Does anyone here understand spark plugs?

First of all this is for a 2.5L Turbo petrol Volvo S40 (T5 or more likely to be known as the engine in the Focus ST)

Looking at changing the plugs, which according to the NGK site I need a ILFR6B. The usual plug for these cars seems to be of the iridium variety.

These plugs are £10+ each, however one of my local motor shops has ILFR6C plugs, which are normal non-iridum ones and they cost £3.95 each. Which I have bought and was going to fit, but I'm a bit OCD with these things and would not be able to live with myself knowing they aren't quite right. Their books tell them that the car can use these too.

So my questions are, will the lack of iridium make a difference and what is the difference between the last letter, B+C.....

Any info is much appreciated

Thanks.

[Bibio]

as far as i can remember its to do with service life. iridium will last 4 times longer than normal copper. same applies to fully synthetic oil.

i have seen copper last megga miles though. good fuelling and ignition system will make plugs last longer.

What he said!

[BanannaMan]

In older cars service life might be the main difference but in most newer cars that call for iridium spark plugs, you're likely to have running problems as well.
Slow starting, poor idling, cutting off at idle, hesitation or stumble during accelleration are the most common problems.
Don't waste your money on inferior parts.

[NTECUK]

http://www.sparkplugs.co.uk/pages/te...park-plugs.htm

These new cheaper ones are Nickel core, the ones I pulled out are Bosch Platinum. So appart from melting point these ones are much better than the platinum? So it may even be an improvement?

Many thanks.

[Mauler]

If it was running fine then I'd put in the same as what came out, otherwise go for what the book says.

[embee]

I'd start with the question "why do you want to change the plugs?"

Iridium or platinum etc types will last a lot longer than most service intervals suggest, many applications have 100k mile change intervals for double precious metal designs (tip and ground electrode). Unless you're driving it particularly hard (and I can't see how many peiople could possibly drive that engine really hard for long on UK roads) they'll usually be good for 50k miles minimum.

If it's starting and running fine then leave the originals in, unless you have a particular reason to change them.

Providing the heat range is appropriate and the basic design is equivalent (projected length, resistor etc) then it should be "safe" to go with a non-iridium/platinum design. There could potentially be some combustion stability issues but I doubt anything of any great consequence. Don't get hung up on things like "nickel" or "copper core", practically all modern known-brand plugs have nickel parts and copper cores to centre and ground electrodes to conduct heat away to the body. In a precious metal design it is only the very small tip which is special, it's a short "wire" insert in a "conventional" nickel support or similar (minimum material due to cost). They won't last anywhere near as long as the platinum ones though, tip erosion being the usual mechanism.

Hi,

Spark plug interval is 70k, car is currently at 81k. Also I find that occasionally there is a slight shake in the idle. Car doesnt throw up any error codes so I think this is worth a try!

I should be picking up a set of iridium ones today after work, cost a lot more but Id rather it got the ones defined by NGK and Volvo! Didnt fit the cheapo ones luckily so I can bring them back!

I doubt I will own the car long enough to see any type of spark plug wear out anyway, theres only so long Ill be able to stick the 26mpg!

Thanks for getting back to me!

[embee]

Well at 81k I think you've had your money's worth out of them, so I reckon you're doing the right thing. Try to rationalise it in terms of cost of fuel (in the parish of 13000 litres used, and the plugs are how much? )