2 habits that seem bad for the car and that Javier Sendín defends

Starting the car with the heater on doesn’t cause any damage. Javier Sendín, chosen in 2023 as the best mechanic in Spain, explains it without drama: the climate control system in modern vehicles already regulates the compressor’s work on its own. And this, no matter how much it sounds like workshop heresy, is more normal than it seems.

The cliché says one thing. Real mechanics say another. And here is the detail that matters: keeping the compressor active from time to time can extend the system’s life, while frequently driving on reserve fuel can indeed bring bad news.

Javier Sendín and the heating myth: what really happens

This matters to the reader because many still associate heating with an absurd overload on the engine. But in a current car, when you turn up the temperature, you’re not demanding a savage effort; you’re activating an electronic management system that distributes the workload as best it can. And that’s it.

Modern climate control doesn’t work like before

Sendín sums it up with a clear idea: current compressors are no longer “all or nothing” type. They are volumetric or variable displacement, meaning they can adapt their effort to actual demand. Less mechanical histrionics. More efficiency.

And here is the point many drivers overlook. If the compressor stays off too long, the O-rings can dry out from lack of gas and lubricant circulation. Human translation: the system quietly gets mad, and over the months, a leak or a costly malfunction can appear.

Why it can even be beneficial

An independent mechanic consulted for this type of case, a common observation in workshops, says almost jokingly: “what isn’t used, suffers”. And it makes sense. Running the system regularly helps distribute the oil and keep the whole unit in better condition.

The key isn’t to turn the heater on for the sake of suffering, but to understand that the system is designed to work as a whole. No heroics, no quirks. The car isn’t a museum piece.

When the reserve can actually cost you

This is where the message changes tone. Because, if the heater isn’t a big deal, often running on low fuel can cause real problems. And not small ones. Sendín warns that the filter can accumulate impurities and sediments from the tank bottom, which reduces flow and can affect engine performance.

For those who make short trips in Barcelona, on the C-58 or the Litoral ring road, this is especially a bad idea: stop and go, heat, vibrations, and an engine running with an almost empty tank. The perfect combo to cause trouble. Great deal, right?

What happens inside the tank when you run too low

When the level drops to the point of causing irregular vehicle operation, the risk increases. And if it stops, the damage can go straight to the injection system. In modern Common Rail systems, which operate at pressures of up to 2,000 bars, the fuel not only powers the engine: it also lubricates.

If that supply is missing, internal parts can suffer premature wear or even seizure. That is: a seemingly harmless mistake today can end up turning into a very unpleasant bill tomorrow.

The reserve is not a lifesaver

The romantic idea of “I’ll make it to the gas station” doesn’t hold up when the tank is dry. The car gains nothing from this improvised epic, and neither does the driver. Not at all. Better to refuel before the red light becomes routine.

In an interview with Mundo Deportivo updated on July 8, 2026, Sendín also recalled that modern mechanics don’t forgive bad repeated habits as much as before. And a climate control technician consulted the same month added a practical idea: if the system is used regularly, it works more smoothly and gives fewer scares.

What you should remember before putting on more miles

The reader is left with two useful and very down-to-earth ideas. First: starting the car with the heater on is not harmful. Second: running on reserve can indeed punish the fuel system and injection. And that difference is no minor detail.

Javier Sendín, Spain’s best mechanic in 2023, emphasizes this with a very straightforward reading: modern cars are designed to better manage certain loads, but not to endure bad habits forever. So, if today you have to choose between the sensor’s peace of mind and the temptation of reserve, the reality is the car appreciates the first much more than the second.