Trunk Temperatures II: The Cooler Strikes Back

My first experiment (link) showed that a cooler moderates the temperature swings more than it actually keeps things cool (without something cold inside).

But that left me wondering how much difference freezing the bottles first would produce. Here's the result:


The lows are from the night before each high. By Wednesday we were back up to the previous temperatures.

The good news is that the ice did last for about 24 hours, even in a trunk with the sun beating on a glass hatchback.

In my experience your pretty accurate when you say the cooler moderates temperature changes but doesn't do much to keep things cooler. Makes sense. Insulation just slows heat transfer.

You can further slow temperature fluctuation by adding insulation and thermal mass. I like a kind of reflectorized, like space blanket, bubble wrap to add insulation. I make pouches out of it and then place the pouch in a cooler.

The easiest way to add thermal mass is to stuff a couple of bottles inside the insulation. Most kits benefit from a few liters of water. You can limit the top end somewhat by finding cooler places to keep the kit. In my truck the coolest spot is on the floorboard. If you use the floorboard find out where the catalytic converter is and avoid placing your kit near that spot. Catalytic converters can get very hot.

re: Hot Catalytic Converters

Years ago M'Lady and I went to Swap Meets regularly. One of them had a dirt parking lot, with weeds around the edges.

Every single time we went to that one, sometime during the few hours we were there, there'd be a "Would the owner of the [such-and-such] car with license [thus-and-so] please return to your car. It is on fire." over the PA. Every. Single. Time.

The one time I had to park on the edge, I found a place where they were already bent down, and then got under the car with the tire iron and scraped down to bare dirt for a good foot around the converter. And I STILL worried about it the entire time we were there.


Trunk Temps:

I've got at least one more experiment in mind, then I'm just going to start parking in the front, where there's shade. I'll have to walk around back to get in in the mornings -- I don't rate a key -- but sometimes you just have to make sacrifices . . . .

Are you planning on storing something in your ice chest in your trunk for long periods of time or is this just a for-fun test??

Both, actually.

The cooler holds four .7 liter bottles very nicely, and they are part of my general preparedness plan. I want to find out what they go through, and how often I need to change them out.

There are also 2 1L bottles in my GHB in the trunk, plus a couple of food bars. This will tell me what those are going through, too.

I also just enjoy doing this sort of thing. The classes with labs were always my favorites.

Gotcha.

I would imagine that the inside of an ice chest will equal the trunk temperature after a matter of days (no ice), and then once it does it will take even longer to cool the inside of the ice chest back down at night.

That's my guess at least... your data seems to point toward that?

My guess is that the inside of the cooler will fluctuate around a temp midway between the high and low of the trunk.

Check this link to see the first set of readings, a full week's worth that confirms exactly what Russ said.

I think if you kept doing it more days what I said would be true..

Look at the cool temps of the ice chest.. they are going up while the trunk 'cool' temps are staying about the same. Eventually the inside of the ice chest will be the same as the trunk, and then it will take longer to cool off than the trunk like your test also shows thus things in the ice chest left in there for the duration of a summer will have been kept warmer longer than if left in the trunk alone.. I didn't do the math on this but it looks like it would happen If you want to compute it go for it and let us know

It was almost break-even after the last day in the trunk with lows and highs 97/95. Meaning it almost stayed the same temp in the ice chest the entire day... at this point the ice chest seems to be working against itself. I would imagine the high is going to go up and so will the low too as the ice chest retains the higher temps during the night too.

Obviously if you are switching out your water weekly then this data is useful but if yow ant to see if you can leave it in there a month or more then you need to do longer tests.

Also, the data should not be called TRUNK since you have a hatch and not a real trunk. Real trunks are sealed a wee bit better than a hatch. (Just pointing this out for others who may read. ALong with all car trunk temps will be different and so will results with different brands of ice chests.)

I like the testing!
Keep it up

Thanks, Todd.

Right now I'm trying a couple different ideas to see what (if any) difference they make.

Frozen bottles bought a day or so of leeway, even in direct sun all day. I'll remember that for the next time I take a trip.

Next week I'll be doing this with a leftover silverized sun shield laid on top of the hatch deck, to see how that affects the trunk temperature.

I'll be pulling out one of the bottles every couple of weeks to see how long it takes them to start tasting 'funky'. And checking periodically to see how the Clif Bars in my GHB are faring.