Rats in the Engine Bay: A Valley, Foothill and Cabin Problem

The first sign is usually a warning light, a dead start or a strange smell through the vents. The cause turns out to be a nest on top of the engine and a wiring harness that has been chewed through in a few places. In farm country, foothill towns and anywhere cars sit for weeks at a time, this is a common enough repair that mechanics recognize it at a glance.

Why parked cars attract them

An engine bay offers exactly what a rodent wants: shelter, warmth after the car has been driven, and quiet. Cars that sit are the most exposed, such as the second car, the truck kept at the cabin, or the vehicle stored over the winter. In agricultural areas, people commonly notice more activity when fields are worked or harvested and animals move. You will also hear that some wire insulation contains plant-based material that attracts chewing; whether that makes a real difference is debated, but rodents gnaw on plenty of things regardless.

Signs you have a tenant

• Leaves, grass, insulation or shredded paper packed on top of the engine or around the battery.
• Droppings, or acorns and seeds stashed in the air filter box.
• Chewed hoses, wiring covers or the hood insulation pad.
• A musty or rotten smell when the fan runs, or a cabin air filter full of debris.
• New warning lights or electrical faults that come and go.

Prevention that actually helps

Nothing is foolproof, but the habits that work are simple.

1. Drive the car regularly, even briefly. A car that moves often is a poor nest site.
2. Remove the attraction. Pet food, bird seed, fallen fruit and open trash near where you park bring rodents in.
3. Clear clutter such as woodpiles, boxes and brush away from the parking spot.
4. Use traps around the area, not poison near the car. A poisoned rodent can die inside the engine bay or ducting, which brings a new set of problems.
5. Look under the hood every week or two on a car that is stored.
6. Garage it if you can, and seal the obvious gaps.

Some owners also use deterrent tapes, sprays or under-hood lights. Results are mixed, so treat them as extras, not a substitute for the basics.

What insurance does with chewed wiring

Damage from animals is commonly submitted under comprehensive, the part of a policy that covers losses other than collisions. But this is an area where policy wording really matters. Some policies exclude damage by vermin or insects, and many exclude wear and tear or damage that happened gradually. How a rodent claim is treated varies by insurance company, so read the comprehensive section and its exclusions on your own policy. Compare the repair estimate with your deductible, too, since small repairs may not be worth a claim.

If you do claim, get the mechanic to write the diagnosis down, including that the damage was caused by rodents, and keep photos of the nest and chewed parts. Manufacturer warranties and service contracts commonly exclude animal damage, so check yours before assuming it is covered there.

Storing a car for a season

If you are putting a car away, think about insurance and registration together. A car that stays registered needs insurance on record with the DMV, and the DMV suspends the registration of a registered vehicle with no insurance reported. If the car will not be driven, towed, stored or parked on public roads for the whole registration year, the DMV's planned non-operation status may fit instead. Either way, keeping comprehensive on a stored car protects it from exactly this kind of damage, as well as theft and fire.

If you are not sure what your policy says about animal damage or a stored car, you can have it checked in a couple of minutes.