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In 1999, Robert Bosch Corporation introduced a new breed of premium spark plug called the "Platinum +4." The new long life plugs, which retail for around $6 each, have a unique four pole electrode design that eliminates wear, resists fouling and improves ignition performance over a wide range of operating conditions.

Surrounding the center electrode, which contains 75% more platinum than previous Bosch platinum plugs, are four "surface air gap" ground electrodes made of a special wear-resistant nickel yttrium alloy. The angle and position of the four electrodes creates multiple spark paths that cause the spark to jump sideways. This has a self-cleaning effect on the center electrode and results in a longer, more powerful spark that reduces misfires for improved engine performance, better fuel economy, lower emissions and faster acceleration.

When these spark plugs fire, the spark jumps randomly to any one of the four ground electrodes. It does not jump to all four electrodes at the same time. This spreads the wear across four electrode surfaces instead of one as is the case with a standard single ground electrode spark plug.

Bosch says their tests have shown the new Platinum +4 plugs can improve fuel economy up to 4.8% over other competitive spark plugs. Fouling resistance is also said to be 33% better.

Though Bosch makes no specific mileage claims for their Platinum +4 spark plugs, they do say the plugs meet or exceed OEM requirements for 100,000 mile replacement intervals. Bosch says the plugs show almost no increase in firing voltage requirements after 100,000 miles of operation. Bosch has also run tests where the plugs have gone over 150,000 miles with no appreciable wear, so these would seem to be lifetime plugs for many vehicle applications (unless, of course, the engine is burning oil, in which case fouling might occur).

Another unique feature of the Platinum +4 is that the surface air gap between the center and four ground electrodes is factory present to 1.6 mm and is nonadjustable. No attempt should be made to adjust or change the air gap when the plugs are installed, even if the air gap specification is different from that specified for a standard spark plug. The wider gap of the Platinum +4 is necessary to achieve the advantages above.

Not For All Engines?

Bosch spark plugs are original equipment on most European makes, as well as some General Motors and Ford engines. Even so, Platinum +4 spark plugs may not be the best choice for replacing other brands of spark plugs on some applications. There are a lot of comments on various blogs by people who say they have experienced fouling and misfiring problems when they replaced their original equipment brand spark plugs with Bosch Platinum +4 spark plugs.

True or not, if the heat range of a replacement spark plug (any brand) is not the same or reasonably close to the original plug, it increases the risk of fouling and misfiring, especially if the vehicle is only used for short trip or stop-and-go driving. A spark plug that is too cold for an application can foul and misfire very quickly. This can happen with ANY brand of spark plugs, not just Bosch.

Bosch does test and compare the heat range of their spark plugs against the OEM spark plugs on engines where other brands of plugs are used. If Bosch has a spark plug that matches the heat range of the OEM plug, they will list their replacement plug for that application. If they do not have a spark plug that closely matches the OEM plug, they won't list it as an application.

Another consideration is the electrode configuration and how the ignition system operates. Bosch does not recommend using Platinum +4 spark plugs in engines that have a distributorless "waste spark" ignition system. On these applications, two spark plugs that are opposite each other in the firing order share an ignition coil. The problem is that when one spark plug fires on its compression stroke, the other fires on the exhaust stroke, but with reverse polarity. This can cause metal to transfer from the side ground electrodes to the center platinum electrode, creating conditions that may lead to misfires.

Bosch also does not recommend Platinum +4 spark plugs for certain turbocharged and supercharged engines, or for performance engines boosted with nitrous oxide.

More Bosch Spark Plugs

Since the introduction of the Platinum +4 spark plus, Bosch has also come out with slightly less expensive (around $4 to $5) Platinum +2 spark plugs which have two side electrodes instead of four. The performance advantages are similar, though the theoretically lifespan may be slightly less because the plug has two ground electrodes instead of four.

Their latest plug is the Bosch iR Fusion spark plug that feature an iridium/platinum center electrode with four yttrium side ground electrodes. This plug sells fro around $8 to $9 each. Like the Platinum +4, these plugs have a preset surface air gap of 1.6 mm. Bosch says the iR Fusion plugs can be used to replace OEM iridium spark plugs in many engines.

When choosing replacement spark plugs, follow the application listings in the catalog. If Bosch does not list one of their plugs for a specific engine application, there is probably a reason why (wrong heat range or incompatible with the type of ignition system or operating conditions). Use the type of plug Bosch recommends for your engine application (ir Fusion, Platinum +4, Platinum +2, Platinum Plus or Super Plus), or if there is no listing replace your old spark plugs with the same OEM brand.

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For technical information about Bosch platinum spark plugs, Click Here.

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