When to change spark plugs - relatively high-spec engine

When to change spark plugs - relatively high-spec engine

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Kent Border Kenny

Original Poster:

438 posts

16 months

Friday 26th June
quotequote all
I’ve a first generation R8 Plus. It’s done only 22,000 miles, but is six years old, so the service schedule says it’s time to change the plugs.

I’ve not come across the idea of plugs having a life in years before, only mikes, so I’m not sure why they’d need to be replaced, but I’m also not keen to play around with a 5.2 liter normally aspirated V10 engine that revs to 8,000 and outs out 540bhp. Maybe a plug failing would do no harm, maybe the unmatched forces would end up shaking some very important pieces loose before I notice anything.

Does anyone have any idea if there’s any point changing them? I will if here’s any reason at all, but won’t if they are going to be as good today as the day they were installed, as I prefer to leave alone if nothing needs doing.

kambites

59,495 posts

177 months

Friday 26th June
quotequote all
I've never heard of a failing spark plug damaging an engine except where the plug has actually disintegrated and dropped a piece of metal or ceramic into the cylinder and I've never even heard of that happening in a modern engine. As long as the mixture is accurately controlled (which on a modern direct injection engine it damned well should be) spark plugs last a very long time and their failure mode is just to gradually wear away their electrodes so the spark gets weaker which will manifest as a slight misfire. If you left it misfiring for too long you might damage the cats, but it shouldn't hurt the engine as such.

On the other hand, replacing the spark plugs is presumably not hugely difficult and hence not particularly expensive? So on a car of that value is there a good reason not to follow the manufacturer's advice? Or is it an engine out job or something daft? If nothing else, failing to stick to the manufacturer defined service schedule won't do its resale values any favour.

Edited by kambites on Friday 26th June 19:20

SidewaysSi

7,488 posts

190 months

Friday 26th June
quotequote all
How much are we talking about? Is it really worth skimping on a car of that value?

deggles

357 posts

158 months

Friday 26th June
quotequote all
How accessible are they? Might be worth just pulling a couple of plugs out for a visual/gap check before deciding to replace?

Kent Border Kenny

Original Poster:

438 posts

16 months

Friday 26th June
quotequote all
SidewaysSi said:
How much are we talking about? Is it really worth skimping on a car of that value?
£400, they are expensive, there’s ten of them, and I’m more than likely to manage to scuff the carbon fibre in the engine bay if I do it myself.

As I say, if there’s any reason at all that they do need a change based on years then I’ll do it, but if it’s just Audi harping their franchises with some unnecessary work then I won’t.

SidewaysSi

7,488 posts

190 months

Friday 26th June
quotequote all
Kent Border Kenny said:
SidewaysSi said:
How much are we talking about? Is it really worth skimping on a car of that value?
£400, they are expensive, there’s ten of them, and I’m more than likely to manage to scuff the carbon fibre in the engine bay if I do it myself.

As I say, if there’s any reason at all that they do need a change based on years then I’ll do it, but if it’s just Audi harping their franchises with some unnecessary work then I won’t.
Ring up an Audi specialist?

Kent Border Kenny

Original Poster:

438 posts

16 months

Friday 26th June
quotequote all
SidewaysSi said:
Ring up an Audi specialist?
Yes, probably the best idea. The plugs on euro car parts range from £14-24, so £140 to £240 for the set.

g3org3y

15,350 posts

147 months

Friday 26th June
quotequote all
Is this a car you're planning on keeping?

For prospective buyers, deviation from the service schedule may raise eyebrows.

Dogwatch

5,442 posts

178 months

Friday 26th June
quotequote all
Kent Border Kenny said:
£400, they are expensive, there’s ten of them, and I’m more than likely to manage to scuff the carbon fibre in the engine bay if I do it myself.

As I say, if there’s any reason at all that they do need a change based on years then I’ll do it, but if it’s just Audi harping their franchises with some unnecessary work then I won’t.
yikes

Spark plugs wear out with use. Being just metal and ceramic they aren't particularly time sensitive.

rockin

8,113 posts

201 months

Friday 26th June
quotequote all
Dogwatch said:
Spark plugs wear out with use. Being just metal and ceramic they aren't particularly time sensitive.
Yes, and that's exactly the point. Age doesn't matter much (so long as the the threads don't get stuck) and mileage doesn't matter much so long as the car hasn't got humungous engine hours as a result of churning away at 10 mph in stop-start city traffic.

