A very common problem for many drivers, when temperatures start to drop, is the car’s engine simply refusing to start: you turn the key, the dashboard lights up, but the engine doesn’t have the power to start.
This happens because, on freezing mornings, the vehicles’ electrical system is pushed to the extreme, and the lack of precaution the night before takes a heavy toll. But, after all, is the cold really capable of stealing a vehicle’s charge overnight?
To understand what’s going on under the hood and find out how to prevent this headache, CNN Brazil spoke with mechanic Renê Rubbo Jr. He clarifies that the freezing climate attacks the system on two simultaneous fronts: it harms the engine’s functioning and weakens the energy source.
The specialist details the most common mistakes made by drivers on cold days, precautions in traffic and what should be done to extend the useful life of the equipment.
Thermal impact: why is the cold the biggest villain?
The belief that weather affects electricity is not an urban myth. Temperature directly influences the internal chemistry of automotive components. “One of the reasons is that every combustion vehicle, whether gasoline or alcohol, has difficulty operating at low temperatures; therefore, the engine has to work harder to run”, explains Rubbo.
In addition to the extra effort required by the engine, the energy source itself suffers a sudden drop in performance. The mechanic highlights that “the electrical reaction generated by the battery by its components tends to lose efficiency both at low and high temperatures.” The impact is measurable: “At very low temperatures, close to 0°C, there may be a loss of power of 20% to 30%, with this loss being slightly smaller at temperatures above 40°C, approximately 15%.”
It is exactly because of this thermal sensitivity that the automotive industry changed the design of several models. “That’s why many cars no longer have the battery in the engine compartment, but in the boot, under the seat, to keep the temperature more constant”, he points out.
Distress signals and the 2-minute trick
The car rarely stops running without first giving some kind of warning. The secret is to pay attention to details when starting up. “Normally you can notice that the engine is no longer able to turn the engine. In certain cases, on a second attempt, the engine is no longer able to turn”, warns the mechanic.
If the driver notices this slowness when arriving home at the end of the day, there is a workshop trick to avoid a blackout the next morning. But there is a way to try to get around this.
“Before turning off the car, turn off all energy-consuming components, such as headlights and taillights, air conditioning and others, the idea is to keep the car accelerated to around 1500 revolutions for a period of approximately 2 minutes, so that the alternator can survive for starting the next day”.
Phantom consumption and the risk of the “open tap”
Leaving accessories connected with the engine off is a primary but very common mistake. The expert makes the following analogy: “Using energy consumers is the equivalent of leaving the tap open: one day the water will run out”, he compares.
However, the danger also lies in cars that sit in the garage for many days, especially the more technological models. “This depends on each car. Older cars, with less electronics, suffer less from this problem, but newer cars, where the onboard electronics are very large, there are even cases where some already have an auxiliary battery”, explains Renê. This occurs because “some components do not turn off completely, thus generating a small consumption at rest”.
For those who drive little, starting the car for a few minutes in the garage helps, as long as everything is turned off. However, the mechanic suggests a more definitive solution: “What I recommend to customers who don’t ride much is to buy a device that is very common for motorcyclists, a ‘battery saver‘, which maintains, in the case of good quality devices, almost a simulation of battery use”.
Heavy traffic and alternator dangers
The useful life of the electrical system depends not only on energy storage, but on the car’s ability to replace this charge through the alternator. The problem is that, between cities, this account often doesn’t close.
“In case of traffic jams, I recommend turning off the lights and keeping only the lights on, in extreme cases even turning off the air conditioning. With the engine idling you end up consuming more energy than the alternator can generate. After all, it depends on the engine speed to generate energy”, warns the specialist.
“Vehicles that travel in heavy traffic every day tend to have a shorter battery life than those that drive more on roads.”
The relationship between the components requires attention to the warnings on the panel, which often go unnoticed. “A precaution that few people take is, when they turn on the car key, to check if the one on the dashboard is lit. Many cars have a problem with the alternator and the light doesn’t come on; you start the car and end up stalling halfway”, warns the expert.
In some cases, a faulty alternator can generate excessive current and damage the storage, or the reverse: a shorted part can draw so much current that it ends up overheating and burning out the alternator.
After all, charging solves the problem or is it time to change?
When the car finally “dies”, the classic dilemma arises: call for help to recharge () or buy a new part? The answer depends on the equipment’s history.
“When the battery is relatively new and discharged by a component that was left on, recharging is correct. But when it is beyond the period covered by the warranty, the best option is to replace it”, advises the mechanic.
Although modern versions are mostly sealed, Renê remembers that in models where it is still possible to check the level of the solution and top up with distilled water, “it is very common to have survival with refilling”.
