lubrication of the engine and it must be remembered also that in cold weather when the oil is thick a different adjustment will be necessary from that found suitable in warm weather. It is most important that the lubrication should be regular, and with good oil but not too much; for too much oil will spoil the sparking plugs, clog the valves, and interfere with the explosive mixture. For this reason the lubricators should always be carefully closed when stopping. If a Dubrulle mechanical lubricator is used, examine the ball valves sometimes, and do not trust entirely to the sight feed. If a pressure type lubricator is used, see that the stopper is tight, for if the pressure from the exhaust leaks the lubrication will stop and in some cars the supply of petrol too.
It sometimes happens that an oil pipe or hole is stopped up and wants cleaning, or perhaps the plug at the bottom of the crank chamber has come unscrewed with the vibration and dropped off, losing all the oil, in which the cranks should always dip. The proper amount of oil for each crank case is generally at least half a pint; an extra lubricator to the cylinders or base chamber should always be fitted, so that a little extra oil can be fed in by hand, if there is any doubt about the engine getting enough.
The following are additional causes of overheating. They are, however, of very rare occurrence:—
Cause 4.—The head joint may leak and admit water into the cylinders.
Cause 5.—In some engines if the throttle is kept full open, so as to admit too powerful a charge of gas, overheating will result.
Cause 6.—Finally, a thick incrustation on the walls of the water jacket, due to the use of bad water, will prevent the cooling water from taking up the excess of heat from the cylinder.
Remarks on Overheating.—How to tell when a Motor is Overheating.—The symptoms are:—
