TORQUE SHOP #9
Our mechanical engineer interprets (or debunks) what these motorists were told by their mechanics.
A mechanic told me that my car had a “head gasket leak”. He showed me some evidence of oil seepage and recommended that I have it fixed. He said that it would get worse, even if a repair was not urgent. Exactly how serious is this? The head gasket is the seal between an engine’s cylinder block and cylinder head.
The piston moves in the cylinder block and the head is where the valves are located and where combustion is initiated. As such, the head experiences very high pressures and is subjected to much of the heat generated during combustion. The head gasket also isolates the oil and coolant channels between the block and the cylinder head. So the importance of the head gasket is quite obvious.
A small leak at the gasket – the joint between the head and the block – is not serious enough to cause complications. However, no gasket leak will ever “self-heal”. It will only get worse over time. If allowed to persist, the gasket will likely rupture, causing oil contamination of the coolant and vice-versa.
This is a condition that must be avoided to prevent the inevitable damage caused by coolant mixing with engine oil. This results in the deterioration of engine lubrication and, ultimately, failure of various moving components, which will mean a full engine overhaul and a hefty repair bill.
For a fraction of the cost, a gasket replacement is a worthwhile exercise. During my car’s last routine servicing, my mechanic recommended that I do an engine flush to clear carbon build-up. Is this useful or just a way for the workshop to earn more money? What can I do to prevent carbon build-up in the first place? In an engine flush, a liquid is poured into the oil-filler on the valve cover to mix with the engine oil. The engine is then run for a few minutes and the mixture is drained – along with sludge and contaminants. The engine is then replenished with fresh oil. Between gaps in the moving parts of an engine, there is a
AN ENGINE THAT IS REGULARLY SERVICED, FILLED WITH GOOD-QUALITY LUBRICANT AND FITTED WITH A RECOMMENDED OIL FILTER WILL NOT REQUIRE FLUSHING.
thin film of oil that is critical to preventing wear. An engine flush could strip off this thin film. An engine that is regularly serviced, filled with goodquality lubricant and fitted with a recommended oil filter will not require flushing – even after 300,000 kilometres. If there is a major engine problem, such as worn mainbearings or leaking piston rings, then these parts should be replaced. During replacement, the engine will be cleaned. And during re-assembly, parts are always coated with oil to initiate the thin film of lubricant mentioned earlier. Even in extreme situations where there is contaminant build-up in the engine (such as radiator coolant getting into the engine), it is better to perform a short-interval oil change (perhaps within the first 1000 kilometres) after the repair work is completed to flush out remnants of water. There is no need for an engine flush. In any case, engine oils contain a number of additives, including detergents. Recently, my car lost power while accelerating. It also emitted white and blue smoke. My mechanic told me that I had to replace the “PCV valve”. What does this part do and is the problem serious? A small amount of combusted gases will inevitably escape past the piston rings into the crankcase where the engine’s oil is “stored”.
If allowed to build up, the gases will create a high pressure in the crankcase and cause deterioration of the content of the oil sump in the crankcase. Eventually, sludge will form and the engine oil will lose its lubricating properties.
In the early days, the blowby gases were vented out of the crankcase and into the atmosphere. Eliminating this air pollutant was one of the first emissions-control processes. These gases are now channelled back into the combustion chamber via the intake manifold, while the crankcase is provided with freshair ventilation via the air-filter.
All cars have what is called the positive crankcase ventilation (PCV) valve. This simple but effective component lies in the plumbing between the crankcase and intake manifold, and facilitates the recycling of the blow-by.
It is designed to open at a specific pressure differential between the intake manifold and crankcase. This is so that sufficient ventilation is provided while preventing a condition of vacuum in the crankcase that would cause excessive oil to be drawn by the intake manifold.
A PCV valve that is stuck “open” will lead to oil build-up in the intake manifold, leading to a plume of bluish white smoke when accelerating. On the other hand, a PCV valve that is jammed “shut” will cause pressure build-up to a point where air-oil fumes from the crankcase will be diverted to the air filter. This also results in bluish white smoke when accelerating.
The condition is not serious, nor is it expensive to fix. But it should be fixed. Prolonged running of the car with a faulty PCV valve will lead to formation of sludge in the engine oil or contamination of the air filter, intake manifold as well as other air and vacuum lines.
Questionable recommendations by mechanics could throw a spanner in the repair works.