Top-end cleaning

Contamination costs money. Focusing on the ‘dry’ side of the engine, Rob Marshall looks at the problems it causes and the options available to effect a cure.

Focusing on the ‘dry’ side of the engine, we look at curing potential contamination.

Coping with the residues that remain after burning petrol and diesel in car engines has always been a challenge. As vehicles age, these deposits can accumulate and, at best, raise fuel consumption and exhaust emissions. Due to the process being gradual and invisible, the driver tends not to notice until the car fails an MOT, an engine management lamp illuminates, or a breakdown occurs.

Detergents in modern engine oils assist in dislodging and holding this harmful contamination in suspension, until the next oil change drains them out. Should the recommended service intervals be excessive, or skipped –or if the car experiences regular short trips – the oil can become over-saturated with deposits, causing them to fall out of the lubricant, to form a tar-like sludge.

As this is such a hot topic, CM’S February 2020 issue focused on how to keep the lubrication system in good health, while our April 2020 edition on turbochargers explained how a weakened lubrication system can cause severe and expensive mechanical failure.

While the in-depth article on these pages references the lubrication system, it focuses more on keeping the intake manifold, cylinder-head inlet ports, exhaust gas recirculation (EGR) system and turbocharger clean.

The dirty secret

Apart from residual moisture within the filtered air that is drawn into the engine, it may be thought that the intake manifold especially would remain perfectly clean until the car is scrapped. In practice, intake contamination is a growing problem. A root cause is the crankcase breather. In our imperfect world, ‘blow by’ gases leak past the engine’s piston rings and certain constituents of the engine oil vapourise as the lubricant ages. These oily fumes have to go somewhere and, because environmental legislation dictates that they must not vent into the atmosphere, the only option is to direct them into the engine for burning.

Most engines employ ‘positive crankcase ventilation’ (PCV), where the engine crankcase is connected to the intake manifold via a pipe and, in most cases, a PCV valve. The gases, however, introduce oil vapour to the inlet. When a thin film becomes deposited within the tract, the oil’s sticky viscosity improvers attract contaminations from the airstream, causing them to build.

For engines that direct an excessive quantity of oil into the inlet (either through poor design, or excessive wear), the aftermarket parts industry has developed catch-cans that separate some of the oil from these blow-by gases. These are not always totally effective at preventing viscosity improvers from coating the inside surfaces of the air intake and consider that modifying the crankcase ventilation system to exhale into the surrounding air is not only illegal but could also be dangerous.

Yet, to reduce temperatures within the combustion chambers and lower NOX pollution, exhaust gas recirculation (EGR) valves introduce a further complication. As their name implies, they regulate dirty exhaust gases into the inlet, the soot content from which binds to the viscosity improvers within the intake. As the contamination builds, the intake becomes restricted, the engine can draw in less air, and

effectively suffocates. Should swirl-flaps be fitted within the inlet manifold, their movement can be restricted, which can cause mechanical damage. As modern diesel engines possess throttle bodies

(to assist with EGR operation and DPF regeneration), sensors, motors and flaps can also become coated with the sludgy deposits, which affect their operation. Sludged-up engine inlet valves can also have their movements restricted.

Directly affected: modern engines

Even though older petrol engines possessed PCV systems (with many of them lacking a separate valve), their intakes remained relatively clean. As air entered the carburettor almost immediately after passing through the air filter, the air and fuel mixture would enter the air intake together. Petrol is an effective solvent, so any lingering oil from the crankcase ventilation system would be washed into the engine cylinder and burnt.

Fuel injection presents a slightly different challenge. Early multipoint versions relied on ‘indirect’, or ‘port’ injection, where the injector was positioned behind the inlet valve, allowing some fuel to be washed over the valve and intake, cleansing them of most deposits. In a bid to reduce CO2 output and boost engine efficiency, the fuel injector was repositioned directly into the combustion chamber: direct injection was born. While direct-injection (DI) diesel engines have been around for some time in motor car applications, gasoline direct injection (GDI) for petrols became popular from the mid-2000s.

Unfortunately, relocating the fuel injector removed the cleaning effect within the intake. GDI and DI engines, therefore, are more prone to dirty and partially blocked intakes, compared to their port-injected predecessors. The higher temperatures experienced by

GDI engines bakes the contamination into a rubbery-type deposit, contrasted with the oily sludge found more commonly on diesels.

INTAKE VALVE FUEL INJECTOR Traditionally on petrol engines, the fuel injector (labelled) has been positioned behind the intake valve (labelled), the fuel from which offers a cleaning benefit before being burnt.

Traditionally, additives that discouraged deposits within the fuel system were dosed into the fuel tank as a periodic preventative measure. Removing carbon from the engine dictated treating it more directly, by pouring it into the intake of a running engine. Many modern treatments work in the same way – but read the instructions thoroughly. Diesels especially are vulnerable to severe engine damage from ‘hydrolocking’, caused by ingesting excessive quantities of liquid.

You can clean such sensors manually but they tend to be very delicate. Generally, aerosol cans of carburettor, or brake cleaner, can be used. Some companies sell a dedicated intake cleaner solution, which tends not to leave any residue behind.

A valuable way to discover the extent of contamination is to remove and inspect a sensor, should one be mounted to either the throttle body, or intake. The clogged state of this air temperature sensor means that the engine will not be receiving accurate data and that intake cleaning is necessary.