# cardboad on trucks **URL:** \ **Category:** Factual Questions\ **Created:** [January 28, 2000, 3:52pm UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697 "2000-01-28T15:52:00Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![drollman](https://avatars.discourse-cdn.com/v4/letter/d/f04885/32.png) [@drollman](https://boards.straightdope.com/u/drollman)\ **Post date:** [January 28, 2000, 3:52pm UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/1 "2000-01-28T15:52:00Z")
As the cold snap continues…I’ve seen more and more trucks, van and pick-up’s with a piece of cardboard wired to the grill. (I notice it’s never on a car, always a truck.) What is the purpose od this? Insulation? Does it help the engine warm up quicker? Can a piece of cardboard make THAT much of a difference? I’ve been told an engine only need about 30-60 seconds to be warm enough to drive, regardless of the temp. * * * With God as my witness, I thought turkey’s could fly. ---
**Author:** ![AWB](https://avatars.discourse-cdn.com/v4/letter/a/bb73d2/32.png) [@AWB](https://boards.straightdope.com/u/AWB)\ **Post date:** [January 28, 2000, 4:01pm UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/2 "2000-01-28T16:01:00Z")
WAG: once the truck gets moving, wind chill has the effect of taking heat from the engine. Not enough to affect its performance, but less heat is then available to pump into the cab. So the cardboard’s not to keep the engine warm, it’s to keep the driver warm. * * * When danger reared its ugly head, He bravely turned his tail and fled ---
**Author:** ![DougC](https://avatars.discourse-cdn.com/v4/letter/d/7feea3/32.png) [@DougC](https://boards.straightdope.com/u/DougC)\ **Post date:** [January 28, 2000, 8:48pm UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/3 "2000-01-28T20:48:00Z")
- - - I will ask a truck driver in the morning. I have seen it too, and I heard that it was to keep heat in the engine. I don’t know much about big rigs, but that sounds like a total crock to me. The thermostat controls the engine temperature, no matter what the outside temperature is. I have heard of “summer” and “winter” thermostats, but I don’t know _anybody_ with a passenger vehicle that bothers to change theirs twice a year. Perhaps big diesels are more sensitive to temp, but I can’t imagine it being soooo cold that the engine can’t heat itself (or the cab) up. - MC ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [January 28, 2000, 9:14pm UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/4 "2000-01-28T21:14:00Z")
Covering the grille in cold weather can make a dramatic difference in how quickly a truck warms up to operating temperature. Extreme cold can also make an engine run below optimum temperature so blocking off flow can help. There are even purpose made canvas grille covers for big trucks for those that aren’t so cheap as to use old Post Toasties boxes. ---
**Author:** ![mrblue92](https://avatars.discourse-cdn.com/v4/letter/m/5daacb/32.png) [@mrblue92](https://boards.straightdope.com/u/mrblue92)\ **Post date:** [January 29, 2000, 12:37am UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/5 "2000-01-29T00:37:00Z")
Hmm… Seems to me no one’s really answering the question fully… I’m no mechanic, but consider this: A. Moving engine parts need oil between them, as metal rubbing against metal will wear them out. In fact, most engine wear takes place during cold starts (ie. when the car has been sitting long enough for all the oil to drain into the pan). B. The colder your motor oil is, the more viscous it becomes. The thicker your oil, the more difficult it becomes for the oil pump to do it’s job, and the oil has less of a tendency to flow evenly around parts. At very low temperatures (WAG below -40 F), it can even become thick and sticky, preventing vehicles from running at all. C. Obviously your radiator is designed to “suck” heat away from the engine to cool it. Therefore, to bring the engine (and oil) up to operating temperature faster in cold weather, you block off the radiator. This also has the added benefit of making your heater work considerably faster if it’s a cold start. There is a point, even during cold weather where you should remove the cardboard, lest your vehicle overheat. That’s one reason may people hate the “idiot lights” and insist on real gauges; once your temperature light is on, your already in trouble. ---
**Author:** ![mrblue92](https://avatars.discourse-cdn.com/v4/letter/m/5daacb/32.png) [@mrblue92](https://boards.straightdope.com/u/mrblue92)\ **Post date:** [January 29, 2000, 12:40am UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/6 "2000-01-29T00:40:00Z")
I mean **you’re** already… Or your **car** is already in trouble is more accurate… ---
