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.
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
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.
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.
I mean you’re already…
Or your car is already in trouble is more accurate…
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.
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::
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.”
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…
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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.
The Car Talk (Click & Clack) column mentioned above is at http://cartalk.cars.com/Columns/CC/CC7591TXT.html - they make it clear that it is a hack and not a real solution.
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 
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.
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.
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.)
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).
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.
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.
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.