If the liquid boils, the heat removal from the walls to the vapor bubbles will become negligible …
Here I will make a reservation right away: there are things that every motorist should have at least a minimal idea of, whether he is sitting at the wheel of a decrepit Moskvich or a sparkling Lexus. Our roads are so insidious that any car can instantly be left without oil in the engine or, for example, coolant … Then, whether we like it or not, the trip will have to be interrupted.
But the trouble, for a superficial look, is not obvious: a trickle of hot “Tosol” runs from under the cork of the expansion tank. What to do - maybe drain the surplus? (There were such heroes!) Here it is worth recalling the basics: if the cooling system is leaking, it does not support the excess pressure provided by the designer. It is necessary to raise the boiling point of the coolant (Fig. 1). The won 15–20 degrees will not allow you to “boil” the motor even with a high load in hot weather. So, what does the Tosola trick say? The system communicates with the atmosphere - which means that boiling will begin at almost 100 ° C. Here, if you go, then very carefully, without "pedaling." Otherwise …
… Here another housewife will kill me: “So what? The teapot, it’s boiling, doesn’t ask for food!”The mistress is mistaken. If all the water evaporates, then the teapot will end. And the motor, firstly, is much more expensive. Secondly, he is not only left without liquid, but also bring it to a boil - a taboo! After all, even a working cooling system in heavy conditions works at the limit of possibilities, when every little thing is important. It is bad if dirt or scale impedes the transfer of heat from the walls of the cooling jacket to the liquid washing them. But even worse, if the liquid boils: the heat sink from the walls to the vapor bubbles is negligible - the engine parts quickly overheat … Do not turn it off - serious damage may occur.
In fig. 2, borrowed from the textbook, shows a diagram of the fluid path and pressure plot in it. As you can see, the minimum is at the entrance to a working pump. It is very important that the first vapor bubbles do not form here, since they impair the operation of the pump - it is designed for liquid, not gas. A highly located expansion tank helps him in his work - he creates an additional support at the inlet. If the tank is empty - a shame to the owner. Leaking - also a shame!
But there are cooling system “jumps” of the coolest leaks of “Tosol”. Once a client arrived with a complaint: even in traffic jams, the motor does not overheat, but it’s worth over 100 km / h - hello! Stop - the bubbles gurgle in the expansion tank. Twice I changed the thermostat, then the radiator. Did not help. So he rushed to us.
At first they tried to imitate the "task", driving the motor in place, but even at high speeds it did not overheat. We realized that it was all about the load - it wasn’t in place. They removed the head of the block, examined both it and the gasket - and here is the culprit! See (photo 1) a “channel” left by hot gases? Here they burst at the maximum pressure in the combustion chamber - the bubbles disrupted both the heat transfer and the pump. Fortunately, the owner turned out to be a reasonable person, drove carefully - managed to avoid warping the head. Replaced the gasket and released in peace.
This is such a “trifle” - a gasket: it can severely undermine the owner’s budget. In the service, keep an eye out: if you arrived in the morning and they promise you to “boost” the engine by evening, run. It’s a pity one elderly Afghan disabled person caught on such a hook. I came to the service with a broken gasket - there they “bred” it by 16 thousand rubles for the overhaul of the VAZ 2106 engine. Allegedly, they did everything in a few hours - they squandered the block, polished the crankshaft, etc. And an experienced soldier believed!
And after about a month and a half the motor started to rush, and the gullible man went to another service. There he was again convinced of the need for repairs in full. This time the case resulted in 17 thousand. After some time, the owner felt something was amiss and came to us with a request to “stretch out” his head. We tried - and then we found a bolt that was spinning strangely in the block. Something with a thread? It is necessary to remove the head. That's when the locksmith suffered! The bolts seemed to be tightened with a wrench with a two-meter pipe - try turn it away! And the one that spun freely is shown in photo 2.