White deposits on spark plugs

There are many different symptoms by which you can determine the malfunction of the car engine or its systems, the color of soot on the spark plugs is one of them. If the spark plugs are covered with white soot — there is probably a problem with the power system, ignition, or the wrong fuel is used.

But there may be a more serious defect, such as the ingress of antifreeze in the combustion chamber. Our guide will help you to understand why there is white soot on your spark plugs, pinpoint the root cause and help you eliminate it.

Why white soot appears on the spark plugs

The reason for the formation of white soot on spark plugs is overheating as a result of ignition failure due to a sub-optimal gasoline/air ratio or a confused ignition.

Elevated temperatures affect in such a way that the dark carbon-containing deposits burn out and more persistent light ones remain.

It is possible to determine the exact problem that caused the white deposits by the structure of the deposits. Irregular, shiny, and massive, rough plaque have their own causes.

What causes faint white soot?

Faint white soot on spark plugs is a typical phenomenon when the engine runs on liquefied gas. A white residue on the spark plugs in the engine of a car without gas equipment indicates an unstable mixture or the presence of undesirable fuel additives. For example, leaded petrol which contains a lead additive, can leave silver-white deposits. Carburetor or injector sensor failures can also cause whitish deposits.

Causes of white deposits on spark plugs:

The cause of thin white sootWhat does it affect?What should be done?
Worn spark plugs or low-quality gasolineThe engine cycle is disturbed, the load on the cylinder block, slider-crank linkage, etc. is increased. Engine life is significantly reduced, lambda probe and catalyst failGlow and clean or replace the plugs
Low-octane fuelThe risk of mixture detonation increases, the wear of the engine is accelerated many times. Pistons, connecting rods, pins, valves and other parts suffer from shock loadsFill up with quality gasoline provided by the car manufacturer. Clean or change plugs
Unstable fuel-air mixtureThe engine cannot reach its normal operating rhythm, parts are subjected to load fluctuations and wear out fasterCheck operation of injector sensors (mass airflow sensor, air temperature sensor and an absolute pressure sensor), injectors, air tightness of intake

Why does white glossy soot appear on the spark plugs?

In itself, a thin white glossy soot on the spark plugs does not have a negative impact on the operation of the engine, but indicates the presence of several problems. For injector cars, the most common cause of white soot on spark plugs may be air leakage (checked by a smoke generator) or faulty injectors. If they are clogged or worn, they will dose fuel incorrectly.

If you see white soot on the spark plugs of an injected car, it is necessary to diagnose by OBD-2. If there is no leakage, it's necessary to check the mass airflow sensor, absolute pressure sensor and air temperature sensor. Excessively poor mixture is indicated by ECU errors P0171, P1124, P1135 and P1137.

If the car is old, with a carburetor, it could be:

  • dirt on the throttle;
  • wrong ignition advance angle;
  • clogged jets;
  • air leakage between carburetor and intake manifold.

Why is there a glossy white plaque on the spark plugs?

The cause of glossy white sootWhat does it affect?What should be done?
Fuel lean mixtureOverheating of cylinders and valves, increased wear of pistons, rings and cylinder walls, accelerated degradation of engine oil, reduced power and engine tractionCheck injector sensors, diagnose intake for air leaks
Inlet air intakeThe mixture becomes depleted, the consequences of which see in the previous pointCheck the intake system (pipes, receiver and intake manifold gaskets, injector seals) for leaks, e.g. with smoke, restore leaks
Injectors are cloggedThe engine actually receives less fuel, the engine power is reducedDiagnose the injectors of the injection system, clean and flush them, and if necessary — replace them with new ones
Untimely spark formation due to improperly set ignitionThe engine loses traction, overheats, accelerates its wear, increases the risk of burnt valves and other elements of the exhaust, the destruction of the catalystCheck gauge marks, timing belt installation, adjust ignition system
Wrong spark plug selectedDeterioration of spark formation, overheating of plugs and their accelerated wear, loss of tractionReplace the spark plugs, selecting a part with the caliper number prescribed by the manufacturer

White velvet soot on the spark plugs — what causes it?

Thick roughened soot on the white plugs indicates the ingress of foreign substances, such as antifreeze or oil, into the combustion chamber.

Detection of thick white deposits points to the necessity of urgent engine diagnostics. In such a way the timely replacement of valve seals or cylinder head gaskets will help to avoid expensive repair.

Thin white soot, which has a velvety texture, as in the case of glossy (slightly shiny) deposits, usually indicates improper mixture formation or untimely sparking. Its causes depend on the type of power system.

A very faint, velvety soot, like a light gloss, does not necessarily indicate a problem. It can also occur during normal operation of the engine (especially on gas), and the small thickness of the layer does not even let you unambiguously determine whether its texture is rough or shiny. So if the engine is running smoothly, there is no fuel overrun or antifreeze leakage, and there are no ECU errors, there is no cause for concern.

