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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / November 2005A question about heater
If I just move the slider to maximum heat, but keep the fan OFF, does it consume any gas? My 94' Caravan's heater works great, in early winter I don't need to turn on the fan. It gives out lot of hot air though. I guess it uses recycled heat from under the hood, right? However, I noticed a significant drop (>15%) on gas mileage each year when temperature comes down to around freezing point. It's normal? or anything else I can check on? Thanks. >If I just move the slider to maximum heat, but keep the fan OFF, does it >consume any gas? Nothing you do with the controls will consume enough energy to make any difference in your gas mileage. Perhaps in a year, the fan might use up a couple of bucks worth of gas. >My 94' Caravan's heater works great, in early winter I don't need to turn on >the fan. It gives out lot of hot air though. I guess it uses recycled heat >from under the hood, right? It uses heat from the cooling water. If it didn't use the heat, the heat would be dumped in the radiator. It's free. >However, I noticed a significant drop (>15%) on gas mileage each year when >temperature comes down to around freezing point. It's normal? or anything >else I can check on? That's not unusual depending on how short your trips are. It takes some energy to warm up the engine for normal operation and it works less efficiently in the process. Make sure you have good spark plugs, air filter, and fuel filter. Change all your fluids if you haven't recently (engine oil, engine coolant, tranny oil) Check the condition of your ignition wires and distributor cap and rotor. If your 'check engine' light ever comes on, have its codes read out. Good Info! "Nothing you do with the controls will consume enough energy to make any difference in your gas mileage." Even with Defrost and Fan on? Actually I don't mind a few more bucks on gas. Just try to avoid more load on the engine of my own car (as minimizing use of AC in summer). I'll try start with spark plugs and air filter myself. Thanks. >>If I just move the slider to maximum heat, but keep the fan OFF, does it >>consume any gas? [quoted text clipped - 28 lines] > rotor. If your 'check engine' light ever comes on, have its codes read > out. >Good Info! >"Nothing you do with the controls will consume enough energy to make any >difference in your gas mileage." >Even with Defrost and Fan on? Actually I don't mind a few more bucks on gas. Yes. Defrost doesn't use any power -- it's just a vent setting. The heat is free. >Just try to avoid more load on the engine of my own car (as minimizing use >of AC in summer). The fan's power consumption is negligable. Don't worry about it. It isn't even 20th the power consumption of the AC Stop at a traffic light and you'll have used more gas than required by the fan for the entire trip. >I'll try start with spark plugs and air filter myself. Thanks. > >Good Info! > [quoted text clipped - 4 lines] > Yes. Defrost doesn't use any power -- it's just a vent setting. The heat > is free. On many if not most cars defrost runs the AC compressor. Ted Yeah. Ever read newer car's manuals. Mentioned that AC will run at Defrost. Does it put the same load on engine as cooling in summer? Why it needs AC? It can simply blow hot air to the front vent under windshield. >> >Good Info! >> [quoted text clipped - 10 lines] > > Ted When the AC is on, it is on. It is in theory safer to have the windshield defrost faster so having the AC on to dry out the air helps do that. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Aug./05 http://www.imagestation.com/album/index.html?id=2120343242 (More Off Road album links at bottom of the view page) > Yeah. Ever read newer car's manuals. Mentioned that AC will run at Defrost. > Does it put the same load on engine as cooling in summer? [quoted text clipped - 16 lines] > > > > Ted >When the AC is on, it is on. It is in theory safer to have the... It isn't on 100% of the time. > >When the AC is on, it is on. It is in theory safer to have the... > > It isn't on 100% of the time. LOL! Then it would be off wouldn't it.... Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Aug./05 http://www.imagestation.com/album/index.html?id=2120343242 (More Off Road album links at bottom of the view page) >> >When the AC is on, it is on. It is in theory safer to have the... >> [quoted text clipped - 3 lines] > > Then it would be off wouldn't it.... Doesn't it cycle on-and-off? Can't imagine the compressor running continuously. > >> >When the AC is on, it is on. It is in theory safer to have the... > >> [quoted text clipped - 6 lines] > Doesn't it cycle on-and-off? > Can't imagine the compressor running continuously. It likely cycles the pump just like if you have it turned 'on', which is what the defrost setting does. Turn it 'on' that is. