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To say spark plugs will last 30,000 miles, 40,000 miles or whatever is absolute rubbish, even on a modern car. Mileage actually has little to do with it. There's a huge difference between 40,000 miles covered in a year to 40,000 miles covered in five years or ten years. Engines that clock up big mileage very quickly will be running at optimum temperature most of the time. And that will mean the engine will remain clean and well lubricated. Spark plugs should be replaced on a time basis more so than a mileage basis. It would pay to have a good understanding of how the high tension side of the ignition system works if you really want to know why changing the spark plugs is important.
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I haven't run a petrol car for over a decade - but when I did I used quad electrode types which lasted "for ever" - well, as long as I kept the car.
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To say spark plugs will last 30,000 miles, 40,000 miles or whatever is absolute rubbish, even on a modern car. Mileage actually has little to do with it.
I consider this statement to be 'absolute rubbish', as clearly mileage has everything to do with the life of a spark plug.
There's a huge difference between 40,000 miles covered in a year to 40,000 miles covered in five years or ten years.
What is the 'huge difference'? I presume it refers to the difference in the number of thermal shocks from cold to hot and back again experienced by the spark plug if the 40,000 miles is made up of two hundred journeys of 200 miles rather than a thousand journeys of forty miles, which should not unduly stress a modern spark plug.
..It would pay to have a good understanding of how the high tension side of the ignition system works if you really want to know why changing the spark plugs is important.
It's a pretty basic understanding and it leads me to contend that the passage of time is irrelevant.
This discussion has prompted me to inspect a spark plug in my TR7 this morning. My service record shows I last changed them in 1990 at 54,400 miles, and inspected them in 2008 at 64,000 miles. This morning, at 72,000 miles, the one I removed (Champion N12Y-C) looked fine with a still correct gap. I put it back, and left the other three undisturbed.
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To say spark plugs will last 30,000 miles, 40,000 miles or whatever is absolute rubbish, even on a modern car. Mileage actually has little to do with it.
I consider this statement to be 'absolute rubbish', as clearly mileage has everything to do with the life of a spark plug.
There's a huge difference between 40,000 miles covered in a year to 40,000 miles covered in five years or ten years.
What is the 'huge difference'? I presume it refers to the difference in the number of thermal shocks from cold to hot and back again experienced by the spark plug if the 40,000 miles is made up of two hundred journeys of 200 miles rather than a thousand journeys of forty miles, which should not unduly stress a modern spark plug.
..It would pay to have a good understanding of how the high tension side of the ignition system works if you really want to know why changing the spark plugs is important.
It's a pretty basic understanding and it leads me to contend that the passage of time is irrelevant.
This discussion has prompted me to inspect a spark plug in my TR7 this morning. My service record shows I last changed them in 1990 at 54,400 miles, and inspected them in 2008 at 64,000 miles. This morning, at 72,000 miles, the one I removed (Champion N12Y-C) looked fine with a still correct gap. I put it back, and left the other three undisturbed.
Then it's good that we can agree to differ. There is a lot to know about high tension ignition systems, just like there is everything else. And there's a lot more to a spark plug than it's initial appearance, which most DIY technicians wouldn't even give a thought to, and many garage technicians too for that matter. Not least that some systems use resistor spark plugs and some don't, and the reason why that is. And that's just the start. There's the plug firing voltage to consider, and the reason why the HT system is resistive. The wearing spark plug gap is just one of many reasons why they should be replaced. And time is equally if not more critical than mileage. If you leave yours in for as long as you have then good luck to you. You're very lucky to have got them out without shearing them or the threads in the cylinder head becoming damaged. And for the sake of a tenner for a set of plugs I know what I'd do.
Engines that do 'hot' miles will in almost every instance be in better condition than those that don't. It's said that 75% of engine wear occurs in the first five miles of every journey. And cold engines run richer when combustion is less efficient and carbon deposits accumulate more.
I could go on a lot more. Maybe another time. In the meantime I stand by what I say. Changing spark plugs, and other service items are more important on a time basis than mileage.
