Winter servicing advice from NGK

December 21, 2017
Winter servicing advice from NGK
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Ignition specialist NGK has issued some timely advice on winter servicing.


The company says that low ambient temperatures can place extra stress on all engine and ancillary components, especially at start up. Extra demand is placed on the electrical components, the starter motor possibly robbing some electrical energy usually available for the ignition system in SI engines and the preheating system in CI engines. As such, spark and glow plug replacement should be part of the winter service as they play an integral role in a vehicle’s economy and emissions’ performance.

Tim Howes, Deputy General Manager also points out that modern pump fuels have higher aromatic contents in order to raise the octane rating sufficiently. This means that there is more potential for carbon to be deposited on the insulator nose of a spark plug. Cars used under frequent stop start conditions will be more prone to this carbon fouling; the plugs may not reach a sufficient temperature for a long enough period of time to burn off the carbon deposits. 

The accumulation of dry carbon does not usually reduce the insulation resistance to the point at which misfiring will occur, the problem occurs when the carbon is wetted by poorly vapourised fuel. The fuel soaked carbon rapidly reduces the insulation properties and left unchecked can allow some voltage to leak away to ground reducing the spark energy. In short this could mean the car will be difficult to start or not start at all.

NGK stress that many spark plug types are specifically engineered for the intended application. This includes certain anti-cold fouling capabilities and the correct choice of heat range. If therefore the incorrect spark plug type is installed the possibility of poor starting performance is substantially increased.  Tim also says that it is worth removing the plugs to actually check them and this is much easier to do in a workshop that at the side of a road in a breakdown.

Methods of combating potential fouling include the use of semi surface discharge plugs, intermittent discharge plugs and supplementary gap plugs. These intelligent designs force the spark to discharge across to the ground electrodes or a chosen part of the metal shell. In order to avoid complaints about poor starting and misfiring under load it is more important than ever to select the correct spark plug type for the engine.

With regard to diesels, low battery voltage can affect the ability of cut off solenoids to operate correctly even if they have enough energy to crank the engine. Similarly, a low battery voltage can mean that the voltage available to operate the glow plugs is not sufficient to allow the probes to get to their optimum temperature. The pre-heat time is so short now that a good electrical supply and ground is essential.

Many modern high-speed diesel engines rely on high performance glow plugs not only to aid starting, but also to improve the general drivability during the first few minutes after starting up.  The glow plugs often go through three stages of heating, pre-heating (prior to cranking), start heating (during cranking) and post-heating (after the engine has fired). The post heating types are common now and often are engineered with their own self-regulating devices inside.

Some engine manufacturers favour the use of ceramic glow plugs. These have extremely fast heating times, typically two seconds to reach 1000°C with final temperatures exceeding 1350°C.  They also have very good durability qualities and can operate for up to twice as many times as conventional metal types.

Cars that have little or no difficulty starting in mild weather can suddenly become reluctant to fire up when the ambient temperature drops significantly. Through the summer months it is quite possible that the car has been starting up on, for example three out of four glow plugs. In cold conditions the deficiency in the fourth combustion chamber becomes too great.

Tim says the best approach is not to make assumptions but, as with all diagnostic work, adopt a logical procedure for checking the system with a thorough voltage check.  A resistance check will also identify either a broken heating or regulating coil or poor ground connection. 

When it comes to glow plug choice many technicians will ensure that the voltage is compatible but something that is not always considered is the current draw. Depending on the design, current draw characteristics can vary from an initial inrush value in excess of 80 amps to a stable current around 6 amps.  NGK produces glow plugs with lower current draw whilst maintaining the required heating characteristics.

Manufacturers usually mark glow plugs with a voltage, but care must be taken as this is often a ‘rated voltage’ or test voltage for taking current and temperature data. It could be found that a glow plug marked 10.5 V is actually designed to operate at 6.0 V for most of its cycle when in the vehicle. 

Again regarding the supply voltage, under cranking the glow plug may be supplied at 9.0 V and once the engine has started the charging system will bring the battery voltage (and the glow plug supply) up to over 14.0 V. A typical stable current at the rated voltage might be 6.0 A, but many modern vehicle systems operate so quickly that ‘in the vehicle’ testing could prove impossible as the voltage is cut before this stable condition is reached.

Once removed the glow plug can provide the vital information regarding engine condition.  Damaged heater probes can be attributed to several different faulty components. Poor spray patterns from injectors can cause local hot spots that partially melt the heater tube.  Worn guides, rings or turbo charger can lead to excessive oil reaching the combustion chamber; this can have a similar effect on the heater probe due to overheating caused by abnormal combustion. 

A bulging or swollen heater tube can be an indication that excessive voltage has been applied.  Stop to think about the excessive voltage!  Is it the correct glow plug? Is the controller applying the voltage on too long? Don’t overlook something as simple as to make sure that the alternator is not overcharging!

Another simple check is to ensure that the terminal nut has not been over-tightened. Sometimes this can cause the lead, busbar or even the insulated centre electrode to be grounded, resulting in a direct short and no heating effect. 

When installing the new plugs technicians should ensure that the threads in the cylinder head are clean and in good condition do not be tempted to apply any anti seize compounds. This can easily result in over torque and distortion of the metal shell. Breakage is then more likely especially upon subsequent removal. 

The glow plug also relies on a good contact with the material of the cylinder head to dissipate some of the heat generated. Greases can restrict this heat flow and again shorten the life of the plug.
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