1. The driver can generally detect a slight smoke rising from the engine, and a smell of burnt paint and burnt oil.
2. A peculiar tapping sound becomes audible.
3. The engine will continue firing for a few revolutions after the current has been switched off or the burners extinguished.
4. Steam issues from the cooling water or the water blows out of the overflow pipe.
What to do when the Motor Heats.—As soon as any of the above symptoms are noticed—
(1) The motor should be stopped at once.
(2) Paraffin should be copiously injected into the cylinders and the engine turned by hand to free the piston-rings.
(3) The parts should then be allowed to cool.
(4) Change the exhaust springs.
N.B. Do not pour cold water into the cylinder jackets, for fear of cracking them, but rather pour into the tank so as to warm the water before it reaches the cylinders.
Dangers of a 'Seize.'—Overheating of the engine to this extent should be guarded against, for it is liable to cause scoring of the cylinder walls, and may warp the cylinder-head joint (if there is one), which will necessitate re-making the faces a tedious and difficult task. The exhaust-valve lifters may become bound, the excess of heat will also cause the valve-springs, piston-rings (and possibly the occupants of the car), to lose their temper; apart from the above no damaging effects are usual.
Precautions.—To enable the driver to verify the water circulation a 'manometer ' should be placed on the dashboard to indicate the pressure of water, or a tap or float arrangement may be connected with the piping, so as to show whether the circulation is all right. During hard frost this is especially important, for should the circulation cease, the radiator, a pipe or even the water-jacket itself, may be easily burst by the frost.
B. Starvation of Carburator.—A motor may stop from other causes besides overheating—for instance, no petrol may