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To say spark plugs will last 30,000 miles, 40,000 miles or whatever is absolute rubbish, even on a modern car. Mileage actually has little to do with it.
I consider this statement to be 'absolute rubbish', as clearly mileage has everything to do with the life of a spark plug.
There is a lot to know about high tension ignition systems,..... Not least that some systems use resistor spark plugs and some don't, and the reason why that is.
That really isn't a 'lot to know'. Anyway, apart from the London to Brighton veteran run, I doubt if there is a car on the road with non-resistor plugs. Even my old TR7 has them......a 5 k ohm ceramic resistor to be precise.
All a spark plug does is to enable a brief pulse of sufficiently high voltage electricity to travel to its tip so it can jump the gap to earth and thus ignite the fuel/air mixture. If it fails to do this, either through leakage through internally cracked or otherwise faulty ceramic insulator or a ridiculously large gap between its terminals, then clearly it needs to be replaced. They are so well made these days that failure is rare and they will usually last well beyond the recommended change interval.
IMHO it is far more likely that HT leads or their connections will fail sooner than a spark plug, but AFAIK, no-one suggests inspecting or replacing these at a certain time/mileage interval.
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IMHO it is far more likely that HT leads or their connections will fail sooner than a spark plug, but AFAIK, no-one suggests inspecting or replacing these at a certain time/mileage interval.
The Focus we had never needed new HT leads in 12 years despite a set of plugs curing a slight hesitation/misfire after 4 years.
Plugs live in a pretty harsh environment, its a miracle they last 4 years IMHO. Back in my youth we would change them every 6 months. HT leads don't suffer as much and the quality of those is excellent these days.
Just looked on the web, a set of 4 Denso's for that Focus is about £11, less than I paid in about 2014. That works out at about 1.3 p per plug per week.
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The correct resistance, or close enough, is critical in the HT ignition system for the magnetic field in the coil to collapse at the right time and ensure the correct plug firing voltage. Too low and the spark will be released too early and will be weakened causing difficulty in starting from cold and will give rise to a misfire at higher engine speeds.
Too much resistance could cause the ignition coil to track internally as the spark seeks an alternative and shorter path to earth. This could even induce into the coil primary windings and voltage spike the ECM, which has happened quite commonly on Ford Fiesta and Focus models.
Often you can see brown burn marks at the base of the ceramic on the spark plugs. This will cause a misfire which will become more serious and expensive elsewhere if left unresolved.
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The correct resistance, or close enough, is critical in the HT ignition system for the magnetic field in the coil to collapse at the right time and ensure the correct plug firing voltage. Too low and the spark will be released too early and will be weakened causing difficulty in starting from cold and will give rise to a misfire at higher engine speeds.
Too much resistance could cause the ignition coil to track internally as the spark seeks an alternative and shorter path to earth. This could even induce into the coil primary windings and voltage spike the ECM, which has happened quite commonly on Ford Fiesta and Focus models.
Often you can see brown burn marks at the base of the ceramic on the spark plugs. This will cause a misfire which will become more serious and expensive elsewhere if left unresolved.
The brown stain or mark you are referring to is called coronal discharge and does not affect the functioning of a spark plug in any way.
drivcat.com/livedocs/1518.pdf
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Often you can see brown burn marks at the base of the ceramic on the spark plugs. This will cause a misfire which will become more serious and expensive elsewhere if left unresolved.
The brown stain or mark you are referring to is called coronal discharge and does not affect the functioning of a spark plug in any way.
drivcat.com/livedocs/1518.pdf
Well there's something I didn't know. To think of the number of spark plugs I've changed for that reason. Some have been to cure misfires though. I guess the brown staining was purely coincidental and that there was another problem with the plug or plugs which wasn't visible. Everyday's a school day as they say.
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In days of yore when mechanics were bold, wore dirty overalls and computers were for geeks, you had to diagnose engine problems using kit like this:-
probike.co.uk/diagnostics/electrical/ignitionmate-...r
I'm glad to see that it is still available.
