TECH CASEBOOK: Idle gossip


Four generations of Cronjés had lived on the farm Kameeldoringfontein before somebody noticed that the youngest member of the family had a face that resembled that of a camel. Camel Cronjé had a long chin, fleshy lips and small ears and was only 12 when the community gave him his nickname, but he innocently believed the moniker was a reference to the name of the farm – not the animal.

Camel now owns the only local security company and his business operates a quartet of Nissan half-tonners.

Shortly after the warranties of the bakkies had lapsed, disaster struck. One started to smoke and use a lot of oil and soon afterwards it ran a big-end bearing.

We were asked to tow the bakkie and find out why this happened on such a low-mileage vehicle. I gave the job to August, who stripped the engine and found that the rings had carboned-up and were no longer functional. The oil looked very black and seemed to have been in the engine for longer than the usual 15 000 km.

Our first thought was that the bakkie wasn’t serviced regularly. I contacted Camel, told him what we found and asked him about the servicing arrangements. He said that all four bakkies received regular services at the Nissan dealership from which he bought them, but that he would task our garage with servicing them in future because they were out of warranty.

We briefly entertained the thought that this vehicle had skipped a service, but then Hennie made the bright suggestion that we should look at the state of the other bakkies. Their drivers brought them in and we took compression readings and sampled the oil. None were in as bad a state as the first one, but their compression readings were low, the oil looked unhealthy and their drivers admitted that they were sluggish and started to use oil. They were certainly affected by the same mechanical malady.

I held a meeting with the drivers and my mechanics. August thought that too many short trips were to blame, but I pointed out that while the frequent temperature change associated with this style of motoring is not ideal, many cars used for commuting suffer the same fate, and they don’t self-destruct in such a short time.

One of the drivers pointed out that the engines often do not get a chance to cool down in spite of the short distances they cover. On a cold night they’re kept running to keep the heater in operation, and on a hot day they’re not switched-off to keep the air conditioning blasting away.

The driver didn’t realise the importance of what he was saying, but my mechanics certainly did. Their eyes lit up and they all started to babble at once. They knew we had found the answer to Camel’s problems.

An engine is not designed to idle for hours on end. It can only do so if it gets a rich fuel/air mixture. The air speed in the manifold is too low for all the fuel droplets to march along like obedient soldiers. Against the manifold wall some of them actually creep back against the flow of the stream. A rich mixture at the entrance to the manifold will ensure that enough fuel reaches the combustion chamber to support combustion.

Such a condition causes some fuel to migrate past the rings into the sump and also promotes the formation of extra carbon that will cause the rings to stick. The oil degraded by petrol will soon lose its lubrication qualities and this will shorten the life of all engine components.

The engines of all four bakkies were overhauled; the drivers were advised to find alternative ways to stay comfortable.

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