It will be found also that in most cases the hot-air stove of the carburetor may be dispensed with or adjusted. Usually provision is made on the hot-air stoves for allowing some cold air to enter, or to take cold air entirely. Where the carburetor is water-jacketed, there usually is a valve that may be closed to prevent the flow of hot water. Experiment will determine whether it is advisable to cut out the heat entirely on the individual carburetor, since all are not benefited by the change.
The water in the storage battery will evaporate more quickly in hot weather and where it has been necessary to replenish it once in two weeks in the winter, it will need to be done every week in hot weather. This is not entirely due to evaporation from heat but is accounted for in part by the fact that the engine starts easier and therefore less current is used for starting; also there is more daylight and the lamps are used less. Therefore the battery is more often in a fully charged condition, and in this condition the charging current causes more gas than when the battery is lower. This is due to the chemical action which decomposes the water, the hydrogen and oxygen gases passing off through the vent holes; the water escapes from this cause as gas and not as vapor, as it does when there is evaporation.
In hot weather city streets are generally sprinkled regularly and the country roads are oiled some time during the season. The novice going behind a street sprinkler, or reaching an oiled stretch of road, should exercise particular care to prevent skidding, as he would be unlikely to realize the danger unless he has experienced it once. This is explained fully in the part of this book devoted to skidding.
Hot weather softens grease, so that trouble may be experienced through grease or oil seeping out of transmission or differential cases, or from the grease cups. Many manufacturers recommend a heavier grease for summer than for winter to give the greatest efficiency. This softening of the grease is likely to make a little ring of grease around each cup, which will collect dust and give the car an unkempt appearance, besides there is the possibility of some of the dust working into the bearing. Grease cups must be kept turned down so that the dust is forced out, and then it should be carefully wiped off.
Every bearing needs additional care to keep dust out and lubricant in, but every moment spent in this way pays dividends in expense saved and comfort and freedom from annoyance on the road, so that the owner will do well to take note that hot weather calls for added care and precautions.
CHAPTER XXXI
HOT-WEATHER TIRE EXPANSION
There is considerable question whether the pressure on tires should be decreased during the hot summer days. Tire manufacturers claim, as a rule, that tires heat more on low pressure than when run at the full pressure given by them. They claim that even a slight decrease to offset any increase from heating, because of warmer temperature of the air, friction, and the hot pavements, will injure the tires. On the other hand, drivers of long experience insist that the car should be started out with the tires softer than in cold weather. Still others insist that the tire pressure demanded by the manufacturer makes the tire too hard for comfort and that when the pressure is increased by heat it makes the tire as hard as one of solid rubber. There is some truth on both sides.
There has been considerable criticism of the conclusions drawn from the writer’s experience with tires while on a summer tour, related in the previous chapter. He stated that there was a twelve-pound increase in a forty-mile run. This was disputed. Tests prove that he was right and that in city driving tires ordinarily heat up even when the conditions are not extreme.
To determine what effect the hot weather has on tires in the city, the author drove a 3200-pound Model L Locomobile, equipped all around with 34 × 41⁄2 inch tires, through the park and on Riverside Drive for fifteen miles at ordinary city-traffic speed, which always is under twenty miles an hour. The thermometer registered 86 degrees and the day was partly overcast, so that the full effect of the sun on the pavements was not obtained. The tires were inflated to full 90 pounds, which is the pressure recommended by many manufacturers.
At the end of the run, one tire registered 101 pounds, two were 100 pounds, and one was 99 pounds. The conditions were not excessive in any way and the weather was not abnormal, the road was smooth except for very short stretches, the speed was low, and the tires were of ample size for the weight of car and load.