Here is what worn BOSCHWR7DP looks like under the microscope.
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When I talked to someone at Bosch, I was told not to use platinum plugs in turbocharged engine. Here is a pix of the insulator failure. The insulator broke and almost feel out if it was not for the symmetrical arrangement of three ground electrodes that caught it. I would sure hate to see a chunk of ceramic like this blowing through my turbo.
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The plug is from a five cylinder Volvo. I do not think that it was a turbo PN
205 x 9146775 Made In France. Is that kind of failure common?
Another interesting failure is that of the internal resistor. A good resistor plug will measure about 4 to 7 thousand ohms between the tip and the HV connector. This series resistor often fails and although the plug will likely still fire now he have a situation where spark has to occur in three different places simultaneously assuming that the car has a distributor. Behaving strangely under load?
There was a link to a NGK website earlier in this thread. If you go to that link you'll see the explanation of why a dual ground tip plug is used and the difference in configuration between it and a "normal" plug. Contrary to those who keep telling you that you are wrong in wanting to use these plugs and that the dealer is lying to you, to me it looks like the dealer is correct. As the NGS link explains, having two ground electrodes doesn't mean they both fire at the same time, it means that plug life is extended because that style of design experiences greater ground electrode erosion. If they only had one ground electrode the plug would not last the desired length of time before erosion made the gap too large.
I don't know what it is about the toyota engine that causes them to want that particular style of plug but different combustion chamber designs can have different swirl patterns of the air fuel mix, some wind up "stratified", etc. They presumable have found that for the combustion chamber in that engine they need the exposed spark face they get from the dual ground plug rather then the shrouded spark you get from a "normal" plug.
I recommend you stick with what your manual calls for despite the scoffs from the various "experts" on here.
Here is the quote from NGKs website
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click on "multi-ground" on the left side of the webpage.
Multi-ground
Some combustion chamber designs (such as a rotary motor) require that the spark plugs have the ground electrode placed to the side of the center electrode rather than below as on a traditional plug (see photo). This firing tip design tends to erode the tip of the ground electrode faster than a traditional plug, erosion at these points creates a larger gap between the center and ground electrodes causing plug misfire. Thus by having more ground electrodes you extend plug life. It is important to note that multi-ground does not mean multi-spark, there will still only be one spark at a time. Therefore a multi-ground plug will not perform any better and may actually perform worse than a traditional plug, unless the engine is designed for a multiple ground plug.
AZGuy wrote: I recommend you stick with what your manual calls for despite the
i should mention i don't think the 'experts' were saying to stay away from the multiground plug, but rather, to stay away from the bosch plug, (which through experience i have found does not work very well with toyota engines). that's what i got out of it anyway.
volvo engines call for a 3 electrode plug. same thing here, the OE style plug works great, but not the bosch platinum plus2 or plus4. go figure.
i always suggest customers go with the OE style plug called for in the manual
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