It was very useful, it showed the relationship between LT voltage, spark voltage, plug gap and current. Plug voltage makes pretty sparks but plug current makes heat that fires the mixture etc.
That, a set of vacuum gauges and a Mercatronic coil tester were the main diagnostic tools back then.
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In days of yore when mechanics were bold, wore dirty overalls and computers were for geeks, you had to diagnose engine problems using kit like this:-
probike.co.uk/diagnostics/electrical/ignitionmate-...r
I'm glad to see that it is still available.
It was very useful, it showed the relationship between LT voltage, spark voltage, plug gap and current. Plug voltage makes pretty sparks but plug current makes heat that fires the mixture etc.
That, a set of vacuum gauges and a Mercatronic coil tester were the main diagnostic tools back then.
A vacuum gauge is still very useful today for diagnosing petrol engine faults. Every technician should have one in his toolbox. However different we may like to think modern engines are from their predecessors, the basic fundamentals and diagnostic techniques have not changed.
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probike.co.uk/diagnostics/electrical/ignitionmate-...r
That looks like a fancy multimeter. Cannot see any vacuum readings on the box or attachments for any vacuum pipes on a car.
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probike.co.uk/diagnostics/electrical/ignitionmate-...r
That looks like a fancy multimeter. Cannot see any vacuum readings on the box or attachments for any vacuum pipes on a car.
A multimeter is also still a very useful tool. The difficulty with it is actually being able to use probes to check circuits without damaging the wiring or terminal pins which are often very well protected and inaccessible. Technicians can often be led up the garden path using diagnostic equipment to check switches and sensors because they work on very low voltage or digital signals such as CANBUS. The controller can detect very low voltages and so a switch can be seen to be working normally even if the contacts are high resistance or slightly burnt. A voltmeter in a 12V circuit may show a difference of 0.00V across a switch when it's closed and for example 11.5V when it's open leading a technician to believe it's working properly, but the controller will still see a closed circuit even by 500mV . Moisture inside a switch very commonly causes this. The controller must see a zero voltage difference when the switch is closed, and full battery voltage difference when it's open otherwise it sees the same state. This is an example of course, but one that technicians often encounter.
I recently had a Ransomes Parkway 3 machine that would initiate the glow plug sequence and then crank itself and start when the ignition was merely switched on and the key not turned to start. On inspection the ignition switch had a live supply at Terminal 30, a live output at Terminal 15 when the ignition was switched on, and a live supply at Terminal 50 when the key was turned to the start position. This was checked with a conventional 12V test lamp. So what was the problem? The problem was the test lamp had a normal bulb which draws current. A small amount of moisture was present inside the switch. This was not enough to allow sufficient current to pass across the contacts to light the test lamp, but it was enough for the engine controller to detect a voltage and believe the operator had turned the key to the start position. I replaced the ignition switch and the problem was solved.
A conventional test lamp, an LED test lamp and a multimeter are all very useful tools and good diagnostic aids. But it's important to know which to use in each application and to understand what they're telling you. A multimeter does not know how to lie. It's giving you the correct information every time. If you suspect it's wrong or inaccurate then think again. It isn't. It's you who's not correctly interpreting what it's telling you.
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probike.co.uk/diagnostics/electrical/ignitionmate-...r
That looks like a fancy multimeter. Cannot see any vacuum readings on the box or attachments for any vacuum pipes on a car.
You seem to have misunderstood it's functions, it can monitor spark voltage + spark current + LT voltage or LT current - all at the same time on the bar graphs.
No vacuum functions on the Ignitionmate - they do a vacuum meter as a separate meter.
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No vacuum functions on the Ignitionmate - they do a vacuum meter as a separate meter.
I replied to Railroads post and not yours. That post seemed to suggest the link was to a combined unit that included a vacuum gauge.
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I have recently changed plugs at 50K miles on our 2012 Jazz.(10 years or 75k miles recommended)
The original NGK iridiums were fine with gaps in tolerance but the threads were starting to corrode. I replace them with Bosch iridium.
