the repair answer I might have seen there too. - http://www.mgb-stuff.org.uk/hammertext.htm



Nigel Atkins

Oil pressure at cold start lower tgan warm can be an indicator of excessive resistance (partially blocked cooler or filter) or viscosity too high, latter especially in winter.

I encountered onr (highly rated) brand claiming 20w which poured like treacle in the winter and would not pick up any pressure on a frosty morning. It did later in the day after the sun came out, but pressure was low until the engine warmed up. This was on a newly built engine only done a couple of hundred miles.
Paul Walbran

I use the same oil and don't get that effect. It went straight up to 80 first thing yesterday i.e. after a near zero night and not having run for a week or so.

Given this positive-displacement pump I'd have thought that once it picked up oil it would have built up full pressure, although if there is a restriction near the pickup it can 'cavitate' and pressure drop right down at very high rpm. Perhaps there is a small air-leak at the pump and it sucks in more air when the oil is cold and thick and doesn't want to flow.

Have you changed the oil filter? What type do you use? Bypass the cooler by pulling the long hose back and putting it straight on the filter adapter.
paulh4

Nat put he uses Halfords Classic 20W-50 which a lot of old MG owners use and have no problems with, I've used it and it's fine.

As PaulW has note 20W is a range so can be nearer 20w or 29 (point nine recurring W and will vary as its additives wear.

Assuming the gauge is anywhere near right with its readings it seemed strange to me.

I like Paul4's idea of bypassing the cooler if only to show how much quicker the engine warms and pressure changes (and that you don't need a cooler on a standard B, just another go-faster stripes).

You would hope the garage put a new filter on when they refilled and hopefully changed the oil - but Nat put the pressure reading were about the same before the pipe burst and after. So you'd hope the taking a little while to get up to full oil pressure when starting from cold is just a wacky gauge or it does need investigating.
Nigel Atkins

On re-reading Nat's post it sounds more like the cold start issue is the filter's anti-drain not working properly, allowing the filter to empty when the engine is stopped a long time such as overnight. It then takes a disturbing number of seconds to refill before pressure cimes up. We have encountered this issue with far to many filters of varying brands in recent years.

Paul Walbran

I did wonder about the filter but that perhaps it was wrong type, but I took the takes a little while to get the pressure up as a good number of minutes rather than seconds but it was an assumption which is always dangerous. Perhaps fitting up a tester oil pressure gauge would give reassurance.
Nigel Atkins

A drained oil filter usually takes longer to _start_ registering pressure on the gauge, as with a new filter. I took this to be running long enough to start getting warm as in 'a few minutes' before registering full pressure.

Yes, first step with pressure issues is to try another gauge and line, and I'd also direct the line into a container and see what the flow is like in terms of volume, and also air bubbles, hot and cold.
paulh4

Don't worry nat, it was just a question on the cold oil pressure, it's most likely the filter or oil choice as PaulW says but just take it easy till the it gets warm and it'll be fine, maybe next oil change try a different brand oil filter and see what happens
It's a bit of a crazy system with the op relief valve early on in the system so any restriction from a blocked filter or thick oil causes the valve to blow off leaving a reduced flow out to the business end where it's needed
No big deal though, the oil pressure gauge is the last thing on the end of the oil supply and if you've got 45 dead cold there's oil everywhere there should be
William Revit

Nat,
If this exchange has persuaded you to inspect the bearings, you would be well advised to check the pump clearances.
FWIW I would run the car for another oil cycle knowing that it is possible run an engine without any oil at all when surfaces have first been coated with PTFE. From what you say, I suspect you will be hard pressed to detect excessive wear.
Keep us posted.
Roger Walker

It shouldn't be the Halfords (Comma) Classic 20w-50 oil unless it's some very dodgy stock or previous oil change(s) were poor quality partial cold drain(s) of generations of concoctions of gawd knows what and soup from the filter and cooler.
Nigel Atkins

ok, will keep you posted.

Roger - which clearances in the pump?

cheers
Nat

This thread was discussed between 20/02/2022 and 03/03/2022

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