【Real Record】Can you use a hot water bottle during this season!? Challenging below-zero car camping without an FF heater

When it comes to heating equipment for car camping, the standard is the "FF heater," which warms up the interior using the car's fuel and other resources. However, my Jimny is not equipped with one, so I spent the frigid night with traditional winter camping gear and an analog hot water bottle. Can a hot water bottle be used during this below-freezing season?

Cold wave approaching! The temperature is forecasted to be below freezing... trying car camping

On this day of car camping, the outside temperature is around 5℃ even during the day. And at night, it is forecasted to drop below 0℃. However, during the day, the sunlight is warm, making for a very pleasant climate. Just the cold wind is strong, and it can be expected to get quite cold when the sun sets and the sunlight disappears.

I was spending time inside the car while sitting in the “mame-tan” kotatsu I wrote about in a previous article, but the cold wind was so strong that I had to keep the back door closed, making it painful to go outside to set up my sleeping area.

自作の「豆炭キャンプこたつ」で車中泊！愛車のジムニーにセットして使い心地をチェック

以前作った「キャンプこたつ」の本来の目的は、ジムニー車内に設置して車中泊すること。今回は実際に湖畔のキャンプ場で車中泊し、使い勝手をテストしてきました。新たに発見できたポイントについてレポートしていきます！

I laid out the air mattress and sleeping bag, and started boiling water with a gas burner to prepare for sleep.

On a night of severe cold, boiling water for a hot water bottle along with instant ramen.

Here the hot water bottle makes its appearance. The author's Jimny does not have an FF heater, and since it cannot run the car's heater all night at the campsite, hot water is poured into the hot water bottle to prepare for bed. After having some instant ramen for a midnight snack, the kotatsu is tidied up and I get into the sleeping bag.

I prepared two simple thermometers to measure the temperature, and found that the outside temperature was 0℃, while inside the car it was 9℃. Due to boiling water and such, the inside of the car was somewhat warm. However, as time passes, it is clear that the inside of the Jimny, with its low airtightness, will drop to the same temperature as outside, and cold air is expected to reach even inside the sleeping bag.

Can a hot water bottle help survive a winter in the car?

It's time for bed. I take off my jacket and down pants, and get into the sleeping bag. The hot water bottle keeps my often cold toes warm, which is surprisingly comfortable. At this point, I don't feel cold and am in a cozy and comfortable state. I was able to fall asleep right after turning off the lights.

Supercooled tea turns into a slushy! Waking up in a frozen car.

This is the scene inside the car in the morning. The panel on the ceiling has frozen, warping due to the temperature difference.

Regarding the sleeping comfort using a hot water bottle, the low temperature in the early morning allowed cold air to penetrate the sleeping bag, resulting in little effect, and I woke up early. Even with a hot water bottle, if the winter mat and sleeping bag are too light, you will feel cold. Until now, I have been getting into my sleeping bag without taking off my jacket and down pants during winter camping, but similar gear is necessary for sleeping in the car as well.

When I tried to heat the tea that had been left in the drink holder and poured it into the kettle, it unexpectedly turned into a slushy state. This phenomenon seems to be called "supercooling," which occurs with cooled liquids that did not form the nuclei necessary for ice. It crystallizes when a shock is applied to a liquid that has been cooled slowly and uniformly to around -5°C. The occurrence of supercooling indicates that the inside of the car had been close to -5°C for an extended period.

By the way, supercooling can also occur with rain droplets in the upper atmosphere, resulting in a phenomenon called "freezing rain," which freezes everything on the ground and trees, and is said to happen frequently in North America.

Next time, I must be fully prepared with a hot water bottle and extra clothing for car camping.

Given the current situation, I definitely do not want to do any more car camping, so on the way back, I headed to Montbell and purchased winter version underwear, "Geoline," which I am currently wearing. Until now, I have worn mid-thickness top and bottom, but I've decided to switch to a thick top and use down pants that are easy to put on and take off for the bottom. Uniqlo's ultra-light down seems good too, but considering using it as sleepwear, I opted for strengthening the underwear.

Winter outdoor activities can be challenging, as I often find points of dissatisfaction and areas for improvement, but it is the perfect season to test gear performance. With a spirit of trial and error, I plan to keep enjoying winter car camping.

Reporting and text by Kazuma Tanaka.

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