49.21. The level of coolant in the expansion tank is below normal, while its density is normal. This indicates:
UAРівень охолоджуючої рідини в розширювальному бачку нижче норми, а її щільність дорівнює нормі, що вказує:
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This exam question from the Traffic Rules of Ukraine concerns the safe operation of a vehicle and monitoring its technical condition before departure and while driving. A properly functioning cooling system directly affects engine reliability, the risk of overheating, and emergency stops on the road, which is why such checks are part of responsible driver behavior and are regularly encountered in the theoretical traffic rules exam.
The question tests the section of the Traffic Rules regarding technical condition and the prohibition of operation in the presence of malfunctions (in particular, the requirements of points 2.3 "a", 31.1, 31.4.7, and 31.5). The logic is simple: if the coolant level has dropped but its density remains normal, this means that the composition of the mixture has not changed significantly, and the fluid has simply been lost from the system. This sign is most typical for a loss of system tightness, both external (leakage through the radiator, hoses, clamps, reservoir, cap) and internal (entry into the cylinders or engine oil through the cylinder head gasket or other defects).
The option about boiling off looks plausible only in part: with intensive evaporation, water usually escapes faster, the concentration of antifreeze increases, and the density should change, so "normal density" does not fit well with this version. The answer mentioning only external leaks is too narrow, since the level can drop without visible puddles or wet traces. The practical conclusion for the driver in the context of the Traffic Rules of Ukraine: such a symptom should be regarded as a technical malfunction of the cooling system, measures should be taken to eliminate the cause, and the risk of overheating during further driving should not be ignored.
Clause 2.3 (subclause "a")
To ensure road safety, the driver is obliged: "before driving, to check and ensure the technical serviceability and completeness of the vehicle...".
This question is related to the driver's duty to monitor the technical condition: a decrease in the coolant level is a sign of a malfunction that must be detected before or during operation.
Clause 31.1
"The technical condition of vehicles and their equipment must comply with the requirements of standards relating to road safety and environmental protection, as well as the rules of technical operation, instructions of manufacturers, and other regulatory and technical documentation."
The logic of the question is as follows: if the fluid level drops, this indicates a deviation from the normal (serviceable) operation of the cooling system, i.e., a technical malfunction/non-compliance.
Clause 31.4.7
"Operation of vehicles is prohibited under the law in the presence of the following technical malfunctions and non-compliances: ... 31.4.7. loss of integrity (leakage) in the fuel, lubrication, or cooling systems."
This clause directly "highlights" the content of the correct answer: a drop in coolant level with normal density typically indicates fluid loss due to a breach of integrity (external or internal).
Clause 31.5
"If malfunctions specified in clause 31.4 of these Rules occur on the road, the driver must take measures to eliminate them, and if this is not possible, drive to a parking or repair location by the shortest route, observing safety measures."
This clause explains that a detected sign of loss of integrity (as a malfunction from the list in 31.4) requires the driver to act, not to ignore it.
Therefore, the correct answer is "External or internal loss of integrity (leakage).", given that by definition of the Traffic Rules, operation of a vehicle with a breached cooling system integrity (clause 31.4.7) is prohibited, and the driver is obliged to monitor technical serviceability and take action if a malfunction is detected (clauses 2.3 "a", 31.5).
In the engine cooling system, the level of coolant in the expansion tank must meet the standard. If the driver sees that the level is lower, this means that some of the fluid has disappeared from the system. It is also important to assess not only the quantity but also the condition of the fluid, particularly its density.
The density of the coolant actually shows whether its concentration has changed. When the fluid “evaporates” due to overheating or intense boiling, it is usually the water that is lost faster, and the mixture becomes more concentrated. In such a case, the density would change (usually increase). But in the question, it is stated that the density is normal, meaning the composition of the fluid has remained the same.
Therefore, the most logical explanation for a drop in level with normal density is that the fluid has not “changed composition” but has simply left the system. This is a sign of leakage. It can be external, when the coolant leaks outside through the radiator, hoses, loose clamps, a cracked tank, or a faulty cap that does not hold pressure. Such leaks are often noticeable during inspection by traces of leakage or damp spots.
Leakage can also be internal, when the fluid does not leak outside but gets into places where it should not be: for example, into the cylinders or engine oil due to a damaged cylinder head gasket or other defects. In this case, the level in the tank drops, but the density of the fluid in the tank may remain normal for some time, because the composition of the fluid does not “concentrate,” only its quantity decreases.
Therefore, the correct answer is "To external or internal leakage," since a drop in level with normal density means a loss of fluid without a change in its concentration, which is characteristic precisely of leakage outside or fluid entering inside the units due to leakage.