**Author:** ![mrblue92](https://avatars.discourse-cdn.com/v4/letter/m/5daacb/32.png) [@mrblue92](https://boards.straightdope.com/u/mrblue92)\ **Post date:** [January 29, 2000, 12:46am UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/7 "2000-01-29T00:46:00Z")
Oh, and 30 to 60 seconds to warm-up is probably right if you only ever hit 40 F lows during winter, but here in Michigan it’s a little different. I remember my parent’s old '84 full-size Chevy van (which I think was a 305) sometimes took 10 minutes to warm up if the temp was below or at 0 F. ---
**Author:** ![mouthbreather](https://avatars.discourse-cdn.com/v4/letter/m/a698b9/32.png) [@mouthbreather](https://boards.straightdope.com/u/mouthbreather)\ **Post date:** [January 29, 2000, 12:55am UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/8 "2000-01-29T00:55:00Z")
Please someone, correct me if I am wrong (As if I need to say that…) IIRC from physics class, doesn’t a gas motor’s efficiency **increase** in colder weather? I thought it had something to do with the difference in the temperature between the fuel combustion and the outside air? Something to that effect? Um…someone with a stronger knowledge of physics can take over from here… ::slinks towards the door:: ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [January 29, 2000, 1:06am UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/9 "2000-01-29T01:06:00Z")
In our shop today I noticed a little box of cat radiator repellant. You use it to keep cats from getting near your radiator. Maybe its like that? To keep animals out trying to get warm? * * * “I have gathered a posie of other men’s flowers, and nothing but the thread that binds them is mine own.” ---
**Author:** ![Squee](https://avatars.discourse-cdn.com/v4/letter/s/ba9def/32.png) [@Squee](https://boards.straightdope.com/u/Squee)\ **Post date:** [January 29, 2000, 1:17am UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/10 "2000-01-29T01:17:00Z")
I read a Click and Clack (car fixit guys)article in the newspaper regarding the cardboard over the grill. C&C recommended to a fellow who was having heater core problems. IIRC, the guy having the problems tried replacing the heater core, to no avail… his car was still very cold inside, even with the heater cranked all the way up. I believe they recommended this to keep more heat in the engine, and therefore, keep the engine coolant warmer. Lemme see if I can find their website, or even the original article in the paper… * * * The most rewarding part was when I got my money! -Dr. Nick Riviera ---
**Author:** ![pmh](https://avatars.discourse-cdn.com/v4/letter/p/df705f/32.png) [@pmh](https://boards.straightdope.com/u/pmh)\ **Post date:** [January 29, 2000, 2:55am UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/11 "2000-01-29T02:55:00Z")
> [@](#): > > …doesn’t a gas motor’s efficiency increase in colder weather? … Correct, but for the wrong reason. Increased volumetric efficiency in cold weather is due to increased density of air (assuming that fuel and ignition systems are tuned to take advantage of it). Also only applies after the engine has reached normal operating temperature. Passcar engines are designed to operate in a narrow internal temperature range. Too hot causes internal damage and increased NOx emmissions. Too cold increases internal wear and increases most other emmissions. So, it is important for the motor to reach (and maintain) the proper temperature ASAP. For ambient temperatures outside the design specs of the motor/control system, modifications (like blocking off part of the airflow through the radiator and over the engine) may be benificial. This was very common for vehicles w/ large multi-row radiators and little or no electronics (back in the good ol days). But I don’t think that’s the case here. The electronics of any passenger vehicle manufactured in the last ten years should be capable of adapting to operation at ambient temperatures in the -20, +120 range w/o any problem. I think AWB nailed it. Wussy drivers. ---
**Author:** ![DougC](https://avatars.discourse-cdn.com/v4/letter/d/7feea3/32.png) [@DougC](https://boards.straightdope.com/u/DougC)\ **Post date:** [January 29, 2000, 3:04am UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/12 "2000-01-29T03:04:00Z")
- - - The water in the radiator is controlled by the thermostat; if the engine is cold, water doesn’t circulate. The engine has to heat up enough that the thermostat opens to allow water to cool the engine. This is the way it works, no matter what the outside temperature is. - I.E., When the engine is “cold”, the radiator water isn’t circulating anyway. If you think a car or truck engine desn’t get hot during the winter, drive for thirty minutes or so, stop, pop open the hood and put your hand on the engine block. - MC ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [January 29, 2000, 3:10am UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/13 "2000-01-29T03:10:00Z")
The Car Talk (Click & Clack) column mentioned above is at [http://cartalk.cars.com/Columns/CC/CC7591TXT.html](http://cartalk.cars.com/Columns/CC/CC7591TXT.html) - they make it clear that it is a hack and not a real solution. ---
