Dumb Things Drivers Do to Their Cars

Some people make a lot of mistakes with their cars. Not on purpose, but because they just don’t know the damage that can be done when assuming certain, simple things about their vehicles. Here are five particularly dumb things drivers should NOT do to their cars.

Gasoline in a Diesel
Putting any amount of gasoline in a diesel-powered vehicle is either an expensive mistake or a very expensive mistake. If you realize your screw-up before you start the vehicle, it’ll “just” require having the vehicle towed to a dealership, draining the tank, draining and cleaning the fuel line from the tank to the high pressure pump, draining the fuel filter, replacing the filter then running the bleeding procedure three times with a scanning tool, said Volkswagen’s Jim Gill. If you start the engine after putting any gas in a diesel “catastrophic failure will occur,” said Gill. “Nobody can tell you when, but it is not a long time or distance.” The damage is sure to occur because, unlike a gas engine, a diesel engine uses the fuel to lubricate parts, including the fuel pump, injector nozzles, and even the piston rings. People are sure to make the mistake of putting gasoline in a diesel vehicle because a gasoline pump nozzle will easily insert into a diesel’s tank opening. (The diesel nozzle is too big to fit in a gas car’s opening.) The takeaway: If you’re going to loan your diesel vehicle to your brother-in-law, first install a locking fuel cap.

The Burn-It-Off-Oil Change
This is when you drive until the oil light comes on then fill the engine with fresh oil. The car did its own oil change! Well, not really. What’s left behind in the oil pan is a thick layer of sludge. And the oil filter is so clogged with gunk, most of the oil bypasses it. Sooner or later, the oil pickup will ingest some of the residue at the bottom of the pan. It’ll be pumped directly into the engine (bypassing the clogged oil filter) where it’ll block an oil passageway. What’s on the other end of that oil passage won’t get lubrication and will soon tear itself apart. If you’ve been guilty of the burn-it-off oil change, here’s your penance: First, change your oil (and filter) and drive the car for 30 minutes. Then change the oil and filter again. Drive for 30 minutes and change the oil and filter. Repeat this process until the draining oil appears new. Then change your oil again in about 1,000 miles. You may require a mechanic to take off the oil pan and clean out the gunk, if it’s really bad.

Regular Gas in a Premium-Fuel Car
Times are tough, so perhaps you’ve thought of saving a few pennies by using regular gas in a car that calls for premium. Instead of saving money, you may be wasting it, says Charles Hubbard of Lexus College. While this may not be true for all cars that call for premium, Hubbard says using 87-octane fuel in Lexus vehicles that require 91 Octane will reduce fuel mileage by about six miles per gallon—which will more that offset the lower purchase price of regular gas. Hubbard says the lower mileage occurs partially because the lower-octane fuel requires the engine to work harder to achieve the same performance. Try it for yourself to find out if your vehicle gets worse mileage on regular. A useful test requires running two or three tanks full of fuel through the vehicle, and careful measurement. When you switch back to premium, the mileage improvement won’t occur until after a couple of tanks of 91 Octane.

New Tires on the Front
When replacing only two tires, it’s tempting but dangerous to put them on the front. If you run into a deep puddle of water, the new front tires will easily slice right through, while the half-worn rears will hydroplane. The water will literally lift them completely off the pavement, if, that is, the water’s deep, you’re going fast, or the rear tire pressure is low. If you have new tires on the front and half-worn ones on the rear, when you hit a puddle in a corner the car will spin out faster than you can say, “Officer, I don’t know what happened. It just spun out.” For tire-company demonstrations, I’ve been a passenger while about 10,000 people spun out in a car with new tires on the front and half-worn tires on the rear, so trust me on this. This is true for front-, rear- or all-wheel-drive vehicles.