CHAPTER VIII

SOMETIMES THE CAR SMOKES

The officer will get you if you don’t watch out, if you leave a trail of smoke behind you; then it will be:

“Good morning, Jedge, your Honor.”

“Guilty? Two dollars, please.”

“Cheap,” you say. Yes, if it were only the two dollars; but there is the time lost in appearing in court and then, really, you know, to make that smoke you were burning money.

Such smoke comes from two sources: Burning too much gasoline and using too much lubricating oil; usually the latter. Excessive use of gasoline comes from faulty carburetor adjustment, or poor design of carburetor or intake manifold, or keeping the engine cylinder at too low a temperature, because of the water being too cold in the cooling system.

In the latter case the carburetor may vaporize the gasoline properly, but it condenses in the cylinder and does not burn well and the part which is not consumed passes off as black smoke, which issues from the exhaust pipe.

We must have a certain amount of oxygen to consume the gasoline entirely. The size of the cylinder limits the amount of air (from which the oxygen is taken) which may be taken in and if the carburetor is adjusted to feed too much gasoline, there may not be enough oxygen present to consume it all. Practically speaking, what is not consumed forms carbon or smoke.

The obvious remedy is to adjust the carburetor so that no more gasoline will be fed to the engine than is required for running. In cold weather it is necessary, usually, to supply heat to the ingoing air at the mixing chamber of the carburetor, so that the vaporization will be complete.

A light blue smoke coming from the exhaust pipe indicates too much lubricating oil. This may be due to feeding too much oil or to running the engine a great deal with the throttle nearly closed. In order to draw a charge of gas into the cylinder the piston travels partly out of the cylinder and forms a vacuum. With the throttle wide open a high vacuum is not obtained because a large amount of gasoline and air is allowed to come in and fill the cylinder. When the engine is throttled down by closing the throttle, the air cannot enter in such a large quantity, and in consequence there is a decided vacuum in the cylinder on each intake stroke of the piston. This vacuum has a tendency to draw oil up past the piston into the combustion chamber, where it burns and forms smoke. This is why, when the machine is left at the curb with the engine running for any length of time, it will often be found to start away with clouds of smoke issuing from the exhaust.

In the same way, when the engine is running slowly, air passes through the carburetor so slowly that the gasoline is not broken up into very fine particles, consequently it does not fully vaporize and is very easily condensed. It forms liquid gasoline in the intake pipe or cylinder. This is called “loading up” and is responsible for black smoke when the machine is started.

One way of overcoming this is to supply a larger amount of heat than usual to the mixing chamber. Most carburetors are not designed to take care of this condition and the only remedy would be to stop the engine instead of allowing it to run while standing at the curb.

To overcome smoke from the oil which is drawn up past the piston, it is customary to have a groove turned in the piston under the lower piston ring, with five or six holes drilled in the groove through the piston. The piston ring then scrapes the oil from the cylinder wall into the groove and it is led back into the crank case through the piston walls. This prevents it from working up into the combustion chamber. Many manufacturers have this scheme on the very new models and repair men are using it on older models which were not turned out with it.

Sometimes the oil level will be found too high. This may be corrected often by lowering the oil troughs, or by filing off the dip on the bottom of the connecting rod so that it touches the oil with a narrowed surface.

In addition to the smoke resulting from too much gasoline or oil there is a large amount of carbon deposited in the cylinder which takes up space in the combustion chamber and raises the compression so high that pre-ignition occurs and the engine knocks. The car must then be taken to a repair shop to have the carbon burned or scraped out. This is expensive work and besides the car is laid up and one loses its use while the scraping is being done. The owner will see that he has been spending a lot of money to supply gasoline and oil that he didn’t need to use just to make smoke and carbon and expense and that he has lost from every point of view.

Smoke should not be confused with steam which issues from the exhaust pipe in cold weather. One of the products of combustion in the gas engine is water, a natural result of the breaking up of a hydro-carbon. This usually passes off at a high temperature as an invisible vapor. In cold weather it condenses immediately it strikes the air and is visible in the form that we call steam. Really it is a fog that we create. Therefore do not let the policeman summons you for having a smoking engine, when it is only steam issuing from the exhaust pipe. If he doesn’t know which it is you probably can convince him, by the color. If it is white it is steam, if it is black it is gasoline smoke, and if it is light blue it is the smoke from the lubricating oil. Therefore watch your exhaust for there are many eyes watching you just now in parks and city streets.