How to Keep Mice, Rats and Other Rodents out of Your Car Engine

Rochelle has experience with wild critters and gardening adventures while living the simple life in a rural area for 20 years.

Are Rodents in Your Vehicle?

Rodents are everywhere, and they can do considerable damage when they invade your vehicle. They might decide your car is a safe place to make a nest and a handy site to store food. If you can discourage them, you may win the battle.

There are dozens of techniques used to prevent mayhem by the destructive critters, and they work especially well in combination. Multiple lines of defense seem to work best.

Steps to Take

• Leave the hood up. Rodents are looking for a dark place to nest. This idea could help discourage nesting, but may not be the ultimate solution.
• Hide your dog food, cat food, and birdseed. Dog food is the gold standard of rat society. Rats will stuff pounds and pounds of it into the air cleaner, glove compartment, or other empty spaces in your car.
• Remove or seal off rat hiding places near the car. Cut down nearby thick shrubbery and vines where they can hide. If you have a garage, block rat-sized entrances to the building, or spray openings with substances that rats hate (see below).
• Block small entrances to the vehicle engine compartment. Some car owners place traps around the vehicle or on top of the wheels, since rats climb wheels to get into the engine. Some block engine openings with wire screen.
• Use electronic deterrent devices. Rodents can hear ultrasounds that we cannot, and it annoys them. Some learn to ignore it. Those with strobe lights like MouseBlocker or Rid-a-Rat may work for longer periods, as they disrupt the darkness that rats prefer.
• Make your engine and its entrances smell bad, at least to rats. Motorists have had success with peppermint oil, powdered fox urine, used cat litter, cat hair, dog hair, Pine-Sol, Irish Spring soap, red pepper, and laundry dryer sheets. The people who make Rataway tell you to spray it on all the wires in the engine.
• Do not let the car sit unused. Drive it once in a while to discourage rats from doing mechanical or electrical work.
• Finally: use traps to remove the rats who get through. The old-fashioned snap traps still work. Glue traps work too but may torture the rat. Humane cage traps may work, but relocating the varmints can be a temporary fix. Toxic baits do kill rats eventually, but are likely to also poison predators, including domestic animals and pets.

Some Techniques Work (For Some People, Some of the Time)

It is a myth that small autos are powered by hamsters running on exercise wheels, but it is an unfortunate fact that rodents can live and create mayhem in engine compartments. In fact, the damage done to vehicles by mice, rats, and their many cousins can be considerable.

Gnawing wires, ripping out insulation for nesting materials, or squirreling away caches of nuts and trash in car and truck engines can destroy some of man's most sophisticated transportation technology and cause significant financial loss.

This is especially true if you live in a rural area. You need your car to get to your job or to go shopping, but wood rats and other critters want it for their homes.

Rodents Can Move in Quickly

Rural people know that a seldom-used old car may be taken over by rodents, but the critters can also get excited about brand new cars. In less than 24 hours, they can destroy much of the wiring.

Some plastic insulating material now being used in cars seems especially tasty to the tiny invaders. When mice chew the insulation off wires that connect batteries, alternators, or anything electric to anything else, they cause short circuits that result in costly restoration.

After the repairs, mice may go back to work and cause the same problem again, unless you take steps to prevent them.

Mechanics See Engines Destroyed by Rodents

"Apparently they have nothing but time," says Rick LeDuc of Rick's Automotive Service in Mariposa, California. He has found elaborate nests in intake manifolds and even litters of tiny pink mice inside air cleaners stuffed with bedding material.

In one of the more ambitious nests, he found part of a broom handle that had been dragged into the inner workings, as well as "a couple of pounds of dog food." In another instance, he said that only the wires coated with blue plastic insulation had been gnawed.

"They are supposedly color-blind, but sometimes they pick out one certain color of wire to chew," he says. "Probably there's something about the taste or texture."

Several auto repair businesses report multiple incidents of rodent damage each month. The time of year doesn't seem to matter. Hoarding, nest building, and wire gnawing are year-round occupations.

Repair costs can be as high as $500 and sometimes much more. In at least one case, so much wiring damage was done that the car was not worth fixing.

City Mouse, Country Mouse

Rural car owners sometimes come into a repair shop complaining that they "smell something burning.” Such an odor may come from smoldering grass or pine needles tightly packed into a carefully fabricated nest, or from burning droppings, stashed food, pack-ratted items, or the deceased bodies of the actual culprits.

A lot of people are surprised to discover the source of their problems. Why are so many furry occupants living where they are not welcome? This is not their natural habitat. Are they planning to take over the planet by disabling our vehicles?

The real reason rodents seek a home under a hood is that it provides a dark, warm, secure place to hide . . . at least until the ignition key is turned. The start-up of the car’s machinery can be deadly for the critters, and sometimes can cause serious consequences for the drivers as well.

An acorn rolling into a crevice after a driver stepped on the gas pedal can keep the throttle open. The driver of a late model Ford truck was taken for a wild ride on a winding country road, and severely damaged his brakes before he could shut off the power.

The wood rat culprit apparently abandoned ship before the adventure, but his hoard of nuts almost caused a real disaster. The truck required towing and lots of professional attention.

Collecting and Nesting Behavior of Wood Rats

John Muir, the famous Yosemite naturalist, called the wood rat (or pack rat) "a handsome, interesting animal." In his detailed descriptions of Sierra flora and fauna, Muir also opined that "no rat or squirrel has so innocent a look, is so easily approached, or expresses such confidence in one's good intentions."