**Author:** ![mrblue92](https://avatars.discourse-cdn.com/v4/letter/m/5daacb/32.png) [@mrblue92](https://boards.straightdope.com/u/mrblue92)\ **Post date:** [January 29, 2000, 4:52am UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/14 "2000-01-29T04:52:00Z")
pmh: Are you referring strictly to passenger cars/trucks, or does that include large diesels? They are typically the vehicles I see with “radiator shields” (or whatever term you’d prefer). I’m also a little curious if you’ve ever driven a large passenger vehicle in sub-zero weather with a poor heater 🙂 ---
**Author:** ![pmh](https://avatars.discourse-cdn.com/v4/letter/p/df705f/32.png) [@pmh](https://boards.straightdope.com/u/pmh)\ **Post date:** [January 29, 2000, 6:06am UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/15 "2000-01-29T06:06:00Z")
MC: I was referring to ambient temps that are _so_ cold that the normal thermostat cannot keep enough heat in the engine (FTR, some ammount of coolant flows through the thermostat/bypass @ any temp.) mrblue92: I was referring to vehicle design limits. Large or special purpose vehicles have special operating procedures that (so long as followed) are within those limits (i.e. semi “air dams”). My point was: cardboard over the rad _used_ to be an acceptable “band-aid” fix. Now, it would have to be _very_ cold for it to be neccesary. > [@](#): > > ever driven a large passenger vehicle in sub-zero weather with a poor heater? How about a '73 fullsize Dodge van @-20F? I can recover from frostbite, but I’d never be able to find internals for the 360. ---
**Author:** ![mrblue92](https://avatars.discourse-cdn.com/v4/letter/m/5daacb/32.png) [@mrblue92](https://boards.straightdope.com/u/mrblue92)\ **Post date:** [January 29, 2000, 7:16am UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/16 "2000-01-29T07:16:00Z")
pmh: Ah I see, I missed the “last ten years” part. So would you say, theoretically, that cardboard in a 70’s or 80’s truck/van is not necessarily the sign of a “wussy” driver? (Just for clarification, mind you; my truck’s a '99 and cardboard-free.) ---
**Author:** ![pmh](https://avatars.discourse-cdn.com/v4/letter/p/df705f/32.png) [@pmh](https://boards.straightdope.com/u/pmh)\ **Post date:** [January 29, 2000, 9:26am UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/17 "2000-01-29T09:26:00Z")
mrblue92: If said truck/van lacked modern engine controls (ambient temp or air density sensor, EFI, O2 sensor, etc), then yes, I would agree. If the vehicle has a “tow package” (larger rad), it may even be a good idea (just keep an eye on the gauge). ---
**Author:** ![sly](https://avatars.discourse-cdn.com/v4/letter/s/e56c9b/32.png) [@sly](https://boards.straightdope.com/u/sly)\ **Post date:** [January 29, 2000, 5:46pm UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/18 "2000-01-29T17:46:00Z")
The only vehicles I have noticed with the cardboard are those with diesel engines. Diesel engines operate quite differently than gasoline engines. Diesels rely on the heat of compressed air to ignite their fuel. When it’s cold (and, believe me, it’s cold), compression alone may not produce enough heat for the fuel to burn. Diesel fuel will only burn under intense heat and pressure. Glow plugs are used to heat the air (before starting) to the required tempurature which is why, when starting a diesel equipped vehicle, you turn the ignition “on” for a few seconds before actually starting the engine. This gives the glow plugs a chance to heat the air. In frigid cold, a block heater is used to make cold starts possible. Anyway, I’ve always assumed that these chaps don’t have block heaters or that they aren’t functioning properly. ---
**Author:** ![mrblue92](https://avatars.discourse-cdn.com/v4/letter/m/5daacb/32.png) [@mrblue92](https://boards.straightdope.com/u/mrblue92)\ **Post date:** [January 29, 2000, 5:48pm UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/19 "2000-01-29T17:48:00Z")
Thanks, pmh. Are you an engineer or a mechanic? handy: I’m a little curious about the “cat repellant”… Anybody know if it’s supposed to go in the radiator (ie. in your coolant) or on top of the radiator? In the former case, I’d say it’s purpose was keep cats from drinking the antifreeze, but that wouldn’t be a problem if your car didn’t leak. More likely its the latter, as my father grew up on a farm and had cats killed that way. They’d crawl up in the engine compartment because it was nice and warm, but when somebody started the car, they’d get scared and jump through the fan or get caught in the belts. Ick. ---
**Author:** ![pmh](https://avatars.discourse-cdn.com/v4/letter/p/df705f/32.png) [@pmh](https://boards.straightdope.com/u/pmh)\ **Post date:** [January 30, 2000, 4:09am UTC](https://boards.straightdope.com/t/cardboad-on-trucks/6697/20 "2000-01-30T04:09:00Z")
mr blue92, I’m an EE working as a mechanic, so a little of both. sly, D’oh! I didn’t even consider that aspect. You are, of course, correct. [Next page](https://boards.straightdope.com/t/cardboad-on-trucks/6697.md?page=2)