A car with the engine off is an uninsulated metal box with large windows, and it loses heat faster than a house. The trap is that it works both ways: on a bright, cold afternoon a car parked in direct sun still heats up behind glass. If the errand is not for your pet, leave them at home.
Why the winter version gets ignored
The summer message has landed. Most people would not leave a dog in a car in July, and most would say something if they saw one. The winter equivalent has no such reflex, partly because the danger is slower and partly because it feels counterintuitive to worry about an animal in a coat.
But the physics are not sympathetic. Glass and thin sheet metal are poor insulators and there is no heat source once the engine is off. A cabin that was comfortable when you parked follows the outside temperature within a short time, and on a clear night the glass and metal radiate heat away to the sky and can drop several degrees below the air temperature, which is why you scrape frost off a car on a morning the thermometer says is above freezing. With no heat source inside, the cabin simply follows the outside temperature down.
In the Tri-Cities that usually means a damp, raw cold rather than a deep freeze, which is its own problem: damp cold pulls heat out of an animal considerably faster than dry cold at the same reading.
Who has the least margin
A healthy, thickly coated adult dog sitting in a car for ten minutes on a mild December afternoon is fine. The animals who are not fine, and who are the reason this article exists:
- Puppies and kittens, who cannot hold their temperature and have almost no reserve
- Older pets, particularly arthritic ones, who stiffen in the cold and cannot move to generate heat
- Thin, short-coated and single-coated animals, and hairless breeds
- Small dogs and cats, where the ratio of surface area to body mass is against them
- Anyone unwell, underweight, or recovering from illness
- Any animal who has been sedated or has had a procedure that day. Sedation interferes with temperature regulation directly, so a pet going home from an appointment needs a car that is already warm, not one that will warm up on the way
The signs, and the one that matters most
Shivering is the body working, and it is a reasonable early warning. The important sign is the one that looks like improvement.
- Shivering, hunching, tucking the tail, lifting paws
- Whining, restlessness, scratching at a door
- Cold ears, paws and tail tip to the touch
- Shivering that stops while the animal is still cold. This is not recovery. It means the body has given up trying, and it is the point at which this becomes urgent
- Stiffness, slowing, reluctance or inability to stand
- Pale or greyish gums
- Limp, unresponsive, hard to rouse
If you reach the last three: get them somewhere warm, wrap them in blankets, warm them gradually with body heat rather than with direct heat, and phone us on the way in. If there is no veterinarian on duty or we are closed, go to an open emergency veterinary hospital instead. Do not use a hot bath or put a hot water bottle against the skin, because warming a cold animal too quickly causes its own problems.
The mistake that makes it worse: leaving the engine running
This feels like the obvious solution and it introduces three new problems.
Carbon monoxide. If snow, slush or debris blocks the tailpipe, exhaust gas backs up and can enter the cabin. Carbon monoxide is colourless and has no smell, and it is worth correcting a common misconception here: it is very slightly lighter than air and mixes evenly through a space rather than pooling near the floor, so there is no safer part of the car. Pets are often affected before people would be, because a smaller body with a faster breathing rate takes the gas up more quickly. The signs are vague on purpose: sleepiness, wobbliness, vomiting, confusion, an animal who will not get up. If that happens with an engine running, turn it off, get everyone out into fresh air, and come in, or go to an open emergency veterinary hospital if we are closed. Oxygen is the first thing needed, so phone ahead.
The vehicle itself. A running car with the keys in it is a theft risk, and dogs do knock gear selectors and window switches. A dog who can open a window in a running car is a dog who can leave.
It does not solve the problem it is meant to. Climate control cycles, the sun moves, and the car is still unattended.
The other direction, which surprises people
A cold day does not protect against an overheated car. Sunlight through glass heats the interior regardless of the air temperature outside, and a car parked in full sun on a crisp, clear February afternoon can become uncomfortably warm inside while the outside reads a few degrees above freezing. Add a dog in a winter coat who cannot take it off and you have a genuine problem.
So the shade-versus-sun calculation does not reverse in winter, it just gets more complicated. The reliable rule is the one that avoids the calculation altogether.
What to do instead
- If the trip is not for your pet, leave your pet at home. This is the whole article in one sentence, and it removes every judgement call below it.
- Plan the route so stops happen with someone in the car, or so your pet is dropped home first.
- Warm the car before loading an older, sedated or unwell animal, rather than relying on the drive to do it.
- Blankets in the car, not just on the bed. A folded blanket between a pet and a cold metal floor makes a real difference, and the floor is the coldest surface in the vehicle.
- Insulate the carrier. A hard carrier on a cold floor with a thin mat is a cold place; a blanket underneath and a cover over part of the top changes it.
- Check the water has not frozen if you travel with a bowl.
- Knock on the hood before you start the engine in cold weather, and check the tires. If you find a cat in the engine bay or a wheel well and it will not come out, do not reach in: call the BC SPCA or local animal control to have it removed safely. Cats sleep against warm engine blocks and on top of tires, and that is a winter-specific habit with a terrible outcome.
- Clear snow from the tailpipe before running the engine at all, whether or not an animal is on board.
