Rats in the Garage and Car Engine: Signs and Fixes

Signs of rodents in the garage

• Droppings along the walls, behind storage and on shelves
• Chewed bags of pet food, birdseed or grass seed
• Shredded cardboard, paper or fabric used for nests
• Gnaw marks on boxes, plastic bins and wood
• Rub marks along the base of walls and on the garage door track
• Droppings or nesting on top of the water heater or behind the fridge

Rice-sized droppings point to mice. Droppings roughly half an inch or longer point to rats. See rat droppings identification.

Signs of rodents in a car

Pop the hood and look with a flashlight. Common signs:

• Nesting material such as leaves, insulation, paper or shredded hood liner on top of the engine or near the battery
• Droppings on the engine cover, air filter box or in the cabin air filter
• Chewed wiring, hoses or foam
• Acorns, seeds or pet food stashed in the air filter housing
• A musty smell from the vents when the fan runs

Warning lights or a car that will not start after sitting can mean chewed wires. Cars, RVs and boats that sit for days or weeks are most at risk. Rodent damage to wiring can be costly, so check any car that sits often.

Seal the garage

Most San Diego garages have the same weak spots:

• The roll-up door's bottom seal, which dries and curls in the sun
• The side corners where the door meets the jamb
• The side door, with no sweep or a worn one
• Gaps around the water heater vent, gas and water lines and the electrical panel
• The dryer vent if it exits through the garage wall
• Gaps at the slab edge in older detached garages

Replace the bottom seal, add brush or rubber seals at the side corners, and put a sweep on the side door. Fixr lists a professionally installed steel door sweep at $60 to $125. Pack gaps around pipes with steel or copper mesh and finish with sealant. The county says to seal openings wider than a quarter for rats, and its hantavirus brochure says dime-sized or larger for mice.

Take away food and cover

• Move pet food, birdseed, chicken feed and grass seed into metal or hard plastic bins with tight lids
• Replace cardboard boxes with plastic bins and put them on shelves, not the floor
• Leave a gap between storage and the walls so you can see droppings and set traps
• Keep the garage door closed at night
• Clean under and behind a garage fridge or freezer
• Store firewood outside on a rack, as the county advises: 18 inches off the ground and 12 inches from walls

Trap along the walls

Rodents in a garage run along walls and behind stored items. Set snap traps against the walls with the trigger end toward the wall, near droppings and behind storage. For rats, use rat-sized traps on shelves and in the rafters. Covered trap boxes keep pets and kids away from the trigger. Avoid bait in a garage where a poisoned rodent might crawl into a car or a wall to die. Most anticoagulant baits are also prohibited for home use in California under AB 1788 and AB 2552. See best rat and mouse traps.

Protect the car

• Use cars that sit more often, or at least open the hood and check them weekly
• Do not store food, pet food or trash in the car or under the car cover
• Clean nesting material out of the engine bay with gloves on
• Check and replace the cabin air filter if you find droppings or nesting in it
• Park away from fences, ivy and stored items when you park outside

If you find chewed wiring, have a mechanic check it before you use the car.

Clean up safely

Open the garage door for 30 minutes before cleaning, wear gloves, spray droppings and nests with a bleach solution of 1 part bleach to 9 parts water, let it soak 5 minutes, and wipe up with paper towels. Do not sweep or use a leaf blower. In homes near open space where deer mice may nest, the county's hantavirus brochure suggests airing out for at least 2 hours and soaking 15 minutes. See garage rodent control.