The Truth About Rats and Car Engines

Few species are more reviled than rats. The mere sight of one can trigger gasps and shrieks. Prolific eaters and prolific procreators, rats are associated with disease, rot, filth, death, and impending doom in horror movies. These highly social and surprisingly intelligent rodents, however, are rarely mentioned in the same sentence as car engines — but many motorists discovered during the pandemic that a car engine is exactly where the real-life horror takes place. As a result, the world's most infamous rodent has somehow managed to make itself even more loathed in the public imagination.

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The world's most maligned mammal is also its most populous. With more than 60 different kinds of rat, some of which can grow up to 30 inches long, no other species of mammal can claim more members. There are an estimated 2 billion rats in China alone, and although no one knows for sure how many make their home in the United States, governments in cities such as Chicago get more than 50,000 rat-related calls in a year. Although they can spread diseases, these survivors are largely resistant to it. They have low mortality rates, they procreate incredibly quickly, and their reputation as ravenous, insatiable eaters is well-earned.

Starting at street level, rats can and do climb up car tires and crawl into the front wheel wells, through the brakes, and into the engines of vehicles. Once inside, the relationship between car and rat is not symbiotic. They can build nests, squirrel away food, and even have babies in the systems under the hood. Mostly, however, they chew. Rats can damage every kind of wire in a vehicle, which can trigger hard-to-detect system malfunctions and even make a dangerous fire more likely. Rats can burrow through the firewall between the engine and the vehicle's interior, leaving human passengers exposed to a rat-induced roasting. 

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In reality, the chance of rats causing a car fire is quite small, but unwelcome chewing is all but guaranteed. Rats' teeth grow continuously their whole lives, and they're genetically predisposed to constant chewing — even when not eating — to keep their teeth short and sharp. Automotive electrical wiring provides the perfect combination of firm but squishy protective coverings wrapped around hard metal wires within. Rats sharpen their teeth by chewing on things such as rocks and trees in the wild, but wires are a perfectly acceptable substitute in their oral health regimen.  

The rare rat found nesting in an engine isn't so rare anymore. According to reports from publications such as The New York Times and the Detroit Free Press, mechanics found a dramatic increase in mysterious mechanical failures traced eventually to rat-related damage and the pandemic. With its related shutdowns, millions of cars became mostly idle, offering a quiet, accessible, and human-free respite for gutter-weary rats looking for upgraded digs.

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Urban rats rely largely on the garbage thrown out by restaurants that closed or reduced output during the pandemic, and scraps thrown away by people who now stay home. With food sources removed and eating patterns disrupted, rats have been forced to look for food in places they otherwise might not have. 

It's common for rodents and other small animals to damage engines in winter under the best of circumstances. That's because they seek warmth in confined quarters when the weather outside gets rough. With food more scarce during the coldest months and more rats on the prowl, experts expect the problem to worsen when winter blows in. 

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Even larger rats can squeeze into incredibly tight spaces, which makes diagnosing rat-related engine damage tedious and time-consuming. The wiring they love to nibble on is intricate and can affect several different systems. The mechanics cited by The New York Times, Detroit Free Press, and other publications mostly agreed that rat damage almost always costs hundreds of dollars, and it's not uncommon for repairs to run into the four figures.

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Rodent-related damage is almost never covered under warranties, which means even if the car is covered by the manufacturer or dealership, rat victims are still out of luck. When it comes to insurance, the majority of cars suffer damage in the mid-hundreds, which usually falls within the driver's insurance deductible even if their provider does cover rodent damage.

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Petroleum has long been the traditional base for the rubbery and tantalizingly chewable protective coating that covers the countless wires found in a car's electrical system. Now, major automakers such as Toyota use more environmentally friendly wire insulation made not from crude oil byproducts, but from soybeans. Soy-coated wires can satisfy rats' notoriously ravenous hunger streak and their natural chewing fix at the same time — and they apparently love the stuff.

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In 2016, a group of Toyota lessees filed a class-action lawsuit that tried to force the automaker to cover rat-related damage under its warranties for vehicles with wires that were marinated in delicious soy. Two years later, Goliath smashed David as the court tossed the suit and judged Toyota to be blameless.

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Many people, including at least one of the Toyota plaintiffs, have reported rats as repeat offenders. As the stories go, rats squatted in the victims' engines and tore up the wiring. Their human hosts paid out hundreds of dollars — in at least one case, $1,500 — for repairs, only to have rats move right back into the engine and chew everything up again. 

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On its face, it's easy to write this topic off as unlikely outlier. But while the lawsuit was limited to the owners of specific Toyotas with soy-based wiring who leased their vehicles between 2012-2016, its lead attorney told the Detroit Free Press that his investigation revealed that "tens of thousands of drivers nationwide" were being nibbled into mechanics' shops by rats. One can only wonder how many victims without legal representation were vanquished by Templeton and his ilk.

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When they find a place they like, rats put down stakes and invite their friends, and all that commotion leaves telltale signs. Look for droppings and urine, as well as anything that looks like a nest or nesting materials, sticks, twigs, or small bones. Mechanics and victims alike have been alerted to the presence of rats after following the source of unusual warning lights coming on for no apparent reason, such as the fuel exhaust warning.

One of the best things you can do to prevent an engine from becoming a rat motel is simply to drive the car regularly, even if you don't have to. Long periods of stagnation are bad for cars anyway, and intermittent driving will make most rats seek out a softer and more stationary target. Even when you don't drive, look at and around the car regularly, popping the hood and looking for some of the clues. If you're really worried or you've spotted some potential squatters in the area, spray rodent repellent or peppermint oil on and around the front tires and wheel wells.

Related: 20 Ways You're Ruining Your Car and Don't Even Know It

Squirrels can cause havoc to your car too. One rascally squirrel in North Dakota stashed a whopping 42 gallons of black walnuts inside a man's Chevy Avalanche. Presumably hoarding food for winter, the little guy stuffed the engine compartment full, along with in and under body panels, and places that have probably not been discovered yet. The truck's owner had to dismantle the front end to get them out. No word on whether the squirrel ever recovered its stash.