Engine cooling in Mazda 3.
Turbine cooling – slightly reverse procedure, exhaust gases are not the coldest, so the turbine absorbs a large part of the temperature, sometimes, that it literally glows cherry red or red-orange while driving (exceeds 500°C!). If we stop the engine without the turbo cooling down – the oil evaporates almost immediately, the turbine shaft is wearing quite clearly. Nay – oil also carries “garbage”, which, after rapid evaporation, remain on the axle, causing even more pitting. Nay – when we come in the morning and start the car – the residue on the axle will get pushed under the seals and start to wear them out – in this way “season” turbine, which “soon” it will leak and shed oil (to exhale, into the air and everywhere around). Moreover, after turning off the engine, the heated turbine burns the oil, causing the cross-section of the oil channels to decrease – resulting in seizure. Cooling down the turbine involves running the engine at idle speed “while”. It is accepted, that it's like that 2 minutes of idle speed (officially the minimum 30-60 sek). We are already reaching the house, We rush to the spot (taking it easy, of course), we limp, we limp, we park calmly, we turn off the radio, we collect all this, what to take in the car, (we block the gears with a bear-lock if anyone has one) we scratch our heads etc. Finally, we turn off the engine – For me it lasts 2,5 minutes. It takes practice.
There is one exception to this rule – Mazda engine “comprex”, which is the only one that does not require cooling of the turbine (you can and should turn it off immediately). The engine warm-up process remains the same.
If someone wants to play a prank on my husband and kill his turbo in a brand new car, after starting the cold engine, please hit the gas hard right away., high revs, sprint as per 400 m, and at the end of the ride – just make a little effort and then turn it off straight from high revs. The effect is surefire – the turbine will fall apart before 50,000 miles.
It is a common misconception, that the turbine “turns on” by 2000 revolutions. As long as the crankshaft is turning – this is how long the turbine also rotates. Effect “switching on” turbos result from the physics/chemistry of combustion and the actual pressure difference. As long as the pressure on the turbine does not exceed a certain level, you can even tell, that the engine is naturally aspirated. THE TURBINE IS ALWAYS ROTATING, when there are exhaust fumes (it is located on the exhaust manifold, So “collects” any exhaust from the cylinders).
During engine braking, the injectors do not deliver fuel (ropki) but the cylinders are ventilated anyway (the valves open, sucking in air, the engine compresses air, exhaust valves release), otherwise the engine would not brake! More or less compressed air is pushed out through the valves and drives the turbine even without burning fuel.
Turbine in DiTD (both engine models) is oil-cooled and water-cooled (circulation from the engine), both versions have a constant rotor geometry, only the bypass valve is controlled differently – either overpressure or underpressure.