If you direct fluid from the heater to the thermostat, the temperature in the engine and in the passenger compartment will be normal in winter and summer.


Probably, I was not the only one who thought about why, in our machines, a working cooling system when the heater is turned on in cold weather does not ensure the normal thermal regime of the engine without using various kinds of radiator heaters, throttle washers in the pipes, removing the fan impeller and other measures.

Almost all domestic cars have basically the same cooling system (Fig. 1, a) - with a lower thermostat, where it automatically maintains the temperature of the coolant within the specified limits. For example, in “Moskvich” 80–95 ° С, in front-wheel drive VAZs, “Oka”, “Tavria” 87–102 ° С, etc. The thermostat usually regularly performs this function in any frost (up to known limits), and in all engine operating modes … until the heater is turned on. What is the matter?

Consider the operation of the system. On the one hand, the radiator is a heater for the air entering the passenger compartment, and on the other hand, a fluid cooler. The heater is almost the same radiator as the main one, only smaller. From the main radiator, the cooled liquid enters the thermostat, and then through it goes to the engine to the water pump. Here it is mixed with chilled fluid from a heater. What then becomes its temperature? Explicitly lower. And the stronger the frost, the colder it is. A thermostat, it turns out, sideways in the literal and figurative sense. At this point, they usually put a cardboard or a cover on the radiator so that the liquid in it cools less.

For verification, I measured the temperature at two points: T1 - on the upper half of the thermostat housing, where the thermo-power element is located, and T2 - on the water pump housing (Fig. 2, a). The air temperature was about 0 °; the engine worked at 1500-1700 rpm of the crankshaft on a standing machine; the radiator electric fan was turned on, simulating an incoming air flow during movement; heater tap is closed.

The results confirmed the assumptions. At point T1, the temperature rises to 78 ° and remains constant with increasing speed of the crankshaft. At point T2, the temperature turned out to be the same - 78 °. The arrow of the standard liquid temperature indicator is in the middle of the white sector of the scale (normal). Therefore, the thermostat really maintains the set temperature - about 80 °. Now - the most interesting! He opened the heater tap. In less than two minutes, the temperature at point T2 dropped to 72 °. He turned on the heater fan for maximum rotation speed and opened the heater dampers for maximum air supply (as in severe frosts) - the temperature at point T2 dropped to 60 °. The arrow of the temperature gauge deviated to the left edge of the white sector of the scale. And at point T1 the full order is 78 °.

Bad situation. When the heater is on, liquid enters the engine 10–20 ° colder than necessary, and the engine operates under abnormal thermal conditions. Hence, along with a cold heater, carburetor malfunctions, slightly increased fuel consumption, etc. are possible.

Cardboards and other screens in front of the radiator in some modes help warm the engine, sometimes even too much. They, limiting heat transfer in the radiator, allow the main valve of the thermostat to fully open and supply liquid with a temperature above 95 °. Along the way, it mixes with cold from the heater and the engine receives a liquid of a more or less normal temperature. But this is with its small loads. As soon as they increase, there is a threat of overheating. In short, cardboard and other heaters sharply worsen the adaptability of the cooling system to various operating conditions.

The conclusion suggests itself: if the heater radiator introduces an imbalance in the operation of the cooling system, then something needs to be done with it. As for the fluid supply to the heater, everything is clear: it is taken from the hottest place in the engine. With its withdrawal, the question arises: why does cold liquid return directly to the engine? Can I send her somewhere else?

Can! The fluid from the heater must enter the thermostat, because it is he who controls the operation of the cooling system. But it is impossible to connect to any of the branch pipes leading to it (via a tee), since they are completely blocked by thermostat valves and the normal liquid circulation in the cooling system is disrupted. There remains the only possible option - to embed a new pipe in that part of the thermostat housing where the thermopower element is located. The best place is opposite the existing pipe and as close as possible to the housing connector, where the liquid will mix well (Fig. 2, b). So I did (in the photo). It was possible to solder the nozzle and plug the hole on the body of the water pump without much difficulty.

The difference between the converted system (Fig. 1, b) and the standard one is that one more stream, but only one, is added to the previous fluid flows that control the position of the thermostat valves and are regulated by them, which enter the thermostat. Both thermostats at the outlet should have the same fluid temperature.

Wanting to find out what happened after the alterations, he immediately took up the thermometer. The measurement conditions were the same as with a standard cooling system, but the results were completely different. After the engine was warmed up, the temperature at points T1 and T2 was 78 ° and remained so regardless of the operating modes of the engine, heater, and radiator fan. The arrow of the liquid temperature indicator stably stood in the middle of the white sector of the scale. To this we must add some positive subjective sensations: the engine became hotter to the touch, it worked without failures, it became hot in the cabin with the maximum supply of hot air, as in a bathhouse.

Now in winter you can forget about the heaters of the radiator - all kinds of cardboard boxes and covers. In the summer, there is no difference in the operation of the standard and modernized systems. In other words, a redesigned cooling system with a new thermostat is always ready to work in any heat and in any frost.

In conclusion, some tips. The greatest effect was obtained on cars with small engines in volume and power. That is, for all domestic models with their modest engines under severe operating conditions, such an alteration will be especially useful.

The cooling system with a lower thermostat has obvious, undeniable advantages over a system with an upper thermostat. Therefore, for those who have old models of Volga, Moskvich, IL, old foreign cars, I recommend redoing the cooling system as described in the article “Improving Veteran Cooling” (ЗР, 1997, No. 3) and in “Experienced Tips” ( ZR, 1996, No. 11). And of course, you need to install a redone thermostat.

A patent for the invention has been obtained for the proposed cooling system.

Fig. 1. Scheme of the standard (a) and converted (b) cooling systems of “Muscovites”, “Lada” and other cars: 1 - a thermostat; 2 - engine radiator; 3 - radiator fan; 4 - an expansion tank; 5 - temperature indicator sensor; 6 - coolant pump; 7 - engine cooling jacket; 8 - heater fan; 9 - heater radiator; 10 - heater tap; 11 - a stub; 12 - an additional branch pipe (from the thermostat VAZ 2108).