No noticeable change in performance or mpg.
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I have recently changed plugs at 50K miles on our 2012 Jazz.(10 years or 75k miles recommended).
With my 306's recent MoT I asked my indie to check and replace plugs if thought necessary. They did so, as although the plugs had only done 10K miles it had taken about 10 years (the car was off the road for 4 or 5 of those). They decided the age warranted it, and the cost is small anyway.
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I have recently changed plugs at 50K miles on our 2012 Jazz.
Dad had an early Jazz (for a short while), the one with the double spark engine thus 8 plugs. Took it to the local indy for a service who proved his vast knowledge by just replacing 4 of them. Dad took it back but the indy was adamant only 4 plugs needed replacing since the other set were simply there for emergencies.
Pretty sure on those early cars it was every 4 years for new plugs.
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I have recently changed plugs at 50K miles on our 2012 Jazz.
Dad had an early Jazz (for a short while), the one with the double spark engine thus 8 plugs. Took it to the local indy for a service who proved his vast knowledge by just replacing 4 of them. Dad took it back but the indy was adamant only 4 plugs needed replacing since the other set were simply there for emergencies.
Pretty sure on those early cars it was every 4 years for new plugs.
All eight have to be done but many don't , gaps wide with wear, and coil packs fail.
Numpties.
If buying a pre 2009 Jazz, check all 8 have been changed .Rear ones often ignored.
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I have recently changed plugs at 50K miles on our 2012 Jazz.
Dad had an early Jazz (for a short while), the one with the double spark engine thus 8 plugs. Took it to the local indy for a service who proved his vast knowledge by just replacing 4 of them. Dad took it back but the indy was adamant only 4 plugs needed replacing since the other set were simply there for emergencies.
Pretty sure on those early cars it was every 4 years for new plugs.
All eight have to be done but many don't , gaps wide with wear, and coil packs fail.
Numpties.
If buying a pre 2009 Jazz, check all 8 have been changed .Rear ones often ignored.
As you say all 8 have to be done as they both work, 2nd plug in cylinder fires on exhaust to reduce unburnt gases in the exhaust.
-other set were simply there for emergencies.- never heard that one before
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...... I asked my indie to check and replace plugs if thought necessary. They did so, as although the plugs had only done 10K miles it had taken about 10 years .....they decided the age warranted it, and the cost is small anyway.
They would, wouldn't they. Every little helps ;-)
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...... I asked my indie to check and replace plugs if thought necessary. They did so, as although the plugs had only done 10K miles it had taken about 10 years .....they decided the age warranted it, and the cost is small anyway.
They would, wouldn't they. Every little helps ;-)
No, I don't think they would, actually, John. They might have failed the car on a CV boot, but they passed it with an advisory. I've used them for a few years now and I know them quite well - in fact I have helped them to find some parts for old Peugeots ...
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I feel like a complete rebel. The 107 does about 5000 miles a year. I always like to check the gap annually so buy a set of 3 plugs for about £10, check the gap then simply drop the used plugs in the bin and fit the new plugs all in the space of a few minutes. I like to think this is giving the coil packs an easy ride and if I couldn't afford up to £10 PA, then I couldn't afford to run a car.
Quality spares are so inexpensive for this car that I like to know everything is in optimum condition at all times. Similarly I don't wait for water pumps to fail and my cars either have "new / newish" batteries or there will be a capacitor jump starter in the boot.
Blue Print discs and pads £49 etc etc
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I feel like a complete rebel. The 107 does about 5000 miles a year. I always like to check the gap annually so buy a set of 3 plugs for about £10, check the gap then simply drop the used plugs in the bin and fit the new plugs all in the space of a few minutes. I like to think this is giving the coil packs an easy ride and if I couldn't afford up to £10 PA, then I couldn't afford to run a car.
Quality spares are so inexpensive for this car that I like to know everything is in optimum condition at all times. Similarly I don't wait for water pumps to fail and my cars either have "new / newish" batteries or there will be a capacitor jump starter in the boot.
