Well I hate to admit it but I was wrong about some types of sparkplugs. When I bought my 240 the first thing I did was tune it up, installing new wires, cap, rotor, and PLATINUM tip sparkplugs. It ran ok when I bought it and ran better after the tune up. Still it seemed to have more of a swing in idle speed that I would expect and seemed to be weak on acceleration. I wrote off the lack of hp to the normal volvo engine performance.

In the past I would have said all sparkplugs are the same and only went with the Platinums for longevity. The other day the old girl seemed a bit sluggish after only 30,000 on the tune up. So, I decided to change the plugs. This time I decided I would go with NGK copper plugs instead of Platinums. I pulled the plugs and they were all clean, normal color, and normal gap. In short, all in great condition. After putting in the copper plugs BOY!, was I surprised! The engine settled down to a very smooth idle, much more so that when I first tuned the engine. It accels better now, more power, in short the engine is just simply running better on the copper tips than the platinums.

I still cannot explain why this is so, but for volvo engines I will no longer use platinum tip plugs.

Well, i've been using them for about a year now, but only 5k miles, in my 74 b20f engined 68 142... Later today we'll be taking out the platinums, taking note of their condition and gap, and then putting in some NGK coppers as their replacement... If I notice an improvement(probably will, my car's been giving me some problems of late...), I will be greatly happy and of course post my results. I haven't seen them since i first put them in, so we'll see what they look like.
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Kyle - attending Ore. State, while my lil '68 142 (256k, 74 b20, m40, iPd bars, other misc... =D) waits for its next outing... (My Cardomain site)

Out they came today, and they looked to be in great shape. They were still gapped correctly and didn't appear to be fouled or anything. As far as the car running better, well, i'm not so sure, it might, but it might not. We messed with some other stuff on the car as well, and the carb actually started working even worse than it has been, so i don't really know if it's any better. But I'm hearing here that the platinums require more power to have the same power of spark, and my car's ignition system is nothing special really, so i'd rather have the better spark than whatever plus there was to having the platinums in there. But if i ever have some plugs strand me, i can just pop the platinums in there and call it good until i find some replacements.
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Kyle - attending Ore. State, while my lil '68 142 (256k, 74 b20, m40, iPd bars, other misc... =D) waits for its next outing... (My Cardomain site)

I started using NGK coppers in my very first car, a 122S, when I bought it in 1974. I have wound NGK into every car I have owned since.
I have tried the early Bosch platinums. I won't try them, or any other brand again, in any car more than a few years old.
The purpose of platinum and other rare metal electrode plugs, is to extend the service interval, useful when the plug is nearly impossible to get at. What is not revealed is that the platinum and iridium plugs require a higher firing voltage, and although very new cars can produce these voltages with reserve, older cars cannot, or are operating near the voltage limit.
I prefer to read the plugs occasionally too, to see how things are going in the combustion chamber. Even some car manufacturers who install long life plugs advise that they be removed and "inspected" at shorter intervals than they are replaced, both to confirm the engines operating behaviour and to ensure the plug doesn't weld itself into the head. The incidence of broken plugs and damaged threads is on the increase - many cylinder heads are rebuilt for this reason.
So NGK plugs, a bit of Never-seeze, and yearly replacements work for me. On an engine like the B21-23-230, there is really no excuse for not yanking the plugs out yearly, as they are about the easiest engine ever for plug access.

I have to agree with you on removing plugs and at least putting antiseize compound on modern aluminum head engines. We have a real problem with Ford 4.6 and 5.4 and the 10 cyl engines blowing out sparkplugs occasionally. In most cases the head has to be replaced instead of retapping.

I wasnt aware of the higher resistance of the platinum plugs. Thanks for the info. I have always believed in using metal plug wires instead of carbon for the lower resistance. The monomag wires are great for this and no radio interference. Been using them for years.

If you like to experiment, next time try Denso or NGK iridium plugs. jp

For some reason..."secondary resistance" (sounds like a battle front).....Bricks seem to react better to non platinum plugs. Better everything with the cooper cores.

Also, a basic.......the gray coloured dizzy caps, or those with aluminum terminals.........unless you enjoy pings, backfires, slow everything, and love spending money on gas, stay away from them. I let my parts guy con me into one.......he's still my parts guy, but now knows better.
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84, 242GLTi, 167K, 4+OD, in rehab; 89, 245 DL, 252K, M 47, daily driver; 93, 245, auto, 167K ; and other toys.

was told to beware of platinums made in india, was also told fuel consumption would increase, ill stick with ngk's

When our 83 was much newer I was experiencing hard starts some winter mornings and had it scoped at the dealer. The comment on the tech's work order read "High secondary resistance - car has platinum plugs". The service mgr said "tsk, tsk".

That ended my experiment with the Bosch platinums, and for the last dozen plus years and 100k, she's run fine on NGK BP6ES copper plugs. At the latest 30k changeout, they looked a little wide and checking showed gaps around .035-040. Guess I'll shorten the interval.
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Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, 'my' 94-944 B230FD; plus grocery-getter Dodge minivan, hobbycar MGB, and numerous old motorcycles)

Funny thing about plug gaps. Platinum plugs are labelled "Do not adjust gap". The regular copper cores can be regapped at your pleasure. I found that if I regapped every 7-10 thousand miles I got great results, kept the plugs for lots longer than 30k.
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01 V70 2.4 M5

I have not noticed any problem whatsoever in turbo and non-turbo cars for 5 years or so. Other than the higher cost.

Funny, I have had the same experience with two 240DL's a 740GL and a S70GLT. No more Bosch Platinums for me. From now on only Copper core NGK's.