“Turn it on, wind it up, blow it out” - Ronnie and the Daytonas, Little GTO .
On a test drive of a used car at a dealership, drive as close to the limits as you feel comfortable with. Good tests include:
-Slide it around an empty parking lot and see what happens on turn-in, mid-corner, and corner exit under power, under trailing throttle, and under braking. You want a predictable car with high enough limits that you have something in reserve for an emergency maneuver. Switch any stability control off for this.
-Do a full-throttle takeoff from a stoplight. You want something that can get you in front of another car in case you ended up in the wrong lane for what you need to do at the next light.
-Do a full-power blast from 50 to 100 miles per hour. If this takes more than you feel you can find the room to do safely then the car isn’t fast enough. The faster you’re going, the less time you’re exposed to danger when you’re passing somebody.
-Turn the stereo and climate control off and drive down a bumpy, hilly, twisty road. If you hear rattling and squeaking, then the body might not be stiff enough to prevent the car from shaking itself apart over the next 150,000 miles.
-Get into a clear area and stand on the brakes from 100 miles per hour (see above point about not buying a car that can’t reach what’ll be a normal highway speed in a few years). Do the brakes fade? Does the car try to drive itself off the road crown? Are there any other quirks?
-Does the gearlever move smoothly from gear to gear? Does the clutch slip? Is there any slack in the steering?
-What does it look like under the hood? Are there any cracks in the hoses? Are the belts properly tensioned? Is there water in the oil? Does it look like the oil’s been freshly changed to hide something? If so, is there oil in the coolant? Are the CV joint boots cracked? Are the brake discs worn unevenly? Has the tire tread worn evenly? How does the insulation look on the ignition wires? Is there any corrosion on the battery terminals? Do the shocks work? Does the car move smoothly up and down when you push on the bumper?
If you’re trying out a new car, there are a couple changes. You shouldn’t have to do an underhood inspection. Ask the dealer if you can try their demonstrator or a pre-owned car that’s the same model - explain that you intend to give the car an honest shakedown on the test drive and don’t want somebody else’s new car getting broken in improperly. If the salesman comes along, ignore him completely. Just tune him out. You should definitely not let him influence or dictate the route. If he doesn’t want to ride along for the parking lot testing, then he can watch from the edge of the lot. If he gets scared during the test drive, remind him that the seats are Scotchgarded (they are, right?).