I, too, have heard nagging doubts about Bosch Platinum plugs, but I am a true believer when it comes to my 854T. For my car they work best longest. I know nothing beats a trial like a failure, and I haven't tried many plugs, but I know they work better than the std OEM plugs ever did and they stay that way for at least 30K miles. I just pulled my 3rd set after 40K miles. The new set is, of course, a bit crisper, but I had no problems with the prev set @ 40K mi! They were down about 1.4% in combustion efficiency, based upon my cruise rating system, in which I add avg mph with avg mpg for long cruises.

I just had my car's emissions tested today, 3rd time, and these are the best readings yet (see this post).

So if your engine is in perfect operating condition, the BPs should behave in a superior fashion, as recommended by Bosch, the designer+maker of your car's ignition system.

In (nearly?) all other plug designs, both electrodes become rounded over time, especially at elevated temps as in a well-exercised turbocharged engine. This raises firing voltage requirements and usually results in occasional misfires, which leads to dirtier combustion chambers, and the whole combustion process devolves downhill from "laboratory conditions". Only(?) Bosch Platinum completely protects the center electrode from rounding. So hard use doesn't age them at anything like what happens to (all?) other plugs. They also claim to get up to self-cleaning temps faster than other plugs. BTW, I 'never' (well, almost never) make brief trips in my car unless it's already up to temp. This also helps keep the plugs clean and thus firing well consistently.

I therefore suspect that cars which tend to misfire or otherwise expose the plugs to anomalous combustion chamber conditions (older cars with manual chokes, which could see overly-rich mixtures at times are a prime suspected cluprit) may not experience the same greatness from Bosch Platinums as I have in my car. BTW, I tried to melt the first set by not properly/fully tightening them, which led to leaner mixtures and hotter temps, but the BPs withstood the torture very well (click for pix). I've also exposed them to extreme extended high-boost conditions (running hard uphill switchbacks for 20 miles at altitude) and they shrugged it off. Similar conditions could wear out a set of NGKs in a hard/fun morning or two in my previous turbocharged car.

I've long maintained that my car experiences superior combustion efficiency in its engine (Bosch Platinums help, as do the DurAlt 'vitamins' with which I treat the gasoline), and today's emission test (with 3.7K mi on this set of BPs) seems to verify it.

When the recommended-by-the-manufacturer/designer premium plug works so ideally for so long (in my car, anyway) at $2 apiece (the current good street price), why screw around with anything else?

0.7mm = 0.028" and I recommend you more-or-less fully coat the threads thinly with anti-seize compound. And the *hot* davespeed tip: the screw-on top connector will tend to come loose (unscrew ever so slightly) during the 30K mi recommended interval. So unscrew it completely (remove it), and take some diagonal cutters or other tool of destruction and lightly crunch the now-exposed threads on the top of the plug. When done correctly, the top connector will still screw on but with increased torque/friction that will ensure a better (optimum) connection longer ('forever') once fully tightened.

In case you try the Bosch Platinums and for whatever reason you don't like them, I believe Bosch still offers a money-back guarantee (http://www.boschusa.com/AutoParts/SparkPlugs/Platinum/ has a "performance guarantee form", but I didn't follow that link).

- Dave; '95 854T, 143K mi; K+N, DurAlt, Mobil1, Bosch Platinums

Hey- I recently went round and round with this subject, and ended up just paying the $32 for 'volvo' plugs. They are actually Bosch plugs, but they are different than what you can get at the parts store, or so I was told. They are a copper core, with a platinum coating. I had actually bought a set of Bosch platinums before I got the volvo plugs for $10. The plugs were different, though- the 'bottom' of the gap was porcelain out side, with the electrode pickup inside, concealed. I talked to a friend that works at volvo, (he has given a lot of good info, and doesn't try to just sell volvo stuff to me) and he recommended bhuying the volvo plugs there. I figured, what the heck they're more expensive, but they'll be in there a while. I didn't want to chance it with a different temp plug that may lower performance, or run too hot or cold. Hope this helps.