Probably your sense of hearing. You probably detect subtle differences in the sound of the engine.

Back when I drove a pickup truck all the time I did have one time when I took it to a garage with a complaint that the steering was getting “sloppy”. They had it up on the rack and in no time at all told me that I was probably a few miles from having the linkage to the tie rod wear through and break, which would have let my front wheels turn at will. Not a good place to be in.

I recall that I also noticed during an oil change (which I always did myself) that the motor mounts had eroded to not much of anything before that became a huge issue, too.

But other than hearing or feeling something – which you can then describe, or being familiar enough when looking under the hood (or at the bottom of the vehicle) to say, “that doesn’t look right”, there is no sixth sense involved.

Familiarity with the vehicle helps, too. I gave that truck to my father-in-law with 205,000 miles on it.

@marinelife could well be. Driving on the highway, not long ago, at 75 mph I said to my SO “something feels wrong” and immediately started pulling off the road. Got down to about 35 when the front passenger tire blew apart but at that speed I was able to control it. Hate to think what it would have been like to lose the tire at high speeds. When I looked back on it, it was the sound of the tire on the road that I had alerted me. I did not notice any vibration as you would expect. My wife did not notice anything different until the blam and we were on the rim.

One day my Acura gave a loud pop while on the highway. I knew that was bad, and pulled off right away. Total power loss in the next few seconds. By then I was on the shoulder.

You feel vibration, hear a different sound spectrum, and feel a difference in performance.
We make engine health monitoring devices that do the same thing.

If you can lose a lot of weight and shrink yourself down to the size of a stack of dimes, with a little practice you can become a transducer.

If I couldn’t, I’ve owned at least four cars that would’ve killed me outright.

@LuckyGuy Pretty much. That is why I hate American mid/full-sized cars; the drivers seat is too isolated from road noise, engine noise, or lateral G-forces to know what the car is doing.

@jerv – the couch on wheels!

Our bodies are just big bony brains. It’s good to read these stories of jellies who have listened to them.

A week or so ago I pulled over soon after I’d merged onto a major highway because there was a shuddering feeling, and my neighbor, who was not far behind me for no special reason, pulled over in front of me about a quarter mile and started texting me as I worked my way around the car inspecting (that is, kicking) the tires. “What’s the matter, what’s the matter? Are you okay?” “Um yes. It was shuddering because a back window was open and had begun whipping the back-seat seatbelt back and forth. Plplplplplplplplplplplpl! Scared the crap out of me.” Drove home. Neighbor made fun of me. Shouldn’t have. He didn’t hear that horrid sound. That was my job.

You have to know and feel it in all senses. Mostly sound, feel & sight.
Any little thing could be tied to it. Gauges are good to have. Noticing a shimmy. The feel of how it brakes or accelerates. Once you get the feeling of it, you can tell when something is different.

In a way it is like a relationship. Pay attention to details, listen, notice changes and act on these signs. If you don’t, you may find yourself dead on the side of the road.

@blueiiznh Or, if you are lucky, you will find yourself alive on the side of the road with a dead car. Busted tie-rod ends are no joke!

I notice different noises sometimes. So in order not to obsess about it, I turn up the radio! Works every time.

I really like @susanc‘s explanation that our bodies are just big bony brains. What we hear and feel is transmitted from the ‘big bony brain’ to the actual brain, which thinks on it (whether we are conscious of it or not). Might send us a little warning if it’s concerned about it.