Blue Print discs and pads £49 etc etc
Out for a Sunday walk in the hills I came across a stream bank construction site which had just changed the Champion plugs on three small aircooled plant, so I picked the discards up put them back in the discarded new boxes, and put them in my pocket.
The car has NGK's in but these Champions seem to be compatible, so now I have spares.
Quality spares are so inexpensive for this car
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Out for a Sunday walk in the hills I came across a stream bank construction site which had just changed the Champion plugs on three small aircooled plant, so I picked the discards up put them back in the discarded new boxes, and put them in my pocket.
The car has NGK's in but these Champions seem to be compatible, so now I have spares.
Quality spares are so inexpensive for this car
Tommy Robb, the motorcycle racer, relates a story in his book from the Isle of Man TT races in the early 60s. He was practising for the 250cc TT on his factory Yamaha, and being more used to 4-stroke engines he was having a little difficulty getting to grips with using the air lever, which needed to be used to compensate for altitude changes around the course (highly-tuned 2-strokes being notoriously fickle about mixture strength).
As he was climbing the mountain, he forgot to close the air lever which meant he oiled the plugs and the bike died. Looking around he saw a tractor in a field, so he leant the bike against the hedge, borrowed a plug spanner from a nearby spectator and took two plugs out of the tractor. By coincidence the tractor's plugs were the same thread and reach as those in the Yamaha, so he fitted them, and the bike fired up. He was able to tour back to the pits, saving a long wait or a long push.
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With the increasingly bad Covid outlook (again) it looks pretty unlikely we will be changing the Pulsar anytime soon so since its 4th birthday is in February it will be time to treat it to a new set of plugs.
Been on E-Bay and had a shock. Top of the list was NGK at £100 a set, fell off the chair. Next was a set of that well known brand Pulstar (not a spelling mistake - anyone heard of them) at £63.96 a set. Thought things were looking up when I found a seller with Denso at £14.56 but its only for one and he only has 2, very useful. More searching found Bosch at £45.31 a set but eventually found a seller doing Denso at £11.61 each and he has over 10 in stock. So that £46.44 a set. Will check the local factors next week but I doubt they will beat that.
Last time I bought plugs for the Focus 1.8 they were nowhere near that much so I looked at the price for Denso, £11.87 for a set of 4 posted, under a tenner a set if I bought 3 sets..
Why would plugs for a Nissan be 4 times the price I wonder?
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.Why would plugs for a Nissan be 4 times the price I wonder?
If you know the specific NGK plugs needed, try sparkplugs.co.uk, I've bought from them for ages and they're always reliable and competitive on price.
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Ever thought of writing a blog, Ed? "Tinkering in Taiwan", or some such?
I'd certainly subscribe!
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If you know the specific NGK plugs needed, try sparkplugs.co.uk, I've bought from them for ages and they're always reliable and competitive on price.
Thanks for the link, just had a look.
For the Pulsar they only list NGK at £15.78 a plug which is not only more expensive than the Denso's on e-bay but they have no stock.
Whilst on I looked at the Focus plugs, Denso @ £2.48 each so slightly cheaper than e-bay and in stock (obviously don't need them, don't have the car now) but these prices are plus postage which will probably make them more expensive.
I used either Bosch or NGK plugs for years and after the rubbish plugs we got for British cars in the 70's and into the 80's they were a revelation, never needed adjusting or cleaning and never seemed to cause issues. But the NGK's I bought for the Focus (the correct ones) caused an immediate issue. The plugs leads were supposed to seal into the cam cover but they stood proud by about 1/4", when I compared one against the Ford original they were about 1/4" longer from the seat to the connector. Took them back and the chap agreed and refunded me. Went to specialist Ford factors who recommended Denso (he only sold them and the Ford originals) and when he showed me one against the Ford plug they were identical. Used then ever since.
Still a bit nervous with NGK's after that experience.
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There used to be a member on here years ago called THe Growler (RIP) who did various ramblings of the motoring scene in the Philippines.
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