Causes of white velvet plaque on spark plugs

The cause of velvet white plaqueWhat does it affect?What should be done?
Incorrect spark plug operation, lack of energy for the sparkIncorrectly selected plug can not provide normal operation of the engine, so it runs unstable and wears out fasterReplace the spark plugs by matching the manufacturer's catalog
Problems with the ignition systemCheck coil(s), high-voltage wires, distributor (for cars with autotrembler), replace defective parts
Incorrect setting of the fuel injection systemInadequate fuel quantity-quality due to improper adjustment or clogged carburetorCheck carburetor adjustment, clean or replace it
On the injector ECU does not dose the mixture correctly due to incorrect sensor readings or injector malfunctionCarry out OBD-2 diagnostics, check correctness of mass airflow sensor or absolute pressure sensor and air temperature sensor readings, lambda probe, diagnose injectors. Replace defective parts
There is air leakage in the intake system, the mixture is depleted and the engine operates with overheating, the valves can burn out and the wear is acceleratedCheck the intake system for leaks using a smoke generator
Fuel filter is cloggedThe flow of gasoline is reduced, the mixture is depleted. Loss of traction, accelerated deterioration of engineReplace the fuel filter
Leaky cylinder-head gasket or duct integrity failureIf the cylinder-head gasket or ducts are damaged, coolant will enter the combustion chamber. In this case the oil can get into the antifreeze or vice versa. The engine cannot operate normally, emulsion is formed in the crankcase, lubrication deficiency and overheating occur, the internal combustion engine quickly failsCheck if there are no bubbles in the coolant expansion tank when the engine is running. Check if there are changes in the level of antifreeze. Check oil for light emulsion. If there are problems, remove the cylinder-head, inspect and, if necessary, repair the cylinder-head and replace the gasket.
Excessive amount of oil enters the combustion chamberCrankcase pressure, due to a drop in compression, drives oil into the intake. Deteriorates spark formation, accelerates engine wear, exhaust smokeCheck the oil catcher in the cylinder head, and if it is defective (e.g., falling off), repair it. If the cause is wear of rings and pistons — disassemble and defect the engine, carry out partial or complete overhaul
Piston rings do not cope with the drainage of excess lubricant from the walls of the cylinders, smoky exhaust, oil leakageDo anti-clogging of the engine, if it does not help — disassemble and defect the engine, repair the cylinder-head, change the rings (at least) and clean the pistons
Valve seals have lost elasticity. Oil leakage increases, there is smoke, the stability of operation is lost and the wear of the engine is accelerated.Replace the oil seals

How to clean spark plugs from white soot

If there are few deposits, cleaning the plugs from white fouling will allow them to continue to operate and avoid immediate replacement. There are two effective ways to remove plaque: mechanical and chemical, more about each of them below.

Before you remove white fouling from the plug, you need to eliminate the root cause of its appearance! After all, if we just remove white fouling from the electrode of the plug, the soot will return after 100-200 km of mileage, and the engine will continue to wear out at an accelerated rate.

The mechanical method of removing white deposits on the spark plugs

To remove fouling from the electrodes on the spark plug, you should choose the right abrasive. The best approach is a fine-grained (P240 and above) sandpaper.

Plaque in the gap between the electrodes can be carefully cleaned with a fine sandpaper, folding it in half. Be careful when doing this: if the spark plugs are properly cleaned, no scratches should be left!

It is not desirable to mechanically clean spark plugs with electrode plating or precious metal cladding (e.g. iridium). Rough machining can damage this layer and impair spark formation!

If white soot appears on new plugs, even though the car doesn't have gas equipment — before cleaning it, check if the spark plug matches the engine by its caliper number. If the part is selected incorrectly, there is no point in cleaning it — immediate replacement is required.

The chemical method of cleaning spark plugs from white plaque

The chemical method is more preferable, because it is possible to clean the plaque from the spark plug with chemicals without damaging its electrodes. This is especially important for expensive plugs with noble metals, whose thin layer is easily damaged by abrasives.

A variety of highly active agents can be used for it:

  • organic solvents (carbcleaner, gasoline, kerosene, acetone, paint thinners);
  • Rust Converter or a phosphoric acid solution;
  • vinegar or a 20% ammonium acetate solution;
  • Plumbing cleaners and plaque removers (like Cillit Bang).

Instructions on how to clean platinum and iridium spark plugs

  1. Treat the spark plug with solvent to degrease it.
  2. Place the working part in the cleaner.
  3. Keep it for 10 minutes to a few hours.
  4. Wash the spark plug again with solvent.

After removing the fouling, the plugs can be dried and installed in the engine. To speed up chemical reactions, it is possible to heat non-flammable liquids, but do not bring them to the boil!

Observe safety precautions when using chemicals for cleaning plugs. Use rubber gloves and a respirator to protect against corrosive fluids and fumes!

Remember, if new plugs are quickly covered with soot — you need to diagnose the power system, adjust the carburetor or change the injector sensors, check and clean the injectors. Have you found black and white soot on plugs or other unusual deposits — do not delay with diagnostics. It will avoid fatal consequences for your engine.

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