Ep 14. Dirty vs. Clean Car

In season 7 episode 14 of Mythbusters, the team takes on the age-old question of whether a dirty car uses more fuel than a clean one. In this episode named Dirty vs. Clean Car, Adam Savage and Jamie Hyneman explore the truth behind this common belief.

To tackle this myth, Adam and Jamie first needed to establish a baseline. They start by installing a fuel meter in a car and driving it on a course, creating a control group with no exterior modifications. They then take two identical cars and cover one in dirt, mud, and grime while keeping the other one clean and polished. After ensuring that both cars weigh and perform similarly, they hit the streets for a test drive.

The Mythbusters team soon discovers that there are many factors at play when it comes to fuel efficiency. One significant contributor is air resistance, which can result from anything that protrudes from the car surface. As the team expected, the dirty car suffered from more air resistance than the clean one, which translated into lower fuel efficiency.

Next, they put the two cars through a series of tests to measure their fuel consumption accurately. In their first attempt, they let the cars idle to see which one burned through gas faster. They found that the dirty car used a little more fuel than the clean one, but the difference was too minuscule to be a significant factor for the average driver.

Adam and Jamie then took the cars out on the open road and had them drive at a constant speed of 65 miles per hour. They had the same results as the previous test; the dirty car used slightly more fuel but not enough to justify frequent car washes.

The team's final test involved driving the cars up and down a hilly terrain. To make the test more realistic, they loaded each vehicle with two passengers and bags of sand to simulate real-life driving conditions. The results showed that the dirty car used 10 to 12% more fuel than the clean one on the uphill drive, confirming that air resistance was the primary culprit.

Despite their findings, the Mythbusters team acknowledges that there are many variables involved in fuel efficiency. Factors such as driving style, traffic conditions, and car maintenance all play a role in determining how much gas a car will use. Therefore, while keeping the car clean may help with air resistance, it is not a significant enough factor to warrant washing your vehicle every week.

Aside from tackling the myth, one of the highlights of the episode is when Adam and Jamie take cleaning a car to the extreme. They test out several wacky cleaning methods, such as blasting a car with a fire hose, scrubbing it with a giant brush, and even wiping it with human hair. While some methods are silly and ineffective, others yield impressive results.

Overall, the Mythbusters team puts another long-standing myth to the test with their signature wit and humor. They demonstrate that while a clean car may look better, dirt and grime on the surface do not significantly impact fuel efficiency in most cases.