An engine is meant to be used, not abused and not babied.
Dylan Bowerman
The tachometer is a wonderful thing. Knowing how it works and how your car reacts at certain points across it will enable you to better communicate with your car. By understanding what it needs and how to best accommodate that, you can improve your driving, your fuel efficiency, and more.
Don’t baby the engine.
Most cars can get you from A to B without ever exceeding 3000 RPM. This becomes even easier with variable transmission technology (like a CVT). This makes it easy to not realize that there are benefits to a hot engine. Yes, I recognize that a running combustion engine is always hot, but it can be hotter at some times than others. Broadly, it is hotter when it is working harder.
Hotter temperatures can burn away at some of the contaminants that may have built up in the engine, like particles that made it past the filter or carbon that builds up from the combustion process. Thus, I hold that getting the engine to just under redline and holding it there for a small bit (just a few seconds) could keep it running well.
Don’t abuse the engine.
Designers spent a good while designing the engine. It is one of few components designed to last the entire life of the car. That is to say, in many cases, once the engine dies, the entire car is disposed of with it. Part of this designing was to calculate how fast the engine can run without breaking. This is marked on most tachometers by a red coloring at the values you should not reach, called the redline.
The redline on this car is at 6,600 RPM, but the engine is running at 7,151 RPM. This is called “redlining” the engine, and I highly recommend against it.
By running an engine at or above the redline, you are operating it beyond the capacity for which it was designed. This can lead to anything from unnecessary wear and stress, all the way to the engine’s mechanical failure. I always recommend that vehicle owners never redline their car unless they are acutely aware of the consequences that could befall them.
Many cars have features (whether electronic, mechanical, or both) that prevent the driver from redlining the engine. Automatic transmission cars will usually force an upshift at redline, even if the car supports an “auto stick” type feature, wherein the driver can influence the gear the car is using. This is done to prevent engine damage.
As a backup to that (and the first line of defense for most manual transmission vehicles), many cars will stop the transmission of fuel to the engine if it is running too fast, by disabling the fuel pump. This will cause the engine to temporarily slow down (since it has no fuel), which can prevent engine damage. If the condition causing the engine to race persists (such as the accelerator pedal being fully depressed or the vehicle being in too low of a gear for the speed), the engine will speed back up once the fuel pump is re-enabled, causing a cycle where the engine redlines, slows, redlines, slows, and so on. This behavior both protects the engine and alerts the driver to a hazardous condition.