As with all maintenance the manufacturer recommendations are based on "average" use. If your use is kinder to the car you can extend intervals a bit. I certainly do.

kambites

59,495 posts

177 months

Friday 26th June
quotequote all
rockin said:
As with all maintenance the manufacturer recommendations are based on "average" use. If your use is kinder to the car you can extend intervals a bit. I certainly do.
I think they're generally based on worst-case (or at least worst few percentile of cases) use rather than average because manufacturers don't want to pay out for warranty claims and do want people spending money at their franchised dealers.

NMNeil

396 posts

6 months

Friday 26th June
quotequote all
kambites said:
I've never heard of a failing spark plug damaging an engine except where the plug has actually disintegrated and dropped a piece of metal or ceramic into the cylinder and I've never even heard of that happening in a modern engine. As long as the mixture is accurately controlled (which on a modern direct injection engine it damned well should be) spark plugs last a very long time and their failure mode is just to gradually wear away their electrodes so the spark gets weaker which will manifest as a slight misfire. If you left it misfiring for too long you might damage the cats, but it shouldn't hurt the engine as such.
It's a known problem in the Ford Duratec DOHC engines.
The plugs are a sod to change as it involves removing the upper intake manifold, so many people don't bother and exceed the miles before changing the plugs.
As the plugs wear the gap widens and it takes more energy to get the spark to jump the gap. This extra energy is dissipated in the winding's of the coils and they overheat causing the internal insulation to break down. When this happens it overloads the IGBT's inside the PCM and they fry.
When I checked my coils under a magnifying glass 4 of them had hairline cracks across the potting compound and the plug gap was wide enough to drive a bus through.
So by not changing the plugs on time I paid for 6 new ignition coils and a rebuilt PCM, and of course 6 new plugs.

Voice of experience, change the plugs at the recommended mileage.


bgunn

977 posts

87 months

Friday 26th June
quotequote all
Other thing to bear in mind with leaving very long plug change intervals is that they frequently seize into the head if left for *very* long lengths of time (not miles).

Change them.

stevieturbo

14,879 posts

203 months

Friday 26th June
quotequote all
Often manufacturers service schedules are a maximum...even if most main dealers ignore things yet charge you for them.

But the real question is....why would you not change them ?

You would never leave plugs beyond their mileage life....if anything I'd change well before. And as metals are also used in plugs, sitting idle for long periods, corrosion could be an issue depending on the environment.

Just change them

NMNeil

396 posts

6 months

Friday 26th June
quotequote all
bgunn said:
Other thing to bear in mind with leaving very long plug change intervals is that they frequently seize into the head if left for *very* long lengths of time (not miles).

Change them.
Anti seize every time, especially with aluminum heads.

Evoluzione

3,945 posts

199 months

Saturday 27th June
quotequote all
My personal preference with plugs is that they do a heck of a lot of mileage before being problematic, when they start to cause misfires or poor running then change them, changing them early is a waste of time and money.

Cornwall1

30 posts

10 months

Saturday 27th June
quotequote all
I own an Aston Martin and they use mileage, first plug change is 70k.

I would take one out check condition put back in if it looks okay and carry on.


Boosted LS1

19,115 posts

216 months

Saturday 27th June
quotequote all
NMNeil said:
bgunn said:
Other thing to bear in mind with leaving very long plug change intervals is that they frequently seize into the head if left for *very* long lengths of time (not miles).

Change them.
Anti seize every time, especially with aluminum heads.
Not so. It depends on the plug. You need to have a good earth.

Pan Pan Pan

6,353 posts

67 months

Sunday 28th June
quotequote all
If you intend to sell the car on, then having a full service record which includes having the plugs changed at the vehicle manufacturers recommended interval, might be worth while.
It may also be worth contacting the plug manufacture for their opinion on changing the (expensive) plugs at what might seem like a very short interval.
Some people like to fiddle with cars, (whether they need fiddling with, or not) whilst others adopt an `If it aint broke, then FFS don't fix it attitude'
Plug manufacturers might be ambivalent about this. because by changing plugs at low mileage intervals, they get to sell more plugs. Conversely, they might get a bit worried if it gets widely known, that `their. plugs don't last properly beyond a few thousand miles.
Many manufacturers usually want people to know how durable and `long' lasting their products are. So it may actually be possible to get an objective view from the plug manufacturer.

PositronicRay

19,249 posts

139 months

Sunday 28th June
quotequote all
I would change them, Audi FSI engines over fuel like crazy before they're properly warm. Kills the plugs.