Besides the gear shift knobs, there are other areas of the car that might fit a lady's fancy. While in college I drove a sport's car which had raised lights in the front with the hood shaped with aerodynamic humps just behind the lights. These were about the size and shape of a man's thigh and hey, it seems a fun way to bump and grind yourself to a wonderful orgasm. Other vehicles may have similar humps and curves that may fit perfectly to a woman's anatomy.
Now guys, it is a little tougher for us, but hey we can't let the ladies have all the fun. One of the sexiest things I have found in a few of my vehicles is the rubber seal that goes over the hand brake. The soft, pliant rubber folds around the brake lever with a long slit down the middle that curves at the top just like a woman. As long as you keep that rubber soft and pliant you can happily finger your wonderful car until it simply purrs. Unfortunately, the brake lever has already popped that cherry and unless you remove the rubber seal here you probably aren't getting your cock between these soft folds.
Speaking of folds you might try some your seats where the back rest comes into the seat portion. I know you've slipped your fingers into those slits looking for change and things. Depending upon your car's design and your body's flexibility, you might be able to slip your cock into this opening. If not, what about the rear armrest? All you have to do is slide your cock into the slit between your seatback and the armrest. If it's too tight a fit, then pull down the armrest and slide your cock underneath it. That plush fabric on your seats will tickle your fancy. Of course you'll want a good fabric or upholstery cleaner to get up the cum stains.
For you more adventurous guys you can try the fuel intake. Now you'll need some soft fabric to line the metal sides of the opening, but wow, throw one leg up on the back of the car and you can take your lady for a ride. While the small amount of cum you'll spurt into her most likely won't cause any problems, I would only try this one time on a tank of gas. You don't want too much semen gumming up your lover's works.
Of course for those of you into doggie style, there is always the tailpipe. Caution, don't try this if your car is hot and bothered already. No, you need your car cold or you are going to have a lot of explaining to do at the emergency room. Anyway, the tailpipe will be dirty and rough so once again you'll want to line it with some type of soft fabric. Nice thing about coming into the tailpipe, you don't have to worry about your cum messing up the engine. No, you take your car from behind and you can cum and cum and cum.
Now there are other possibilities like sliding your cock between the weather-stripping on doors or trunks, but be careful here, one good hard thrust and you may close the door all the way. That's a pinch you'll never forget.
Anyway, if you practice safe sex and follow my advice you may find making love to your car an incredible experience. And hey, if you have any other ideas here, please leave a comment, I have a lovely Nissan just craving my attention. I'm sure she'll be ready for anything you might recommend.