S80: Engine Spark plug specification and lifespan- A write up!

[Nogbad the Bad]

Hi All
I wanted to share my experience of spark plugs for my Volvo S80 1999 2.4 petrol non turbo.

When coming to replace the plugs, I read a number of posts warning against using anything other than the Volvo branded items. I disagreed with this approach; Volvo don't manufacture their own plugs, so it was a matter of tracking down suitable alternatives.

I replaced the Volvo plugs after 45,200 miles (see photo). Volvo plug v3.jpgWay beyond the 30,000 miles recommended and completely worn out. I had simply forgotten about them until one day I noticed a slight hesitancy on the motorway that came and went a couple of times.

I replaced them with NGK BKR6ETUC plugs. The part that sticks into the combustion chamber is both longer and fatter than the Volvo originals, and I was worried about the plug hitting the piston. However, that didn't happen. Once replaced, I noticed the engine had a slightly different tone to it, which I attributed to a slightly raised compression ratio. Aside from this, I noticed no change in performance or economy.

I replaced the NGK's after 46,250 miles (photo). NGK plug v2.jpgAs you can see, they actually lasted better than the Volvo ones, and I feel still have a bit of life left in them. The replacement wasn't driven by any change in engine performance, but I have noticed in the last few weeks a slight drop off in economy.

This time around, I've used Denso K20PBR-S10 (photo). Denso plug v2.jpgAs you will note, very similar to the Volvo originals apart from the height of the shoulder on the nut.

Both the NGK and Denso parts are the recommended ones in their respective parts catalogs for the 2.4 engine.

So in summary, there are perfectly good alternatives to Volvo spark plugs, that last at least as long at less than half the price. I would recommend replacement at 40,000 miles, a little longer if money is tight.

I trust you've found my write up useful.

[Tatsfield]

For the benefit of others reading this thread I would offer some information on spark plugs against which to consider the OP's interesting post.

Firstly that the enemy of the spark plug is its own child, the spark that it generates. When a high voltage spark arcs across a gap in produces intense heat which burns the contacts as it passes. Since the size and timing of the spark is, in part, controlled by the size of the gap between the side and central electrodes, any change in this gap will effect the spark formation and that will effect the timing and strength of the spark which has to ignite the fuel/air mixture. So, as a plug is used and ages, the spark gap increases. Back in the bad old days, mechanics would routinely remove single electrode plugs to measure the spark gap and reset it to the specified gap.

Spark plug manufacturers adopted two game plans to reduce the effects of spark erosion on electrodes. Firstly they increased the number of side electrodes. This design development started in the aircraft engine industry where a failed plug could bring down a plane and where there was a constant pressure to increase the time between engine maintenance. Despite what many believe, the purpose of multiple electrodes is not to deliver multiple sparks. Sparks will always choose the shortest route and so with multiple electrodes there will only be one spark which uses the narrowest gap until erosion increases the gap and the current chooses a new shortest path and this continues to wear back the electrodes but unlike a single electrode, the rate of erosion is shared between several points and the time when there are no suitably narrow gaps left is delayed. The second ploy is to make the electrodes from material which is less prone to spark erosion without adversely reducing the quality of the spark by passing it through a material which may not conduct adequately.

So you can see that spark plug design is a complicated activity and choosing the right plug is not as easy as trusting the brand and being swayed by the advertising. A plug which performs well in one engine design might not be as effective in a different one. I owned a particular car where the model changes over the years increased the spark plug change interval from between 24 to 40K to between 48 to 80K because the associated work entailed in changing the plugs was being carried out at longer intervals. To achieve this, the plugs on the later engines were re-specified to ones which lasted longer and the coil system was changed to minimise erosion.

So before opting for a different plug to that specified by Volvo, it is imperative that you research exactly which plugs are truly compatible with the engine.

Me? I run a diesel!

[Boatie]

Oh for the days of Champion plugs at 5/- a pop (25p) or cheapie Wipec ones at 3/9 (19p).

Frank
V90 D5 R Design (oil burner)

[Ian21401]

Originally Posted by Boatie

Oh for the days of Champion plugs at 5/- a pop (25p) or cheapie Wipec ones at 3/9 (19p).

Frank
V90 D5 R Design (oil burner)

Once upon a time, 4 Champion plugs and a set of contact breaker points for £1.00. But had to be changed every 6,000 miles, the points were cheap rubbish so binned them, and only earning peanuts anyway.
Only way to measure it is how many hours of work needed to earn the cost of the item in question. I could buy 10 Senior Service tipped for 1/11d. (10 new pence) but I was only earning £5.00 per week.