The short answer is, yes they do, and for the most part negatively. Depending on the car but especially the buyer, modifications can significantly hurt the resale value because simply put, cars are built to spec for a reason. The original parts fit correctly because they were made to. The engines, brakes, suspension, frame and tires are all chosen, made and tuned for specific attributes that the manufacturer decided on years in advance. Modifying a car destroys the design integrity of the car, and unless done properly, can do much more damage. For instance, you may want to make your car faster by changing some things on the engine, engine modifications that change the air/fuel ratios may make the engine run lean (not enough fuel), or rich (too much fuel), while either one causes long term damage.
Not necessarily, there are certainly some rare and circumstantial exceptions to this rule. Let’s say you have a Corolla, but it’s been modified to be a race car (probably to the extent where it’s no longer a Corolla). For someone looking for a good commuting normal Corolla, your car is worthless, because of the modifications. The flip side is someone who is looking for a racing Corolla will be thrilled with your car.
By modifying the car, you’re narrowing down the potential market, and this is true for style modifications, performance and any other kind of modification. The next owner may not want a giant stereo system, especially if it complicates the car’s electrical system and the same goes for aftermarket alarms. This might sound like it’s making the car safer, but the truth is if the car was not built with an alarm system in mind, installing an aftermarket one might cause horrific electrical problems.
Besides for racing, there are modifications that seem more stylish and fun. For instance, you can fit little TVs in the headrests (if you so choose), and it could up the value but only to the right buyer. A different buyer may see this modification from the side of someone who wants to avoid any extra potential electrical problems. The same can be said of aftermarket alarms. Someone may turn down buying a particular car with an aftermarket alarm because they don’t want to deal with whatever problems the car may have as a result because the car simply was not built with an alarm.
Modifications that have to do with performance are not good for resale in general, neither are style modifications. Are there any modifications that can be done to increase resale value? The answer is maybe, but it depends.
Modifications that take existing parts and improve on them could be looked at as worthwhile investments. For instance, the thermostat housing on a late ‘90s 3 series BMW is made out of plastic. These cars are notorious for failing cooling systems, so replacing that plastic thermostat housing with one made of metal, depending on who you talk to, could be considered an example of a good modification that you can do to improve the vehicle. A part of that car that is generally not up for debate is the impeller on the water pump, which is also made of plastic from the factory. A water pump with a metal impeller might be another good modification as well.
If you really want to modify your car, don’t throw out the old parts and in fact, if you plan to modify your car heavily or otherwise, it might be a good idea to keep the car around for a long time. Check out the history of your car, as in recalls and parts that frequently fail, and try to get better replacement parts. Using the late ‘90s BMWs as another example, they have a hard time holding on to front lower control arm bushings, so replacing these with better quality may be a good modification.
A good modification in general, for any type of car, is a better braking system. Switching to better pads like ceramic or metallic alone will improve stopping power, and switching to cross-drilled and slotted rotors are a good idea as well. Be sure to have a shop do your brakes, as this is one of the most important parts of the car you don’t want to make a mistake on. Make sure the parts fit and are built for your specific vehicle.
Be sure to do research before you modify, and make sure the parts you’re replacing are a genuine fit, and if your car manufacturer made better parts later that didn’t make it into your vehicle, use those. OEM (Original Equipment Manufacturer) parts are always the best fit, because those parts were made for your specific vehicle. If you decide to make these changes to your car by yourself in your own driveway, be sure to have a mechanic double check your work.
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