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Watch that gauge

20th August 1976, Page 58
20th August 1976
Page 58
Page 58, 20th August 1976 — Watch that gauge
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THE OIL FILM between the piston and cylinder bore is vital in transferring the heat to the coolant proper, while the lubricant splashing on the bores also helps to cool the engine components. On , the more highly rated diesels, a jet of lubricant is also played on the underside of the piston crown to provide extra cooling.

Any failure in the water cooling system will cause the lubrication system to be overloaded. Oil film on the bore can only withstand the high pressures applied by the piston so long as the temperature doesn't get too high. If it is too hot, the oil film breaks down, and piston scuffing or seizure is almost inevitable.

When the oil is too hot, its performance deteriorates to such an extent that vital components may fail. For example, the main and big end bearings rely on a flow of oil for cooling, and since there is a limit to the amount of heat that the bearing material will withstand, high temperatures are likely to lead to failure. Highly loaded surfaces such as the cams and followers, and the rockers will also be endangered.

Whenever the coolant temperature is high, the oil gets hot, simply because it is so near to the hottest parts of the engine. However, on engines with oil-to water coolers, the higher coolant temperature reduces the efficiency of the cooler, so the situation is made worse.

Overcooling of the oil can also bring problems, and this is why oil-to-air coolers are not used much on trucks nowadays. With vans used for a lot of stop-start driving, some condensation forms when the engine cools down and this contaminates the oil. Sludge is also likely to form if an engine is run too cold.

Whether an engine is fitted with an oil cooler or not, it is important to keep the sump topped up to the level recommended by the manufacturer -remember, this isn't an oil reserve, but all the oil is in use all the time,

Since most of the heat transferred through the walls o the sump to the air, avoic shrouding the sump in any way The driver must make sun that he doesn't overload tho lubricant by allowing the engini to overheat, especially sinci efficient cooling starts with ; regular check on the coolan level. A good driver keeps hi' eye on the temperature gauge.

A lot of discipline is needec to stop when the engine doe: overheat, especially when thi schedule is tight; in the lonj run, though, stopping will savâ–  much more money than gettinf to the depot on time with ruined engine.

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