A hot bearing is almost a sure sign of insufficient oil, and the trouble should be located and remedied immediately. Oil pumps stopping, clogged oil pipes or holes, frozen oil, or oil leaks are common causes of hot bearings. Never allow an engine to run with a hot bearing for any length of time, as the bearing or piston may seize tight and wreck the engine. Inspect the journals frequently to see if they are above normal temperature. A hot, binding bearing often causes the effect of an overload on the engine, slowing it down, and increasing the governor and fuel feed, this is followed in a short time by the bearing seizing. (123) Cold Weather Lubrication. It is by no means uncommon trouble in cold weather to find excessive fluctuations in pressure as the engine speed and temperature of the oil varies. Thus, if the pressure be set correctly with the engine running fast, and when just started up, it will be found, after half-an-hour’s running, that, with the engine turning slowly, the pressure is far too low, owing to the oil having become thin. If the pressure be then reset, it may be found on next starting up from cold that the gauge goes hard over, and may very easily be burst if the engine is run fast. The point is one to which many designers of engines pay far too little attention, though the difficulty may be very easily gotten over. The secret lies in having the by-pass outlet of most ample proportions, so that the excess of oil, however thick, can get away quite easily. If there is any throttling of the by-pass, back pressure must result with consequent increase of the pressure at which the by-pass valve comes into operation. In other words, the pressure of the main supply to the bearings will be increased. A writer to “The Motor,” London solved this problem in the following manner: