Lubrication 21 - Oil Cooling
No liquid medium used in the automobile reaches higher temperatures than the engine oil. The pictures show appropriate coolers from the past and the present. In the past it was considered especially sporty to place oil-air heat exchangers in front, under the bumper, as with the NSU TT (picture 1). Whereby, the long tube connections from the rear-mounted engine presented a relatively high risk, even if they were additionally armour-plated. Nowadays the oil cooling is integrated near the component to be cooled (picture 2). More often, however, the oil cooling is done by an oil coolant heat exchanger.
How it works
Circling heat affected parts, the oil absorbs heat from, e.g., the piston oil-spray cooling in the case of charged motors or the torque converter as in the automatic gearbox. Generally the circulation is taken care of by the oil pump, in rare cases the oil can be also thrown by spoon-shaped recesses in the gearwheels and thus be transported through pipelines and coolers. A thermostat switches the oil cooler on or off when the maximum or minimum temperature is reached, this is very important with e.g. air-cooled engines. Pump circulation maintenance is important, the pipelines should be checked at regular intervals. Leakage or abrasion of pipelines under pressure can have fatal results for the environment and/or for the aggregates to be cooled.
With lower performance engines the normal heat exchange through the oil sump is improved by:
- the choice of special materials (e.g. aluminium),
- the presence of cooling fins,
- a special oil guidance which prevents the hot oil from being redirected into the process immediately again.
Instead of an oil-air heat exchanger an oil-coolant heat exchanger can be integrated into the oil circulation. In this case, the faster heating coolant delivers warmth to the oil during the cold running phase. The reverse process is possible in the event of higher demands on the engine. 06/08