2004 XC70 -- Spark Plugs; Denso Iridiums?

[oragex]

Change interval is long especially on turbo engine, however a quick check is not a bad idea for two reasons: first it will make sure the plug doesn't get stuck if left in there for too many years, and second, a worn plug will cause additional stress on the ignition coils and may cause some of them to fail. Speaking of coils, after being there, it is a good idea to keep a spare one with 1-2 wrenches inside the trunk, it will surely fail away from home (Murphy's law) and driving the car with a failed coil is not a good idea (at least unplug the corresponding injector and don't drive uphill)

[Rattnalle]

I'm thinking higher fuel standards might contribute to less plug wear over here which in turn might be why failing coils isn't a common point of discussion on Swedish forums (fora, for you Latin lovers in the young new world).

[June]

I'm thinking higher fuel standards might contribute to less plug wear over here which in turn might be why failing coils isn't a common point of discussion on Swedish forums (fora, for you Latin lovers in the young new world).

Also from what I understand plug gap widens with mileage, wider gap = higher resistance to create the spark. Eventually too much resistance opens the coil. I understand spark plugs act as a resistor does in electronics. Change the value and burn out the component. Hince the Blue Box plugs start out their life as the intended resistance and during the 60K per my car's maintenance schedule remain within acceptable tolerance for reliability of coils. I am quite sure Volvo thoroughly tested plugs/mileage before creating the maintenance schedule. I wonder if non Blue Box plugs may have different resistance values to begin with? Possibly causing misfires that so many posts here on MVS when some aftermarket plugs are used? Just my thoughts on the subject.

On a earlier post you mentioned the components I listed are not wear items. I understand a misfiring engine can damage the O2 sensors and catalytic converters. Worn or incorrect plugs can cause coil failure.

My car having appropriate services preformed at the correct intervals with Blue Box parts has given me years of reliable service with my car. Personally I don't see any financial hardship with the cost of the two sets of plugs used in my car thus far. Especially since the car has run flawlessly the entire time. In fact I noticed no change running wise of the engine either time the plugs were changed.

What really effects the running of my car is the octane and quality of the fuel. Here in the United States Shell premium 93 octane is the best, and almost exclusively what I use. My car loved back when Shell offered 95 octane as Super Premium at certain stations. Sadly Shell did away with 95 octane fuel years ago. It seems Shell premium has the highest detergent content. Perhaps the higher detergent content has kept my injection and cylinders cleaner? Adding to the life of the components? June

[abscate]

Once I got to the trouble to remove them, Im going to put new ones in - I guess thats why I also stay away from 100k rated ones. I will sell the old ones as tested spares to a Scot somewhere....and close the deal with tested engine oil as a free add-on

[mrbrian200]

For plugs on turbo cars I'd be cautious about using anything other than OE without a tune.