- Keep washer fluid, coolant and ice melt out of the cabin and the trunk where a pet travels, or at least sealed and upright. If your pet licks or drinks any of these, phone us or an open emergency veterinary hospital immediately and say what it was, because coolant in particular is time-critical and a very small amount matters.
If you find an animal in a cold car
Note the time, the location and the plate, and look at the animal rather than at the thermometer: an animal who is shivering hard, crying, or who has gone quiet and still is in a different category from one who is asleep and relaxed. If the car is on private property such as a store lot, staff can often page the owner quickly. If the animal looks to be in distress, call the BC SPCA or local authorities rather than taking action yourself, and stay with the car until someone arrives. Do not break a window; that decision belongs to someone with the authority to make it.
Come in through our urgent care for an animal who has become cold and gone quiet, who stopped shivering while still cold, or who is unsteady after sitting in a vehicle with the engine running. Our diagnostics team is what a possible exhaust exposure or an unexplained collapse needs, and our medical services team manages the warming and monitoring, which usually takes longer than owners expect because the recovery is deliberately gradual.
We are open 8:00 AM to 8:00 PM Monday to Friday with a veterinarian on duty 10:00 AM to 6:00 PM, and 9:00 AM to 6:00 PM on Saturday with a veterinarian on duty 10:00 AM to 5:00 PM. On Sunday we are open 10:00 AM to 4:00 PM for retail and bookings only, with no veterinarian on duty, and we are closed on statutory holidays. Sunday is also the day people run errands with the dog in the car, so if your pet has become cold and limp, has stopped shivering while still cold, or is wobbly and sleepy after an engine has been running, go straight to an open emergency veterinary hospital rather than to us, and phone ahead before you leave. The same applies outside our veterinarian hours on any other day. This is not something to hold overnight.
Our guide to caring for your senior dog or cat covers the twice-yearly visits, joint support and bedding changes that older pets need, and they are among the animals with the least margin in a cold car.
Questions we are asked
How cold is too cold to leave a dog in the car for ten minutes?
There is no single number, which is an unsatisfying answer, so here is a more useful one: the variables that matter are your dog’s size, coat, age and health, whether the car is in sun or shade, whether it is damp, and how long “ten minutes” actually turns out to be. Because every one of those is uncertain, the reliable rule is not to do it. If you are weighing it up, that in itself is a sign the margin is thinner than you would like.
Is it really dangerous to leave the engine running for warmth?
It introduces risks rather than removing them. The serious one is exhaust gas entering the cabin if snow or slush blocks the tailpipe, and your pet would be affected before a person would notice anything. There is also the theft risk and the fact that dogs operate switches. If the only way the arrangement works is with the engine running, the arrangement does not work.
My cat travels in a carrier. Does this apply?
Yes, and in some ways more so. Cats are small, they are usually in a hard plastic carrier sitting on a cold floor, and they do not move around to generate heat the way a loose dog does. Put a blanket under the carrier rather than only inside it, cover part of the top so there is somewhere sheltered, keep it off the floor if you can secure it on a seat, and never leave it in an unattended car in cold weather.
Can a car really overheat in winter?
Yes, in direct sun. The interior heats from sunlight through glass, and that process does not care much what the outside air temperature is. A car parked in full sun on a clear, cold day gets noticeably warm inside, and a dog in a winter coat has no way to shed it. This is why “it is cold out” is not the safety margin people assume, and why shade matters year-round.
We are collecting our dog after a procedure. Anything specific?
Yes, and thank you for asking, because this is the situation with the least margin of all. Sedation interferes with the ability to hold body temperature, so warm the car up before you arrive rather than relying on the journey. Bring a blanket, keep the cabin warm rather than merely not cold, go straight home, and do not leave your dog in the car for any errand on the way. We will tell you what to watch for that evening.
Why knock on the hood?
Because cats sleep against a warm engine block and on top of tires in cold weather, and the outcome when the engine starts is catastrophic. A knock on the hood and a quick look at the wheels takes five seconds. It is worth doing every cold morning whether or not you have a cat, since the cat in question is usually someone else’s or nobody’s.
What if I see a dog in a cold car and the owner is not around?
Note the time, the plate and the location, and assess the dog rather than the weather: shivering hard, crying, or gone still and quiet are the signs that matter. Ask store staff to page the owner, which often works within minutes. If the dog appears to be in distress, call the BC SPCA or local authorities and wait with the vehicle. Do not break a window yourself.
Speak to the team at Tricity Animal Hospital
If your pet has become cold and quiet, stopped shivering while still cold, or is unsteady after time in a vehicle with the engine running, phone us and come in. Outside our hours, go to the nearest open emergency veterinary hospital and phone ahead before you leave.
Published by the team at Tricity Animal Hospital.
This article is educational in nature and is not a replacement for hands-on assessment of your own pet by a veterinarian.
Tricity Animal Hospital
26-2755 Lougheed Hwy, Port Coquitlam, BC V3B 5Y9
Phone: (604) 942-2225
Email: info@tricityvet.ca
Hours: Monday to Friday 8:00 AM to 8:00 PM (veterinarian on duty 10:00 AM to 6:00 PM); Saturday 9:00 AM to 6:00 PM (veterinarian on duty 10:00 AM to 5:00 PM); Sunday 10:00 AM to 4:00 PM, retail and bookings only with no veterinarian on duty; closed statutory holidays