The gear shift indicator, a silent killer for your car's engine
Modern vehicles come with an indicator that advises you when to change gears, whether to upshift or downshift. However, none of them do their job well.
If you own or have driven a relatively modern vehicle, it almost certainly has a gear shift indicator on the dashboard.
It is an icon that alerts you when you should upshift or downshift, or alternatively, a number indicating the appropriate gear for each moment. But, have you tried to strictly follow those recommendations? If so, you have likely noticed that something doesn't fit.
The combustion is not fully completed, which generates soot that accumulates in pistons, EGR valve, and particulate filter
What the gear shift indicator should serve for and what it really does
In theory, your vehicle's gear shift indicator helps you maintain the proper gear ratio based on the speed and the pressure you apply on the accelerator.
To achieve this goal, the control unit should take into account fuel consumption, the accelerator response, and also the long-term care of the engine. Unfortunately, manufacturers only seek one thing: to send you the message that you should consume —and pollute— as little as possible.
To achieve this, your vehicle's gear shift indicator —and that of all others— advises you to upshift at a ridiculously low engine RPM. And this has consequences, most of them negative for you, who ultimately are the one who bought the car and needs it to last many years.
Why shifting gears at low RPM is a huge mistake
Manufacturers have become true tightrope walkers of regulations. To pass emissions and consumption tests, the software that governs that little icon on the dashboard is programmed with one goal: to reduce average consumption during the homologation cycle, not to take care of your iron and aluminum block.
That’s why the indicator asks you to upshift when the engine barely exceeds 1,500 RPM. It looks great on the lab sheet; in real life, it’s like forcing a cyclist to climb a hors categorie hill in a big gear: not only is it ineffective, but in the long run, injuries are guaranteed.
Vibrations, soot, and other ghosts that homologation doesn’t account for
An engine that operates below its optimal RPM struggles to provide the power you demand through the accelerator pedal. This, cruising at a constant speed, is not a problem and is even advisable to reduce consumption.
But, the moment the car needs to accelerate on an incline or to overtake, micro-vibrations occur that end up transmitting to bearings, supports, and the crankshaft itself.
Not only that, but the combustion is not fully completed, which generates soot that accumulates in pistons, EGR valve, and particulate filter. Other things that can happen are that the alternator charges less and the battery ages faster.
None of this is taken into account by the manufacturer who, on the other hand, emphasizes that you follow the maintenance manual (€€€€€€€€€), but any veteran mechanic will confirm: cars that always run choked and low on RPM end up in the shop sooner than expected.
When the ear commands more than the indicator
Engineers of the past knew that an attentive driver is the best sensor. If the engine responds sluggishly, vibrates, or sounds like it’s complaining, it’s time to downshift, even if the green icon says otherwise.
As a general recommendation, your vehicle's engine should always operate in the following RPM range:
- Gasoline: between 2,000 and 4,000 RPM, where the air-fuel mixture burns cleanly.
- Diesel: between 1,700 and 2,500 RPM, with enough torque to avoid strain.
Even more importantly: the appropriate gear is the one that allows you to accelerate without flooring the pedal. That is true economy. And yes, it is undeniable that higher RPM means greater consumption.
But it also means more breakdowns or an RPM so low that the engine lacks the power to respond. In fact, this is one of the reasons why many low-power cars (60-70 HP) have homologated consumption higher than their 80-90 HP counterparts.
Real-life example
Imagine a roundabout in fourth gear. You exit, press the accelerator, and the car responds with a vibration that seems to plead for mercy. That is not efficiency; it’s an engine begging you to downshift to third. Ignoring that plea is like training with 'sneakers' for a marathon: cheap today, expensive —and painful— tomorrow.
The best thing you can do is start by learning the RPM range your engine needs depending on whether it’s gasoline or diesel. And from there, get used to listening to and feeling your engine. You should feel it agile and energetic, not sluggish or suffocated. Over time, it will come naturally, and you will only need intuition to shift gears.
The dashboard gives you one piece of information; your experience decides whether it’s time to upshift or downshift (also depending on the road conditions at that moment). Thus, savings will not only be at the gas station but also at the workshop.
