CHAPTER XI

THINGS WHICH MAKE GAS BILLS HIGH

There are other things which affect the amount of gas consumed which need the attention of the automobile owner. One of the common things, mentioned in the preceding chapter, concerns the intake manifold, which has to do with the distribution of the gas mixture from the carburetor to the several cylinders. A leak at the carburetor side would prevent drawing into the manifold a sufficient supply of the mixture, so that the cylinders would be scantily supplied—perhaps one or more not supplied at all. Likewise air would be drawn into the manifold through the leak, and this would thin the mixture coming from the carburetor. As the mixture in the cylinders would be thin it would not compress properly, the firing pressure would be poor, the mixture would fire badly or not at all, and the power would be lessened.

The natural thing to do when the misfiring is noticed is to open the spray or needle valve, admitting more gasoline to the mixing chamber and making a higher consumption with no gain in power. The proper thing to do, however, is to look for a leak in the manifold.

If the leak is on the cylinder side of the manifold, it might be at one or all of the cylinders. The result would be the same as in the case just cited, a poor supply of the mixture, or some of the cylinders might be properly supplied and work all right, while others might be short of the mixture and might not fire at all. The loss might be sufficient to affect seriously the power and lessen the speed of the car.

The manifold ought not to become loosened in the ordinary use of the car. There have been cases where vibration has done it, but the usual trouble is where the manifold has been removed for some purpose and improperly replaced. Copper and asbestos gaskets ordinarily are used, and these may be dented or jammed out of shape so that the joint is not tight, or there might have been no shellac handy, or the bolts may not have been tightened enough. Whatever the reason, the leak makes a weak mixture, and the first thought of the chauffeur or the average garage man is to increase the gasoline at the spray nozzle of the carburetor to make the mixture of the right proportion to fire. On account of the mixture being made in the intake manifold, instead of the carburetor, as it should be, the work is not efficiently done and gasoline is wasted, the result being the increase of the expense account.

One of the most common causes of gas loss is from leaky supply pipes. Where there is a solid pipe from tank to carburetor the only leak, barring a break or perforation of the pipe, would be at the connection with the tank or the carburetor. Vibration might cause the joints to loosen, though if they are put together properly with shellac, soap or some equivalent, and are thoroughly tightened, there ought not to be any loosening. It is needless, but how often we see a car dripping gasoline at considerable loss. It is also dangerous, for a stray flame or spark may ignite the gas.

There is another leak of the same nature which is quite as expensive, and that is of lubricating oil. If you do not believe it to be prevalent or serious in extent, you have only to watch places where automobiles stand frequently along the curb and notice the pools of oil on the pavement. These come from leaky crank cases, transmission gear cases, rear-axle gear (differential) cases, or from a faulty distributor. In most cases it is only a matter of tightening a few bolts or connections occasionally; but with oil at present prices it is a serious matter.

Another leak which needs to be corrected frequently is at the valves. So much has been written about the care of valves that it would seem superfluous to refer to it, but regrinding and proper care pay big dividends in efficiency and should be on the regular program. There is a leak at the valve, however, seldom mentioned, though quite as serious as the others, which is due to worn valve stems.

The valve stems should fit snugly in the guides; if they do not, air will be drawn past the stem into the cylinder on the suction stroke and thin down the mixture so that the engine runs irregularly, unless more gasoline is supplied at the spray nozzle, and throttling down to a reasonable idling speed is impossible. If the exhaust valve guide is worn there will be a hissing sound that is objectionable.

The purpose of repeating this caution as to mixture thinning is to make it plain that wherever there is a leak between the carburetor and the cylinder it lets in air and thins the mixture so that it is necessary to feed in more gasoline to get a mixture that will fire and that is wasteful, for a mixture made anywhere else than in the carburetor is less efficiently accomplished.

The burned gases pass out through the exhaust valve side and in so doing often deposit small pieces of carbon, which keep the valve from seating properly and let perfectly good mixture escape. If not cleaned often, the heat and constant tapping of the valve against the seat will hammer the carbon fast to the valve or seat as though it had been fused there. Carbon must be scraped off frequently and as often as necessary the valve should be reground into the seat.

Piston rings which are not pinned often work around until the slots are in line and the mixture will blow through. If the rings will not stay in place a pin should be put in the ring groove on the piston to prevent the ring from working around and the slots should be staggered, so that no two are in line. Naturally the rings must be kept free from carbon or gum from the oil or they will freeze to the groove and leak mixture.

In older cars the cylinder may be worn oval, so that the piston and its rings do not fit. When the cylinder is oval the piston will not pump in the mixture properly, and when the explosion occurs much of the burned gas will be forced down into the crank case. One of the products of combustion is water, which is exhausted in the form of vapor. When it gets into the crank case and condenses, forming water, it collects under the oil. In cleaning out and replacing the oil, if water is found, it always indicates a tendency to oval in the cylinder. This is caused by the thrust of the connecting rod being against one side on the up stroke and against the other on the down stroke.

With everything else there may be a loss of gasoline by reason of poor adjustment of the carburetor. The adjustment should be such as to make the mixture as lean as possible and have it fire readily, and to have the float not too high. One sure indication that the mixture is too rich is when black smoke is given off. Black smoke always indicates excess gasoline—burning money. As has been told in another chapter, there is another kind of smoke to guard against, but if the owner will make sure that he is not exhausting black smoke he need not worry about the price of gasoline, and a little judgment and care will eliminate many of the items of upkeep expense.