Prolonged use of a car engine in conditions where the oil cannot reach its correct working temperature will cause sludge formation and crankcase oil dilution, leading to excessive wear especially in the cylinder bores. Optimum engine power will only be delivered at correct temperatures. The elimination of drag in engines caused by cold oil is a most important consideration, especially with a racing engine, revving the engine without a load will not put much heat into the oil and devices for preheating the oil may not be available.
It is therefore desirable to control of the oil flow through the cooler by a thermostatic device, we call an oilstat, set to divert oil to the cooler at 80°C (although a wide range of settings is available for special applications). This is the minimum temperature required to evaporate and dispel contaminating substances.
The bodies of the these units are die cast aluminium. Control is by a "waxstat", a mass produced item built to highest standards. They are light enough to be supported by the hoses, however a bracket is supplied with the slightly heavier OT/2, if further restraint is required. The oilstats should only be used where oil cooling is adequate, the sensing device will suffer permanent damage above 140°C, replacements are available.