Spark Plugs – Frequently Asked Questions

Since 1959, DENSO has been the world leading pioneer of OE quality spark plugs, and they remain one of DENSO’s main specialisms today.

Through continual dedication to research and development, DENSO has produced some of the sector’s most important innovations, including U-groove technology, the world’s smallest iridium tip and the first protruding ground electrodes.

Now, DENSO manufactures OE-quality spark plugs to suit every application and motoring need across the following categories:

There are many factors to consider when choosing the right spark plug and during the installation process. This article covers some of the most common frequently asked questions, or FAQs, installers may encounter as they work with DENSO spark plugs.

20180315_F2_Spark Plug FAQs


How do I choose the right spark plug?

There are many factors to consider such as dimensions, projection and heat range. The easiest way to identify the right spark plug is via the DENSO e-catalogue, which can be found at /catalog/pv. Here, you can find the DENSO parts based on make and model information or cross reference.

Which spark plug should I use for LPG?

Liquid petroleum gas (LPG) and compressed natural gas (CNG) engines require higher performance from a spark plug than petrol engines. To identify the best spark plug for your car, use the DENSO e-catalogue at /catalog/pv.

Should I modify the electrode gap?

DENSO spark plugs are manufactured with a pre-set gap. With nickel plugs, especially with motorcycles, the gap may need adjustment. Always use a special spark plug gapping tool to change the gap. Do not change the gap on platinum, iridium or twin tip spark plugs, as the fine electrodes may get damaged.

How often should I replace my spark plugs?

Generally, the replacement interval is stated by the vehicle manufacturer. DENSO spark plugs follow the same interval. When upgrading the spark plugs, the interval may change. Driving on LPG or CNG will reduce the lifetime of a spark plug by 25-30%.

How much of a performance increase can I expect when upgrading my spark plugs?

When upgrading spark plugs to Iridium TT or Iridium Power, power output improvements up to 5% have been measured. However, this depends on the engine. Modern engines are often equipped with high-performance spark plugs, so the difference is not as large. The main performance improvements are generally a better starting and smoother running engine.

Should I apply grease to the spark plug thread?

If a thread lubricant such as grease is coated on the thread, tightening of the spark plug increases when applying the same torque; this can cause damage to the spark plug. Subsequently, vibrations may cause the plug to come loose. Because of this, DENSO recommends not using a thread lubricant.

Only in a few exceptional cases (such as with some LPG-powered forklifts) may a small amount of grease be required. In such cases, the spark plug will be supplied pre-lubricated.

What is the difference between side-electrodes and multi-ground electrodes?

With direct injected engines, the air-fuel mix near the spark plug can be locally very rich, which can cause carbon fouling on the ceramic insulator. Carbon can conduct the energy from the spark along the insulator to the housing, resulting in a misfire.

By adding side electrodes, the spark is guided away from the insulator onto the side electrode, preventing misfire. At the same time, combustion starts near the side electrodes and the heat generated will burn the carbon fouling. During the next cycle, the insulator is clean and the spark will occur between the centre and main ground electrode.

Further details of DENSO’s spark plug range are available online, on TecDoc or from your local DENSO Aftermarket sales contact.