The comments of today's vehicle owners plagued by rodent motor damage are much less complimentary—and are often unprintable. It may have been easier for the poetic naturalist to appreciate the animal, since he usually traveled on foot, rather than by SUV.

Wood rats are notorious for accessorizing their nests with things they collect, ranging from natural curiosities like bones, cones, and stones, to the tools, trash and treasures furnished by humans. Muir recorded incidents of rats stealing combs, nails, tin cups, eating utensils, and spectacles, which he supposed were used to strengthen rat nests.

Once inside an engine compartment, the rats see a mother lode of wonderful man-made objects, with wires and hoses and tubes connected to a spectacular variety of shiny metal and plastic components. To this assemblage, they will add their acorns, pine needles, hardware items, bottle caps, and whatever ornaments suit their eclectic decorating style.

Even before the era of motorized vehicles, settlers contended with these tiny terrors, doing their best to keep rats and mice out of their houses and barns.

Hard rock miners, however, actually encouraged rats to inhabit the mine tunnels, by saving crusts and crumbs of bread for them. The rats acted as a low-tech safety system. Being ultra-sensitive to tremors or quakes, they provided early warning of impending collapses or cave-ins. If rats suddenly went running for the exit, the mine workers were right behind them.

This may give us a clue that a deterrent that causes vibration or sound waves could be a good choice.

One deterrent that is often reported to be effective, is the use of an electronic rodent repeller such as MouseBlocker.

The low-voltage devices run on your car battery and are easy to install. They emit an ultrasonic frequency heard by rodents, not people. Some of them also activate flashing lights. Another advantage of such products is that you do not have to deal with poisons or messy cleanup of traps.

Tape It Up

One of the newest products addressing the wire-chewing problem is Honda Motor Tape. It is infused with pepper and perhaps some other deterrent and is used to wrap the wire harness. Early reports say it works well. It is not cheap, but it costs much less than replacing an entire electrical system in your vehicle.

Some Less Serious Ways to Discourage Them

So are there other ways that pesky little wire nibblers and insulation grabbers be discouraged? Could a car be disguised with animal pelts, to make it look like a rat-eating predator?

Would a ground squirrel be tricked into thinking your car was a mountain lion or a giant badger with the help of a spectacular paint job? Or perhaps one of those big plastic owls could be stuck under the hood and wired it up with a speaker playing annoying rap music.

Some people park their car over a bucket of mothballs, which is apparently repugnant to rat olfactory receptors.

The family dog or cat may help to keep mouselike pests away, though if the cat gets into an engine, it's bad for everyone—usually worst for the cat.

There are also little buzzer things that are supposed to keep pets off the furniture. They might work.

The problem is not going away, so drivers might be wise to pay a little extra attention next time they notice an unfamiliar squeak in their vehicle.

They are out there.

Some of them know where you park your car.

Anecdotal Results of Dozens of Strategies

Realistically, getting rid of rats may be a lengthy project, requiring multiple strategies. Every situation is different. I have hundreds of anecdotes in over 270 comments sprinkled with suggestions, and you can read them all, or read my article summarizing them.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: The dryer sheets do not work. The rats just made a nest with them in my car. I had eight baby rats to deal with, not to mention chewed up wires. Do you have any other suggestions on how to keep these critters out?

Answer: I suggest that you look through the other suggestions and try two or three of them at the same time. Traps or another deterrent might work.

Question: How often do I have to spray the tires and engine with Pine-Sol?

Answer: If you can't smell it, it is probably time to reapply.

Question: How do mice get into the ventilation system of a car?

Answer: I think a mouse can get in anywhere. The bigger question is how to get them out. It may require a combination of methods.

Question: What if I filled a nylon stocking with mothballs and wrapped it around the tires? Would this help keep rodents away?

Answer: It’s worth a try. It depends on the situation, but I would always recommend using at least two methods.

Question: Would ground Irish Spring soap help deter rodents?

Answer: Some people have reported that it works for them, others have said it doesn't. It may depend upon the kind of rodents you have. I would recommend using two or three methods

Question: Which type of Irish spring soap works best to keep rats out of a car engine and how long will it last before replacing it with a new one?

Answer: Stick with the original scent. If the fragrance is fading, it should probably be replaced.

Question: I found this white cotton like insulation substances and twig like bunches under that inside under top cover of my engine where I check my oil I've only had this 2015 KIA for less than 4 months. At first I thought it came with the car for extra insulation, but then I thought someone hates me and planted it there. Etc. I never thought rodents could've there. I drive at least once a day. What is this?

Answer: It’s hard to identify the culprit without more clues, but it sounds like nesting material. I would get rid of the material and then put some of the suggested deterrents in place before any damage occurs.

Question: Have you heard of the RatMat?

Answer: I had not heard of it, but always glad to hear of a new suggestion. I would encourage people to look it up and to share experiences if you have used it.

Question: Where in a car's engine do you put dryer sheets to keep mice away?

Answer: Most people pin dryer sheets near to the insulation under the hood. Make sure they are not hanging down into the engine. However, this may be one of the less successful strategies, and the sheets need to be replaced often. If possible I would suggest you try one of the electronic devices or traps. It seems that what works for one person may not have any effect for someone else.

Question: What about opening the hood and shining a bright light into the engine all night?

Answer: That seems to work for some. You might want to also employ a secondary method like traps or strong smelling substances like peppermint oil.

© 2008 Rochelle Frank