What do technicians need to know about spark plugs? DENSO answers the key questions

As an original equipment manufacturer and supplier, DENSO not only provides its customers with the quality products for which it’s so renowned, it also gives them the technical support they need to get the best from them. As a result, the DENSO Aftermarket technical team is always ready and willing to help aftermarket professionals with the answers to their questions, particularly on the topic of spark plugs, such as these presented to Praveen Kumar Saragadam, Application & Development Engineer, DENSO Europe

Which is the right spark plug?

Praveen Saragadam (PS): “There are many key factors to consider, such as dimensions, projection, hex and thread diameter, length and specifications such as nickel, iridium or platinum, as well as the heat range. The easiest way to identify the correct spark plug is by checking out the DENSO E-Catalogue. This resource allows users to locate the appropriate DENSO parts, based on make and model information or by cross-referencing.”

Which spark plug should be used for liquid petroleum gas (LPG) applications?

PS: “LPG and compressed natural gas (CNG) engines require a higher performance a spark plug than petrol engines. The combustion temperatures for LPG/CNG also fluctuate more than a petrol engine, thus contributing to reduced service life of up to 30%. Therefore our recommendation is to upgrade to longer DENSO Iridium spark plugs, which improve ignition and engine performance, as well as extend the spark plug replacement interval. The DENSO Twin Tip (TT) range, offers an ideal upgrade to meet these LPG/CNG requirements, but more information on how spark plugs perform with LPG/CNG can be found in DENSO Spark plug manual page: 61.”

Should the electrode gap be modified?

PS: “DENSO’s spark plugs are manufactured with a pre-set gap. However, with nickel plugs, especially for motorcycles, the gap may need adjusting. In that case, technicians should always use a special spark plug gapping tool to alter the opening. Technicians should never change the gap on platinum, iridium or TT spark plugs, though, as doing so beyond the material limitations will damage the fine electrodes, which invalidates the warranty.”

How often should spark plugs be replaced?

PS: “Generally, the replacement interval is confirmed by the vehicle manufacturer (VM) – DENSO’s spark plugs mirror that advice. When upgrading spark plugs, though, the interval may alter and driving on LPG or CNG will shorten the life of the plug. It is recommended that spark plugs are checked regularly and should be replaced when they’re ‘fouled’, which is when a plug has become covered in a substance, like oil, fuel or carbon, or it has become blistered from running at too hot a temperature.”

Should grease be applied to the spark plug thread?

PS: “DENSO recommends not using a thread lubricants, which can cause damage to the spark plug and consequently, vibrations may cause the plug to become loose.

“Only in a few exceptional cases, such as LPG-powered forklifts, should a small amount of grease be needed, and in that case, the spark plug will be pre-lubricated.”

Can a multi-ground spark plug be replaced by a single-ground spark plug?

PS: “A multi-ground electrode is preferred by some engine manufacturers and VMs because of the extended lifetime of the additional ground electrodes. Extending a spark plug’s service interval, without the use of precious metals, is a very cost-effective solution.

“Multi-ground spark plugs are designed specifically for long life rather than performance, but replacing a multi-ground spark plug with a single ground spark plug will improve performance, at the sacrifice of reduced service life.

“Upgrading a multi-ground electrode spark plug to a long-life iridium spark plug, like the DENSO Iridium TT, however, will combine both performance and durability.”

Are counterfeit spark plugs a problem?

PS: “In short, yes. As internet shopping and e-commerce have become so prominent, motorists and technicians alike now have access to a global marketplace for vehicle components and unfortunately, counterfeit items are often among them.

Please be aware the counterfeit products are manufactured with cheap quality materials and can lead to serious engine damages. Therefore, DENSO will not take responsibility for claims caused by counterfeit products.”

How to avoid counterfeit plugs?

PS: “First, only ever purchase from an authorised distributor. While e-commerce websites may appear to have great deals and low prices, often a deal that looks too be good to be true, is. To demonstrate the differences between authentic products and counterfeits, DENSO has created several comparisons to help technicians identify a genuine DENSO spark plug.

“One of the biggest signs of a counterfeit is the difference in how the product may look. Simple things, such as the branding containing spelling mistakes, is an indication of a non-genuine part. A genuine DENSO spark plug should have a uniform insulator shape, be white in colour, and the width of the ground electrode should be consistent.

“The packaging may also contain some obvious signs that the spark plug is not genuine. DENSO spark plugs are only manufactured in Japan, Indonesia, China or the United States of America. So, if it’s branded a DENSO component, but has been manufactured outside of these areas, then it is not genuine.

“Another item to check is the barcode and production code. DENSO products have complete traceability throughout the supply chain, and non-matching production codes in a sealed pack or four or 10 plugs are likely to indicate they are counterfeits. Technicians should also always check the barcode and production code numbers and if in doubt, they should call their local DENSO representative who can advise them.

“Finally, all DENSO spark plugs go through a stringent manufacturing process, so to check against the official specifications in the DENSO catalogue is a simple and effective method of identifying a counterfeit.”

The following checks are recommended:

  • A feeler gauge or coin-style gapping tool can measure the electrode gap distance. The correct distance will be stated in DENSO specifications.
  • A caliper tool can measure the diameter of the ceramic part. If this is not in line with official DENSO specifications, the part is non-genuine.
  • The ground electrode angle can also be assessed. If this deviates from the correct angle, spark functionality will be negatively impacted.
  • Measuring the gap between the gasket and the spark plug body and checking the length of the spark plug thread and overall plug will also identify a counterfeit, if not in line with DENSO specifications.

Find out more about DENSO Spark Plugs