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Aug./05 http://www.imagestation.com/album/index.html?id=2120343242 (More Off Road album links at bottom of the view page) > Doesn't it cycle on-and-off? Can't imagine the compressor running > continuously. You have no experience with EPR/STV or variable-displacement compressor setups, then. >> >When the AC is on, it is on. It is in theory safer to have the... >> >> It isn't on 100% of the time. >LOL! Nice gufaw! >Then it would be off wouldn't it.... NO you idiot. It is on a percentage of the time. On 30 seconds, off 4 minutes, on another 30 seconds, off 2 minutes, on 30 seconds, off 3 minutes, for example. Can you understand the concept? >> When the AC is on, it is on. > NO you idiot. It is on a percentage of the time. On 30 seconds, off 4 > minutes, on another 30 seconds, off 2 minutes, on 30 seconds, off 3 > minutes, for example. That is true in cycling-clutch systems. A lot of vehicles do NOT use cycling-clutch systems. Instead, they use variable-displacement compressors, or STV/EPR valves with fixed-displacement compressors. These systems run the compressor full time, 100% of the time, when an A/C or defog mode is selected. You, living in Arizona, can be forgiven for being ignorant of the workings of such things as defoggers. > >> >When the AC is on, it is on. It is in theory safer to have the... > >> [quoted text clipped - 8 lines] > on another 30 seconds, off 2 minutes, on 30 seconds, off 3 minutes, > for example. Can you understand the concept? But, but, isn't that how it acts when it is on? Mike > When the AC is on, it is on. If you indend that as a response to his question, "Does it put the same load on engine as cooling in summer?" then I have to disagree. The actual load the A/C puts on the engine depends on the ambient temperature VERY strongly. When the ambient temp is high, the air being drawn over the evaporator and blown into the car boils the refrigerant much faster and loads it with more heat energy before it is returned to the compressor. That in turn greatly increases the high-side pressure and tempreature, and thus the load on the compressor. In addition, hot air being the only thing available to cool the evaporator in summer FURTHER increases the high-side pressure and FURTHER increases the load on the compressor in the summer. And on top of THAT, since the A/C is themostatically controlled to prevent the evaporator temperature from ever falling below freezing or rising above roughly 40 degrees F when the AC is "on," it will spend a much greater percentage of the time actually running in the summer than in the winter. This seems exactly answered my last question... THANKS ALL. >> When the AC is on, it is on. > [quoted text clipped - 14 lines] > "on," it will spend a much greater percentage of the time actually running > in the summer than in the winter. > Yeah. Ever read newer car's manuals. Mentioned that AC will run at Defrost. > Does it put the same load on engine as cooling in summer? > > Why it needs AC? It can simply blow hot air to the front vent under > windshield. AC removes humidity. Dry air doesn't fog up as much. By the end of winter I've seen a lot of cars with miniature lakes in the floormats with mini icebergs in there, so there's a lot of humidity. Supposedly it also keeps the AC compressor seals lubricated by cycling the compressor over the winter. Ray >Yeah. Ever read newer car's manuals. Mentioned that AC will run at Defrost. >Does it put the same load on engine as cooling in summer? The AC is run is to dry the air. It won't cycle quite as much and it won't cycle at all if it's really cold. >>Yes. Defrost doesn't use any power -- it's just a vent setting. The heat >>is free. > > On many if not most cars defrost runs the AC compressor. Not when the ambient temperature is below freezing, though. > Defrost doesn't use any power -- it's just a vent setting. Wrong. For many, many years, cars with air conditioning have run the compressor and the engine's electric radiator/condenser fan when the defogger (what you are calling "defrost") is run, at least within a certain ambient temperature range. > If I just move the slider to maximum heat, but keep the fan OFF, does it > consume any gas? Not to speak of. Actually on low speed the fan consumes a minimum amount of energy. > My 94' Caravan's heater works great, in early winter I don't need to turn on > the fan. It gives out lot of hot air though. I guess it uses recycled heat > from under the hood, right? No, cars haven't used re-directed heat from the engine compartment since the early days of automobiles. Some of those early buggies had a vent door on the dash that directed heat from the exhaust manifold into the passenger compartment. Fortunately those cars were draftty so the chances of poisoning from carbon monoxide were reduced. You car runs engine coolant through a heater coil that looks much like a minature engine radiator. The fan passes air over the heater coil to extract heat. > However, I noticed a significant drop (>15%) on gas mileage each year when > temperature comes down to around freezing point. It's normal? or anything > else I can check on? Chances are your area uses gasoline that is reformulated for winter driving to reduce emissions, but the side effect is that milage goes down too. Also, in cold weather cars take longer to get to operating temperature are are running inefficiently during that time. > Thanks. The fan uses surplus electricity from the alternator. The heater uses surplus heat from the engine. There's no cost to you. I don't turn mine on until the engine starts to warm up. At first all it will do is blow cold air. Winter fuel consumption is higher for different reasons. Traction in ice and snow is not as good as summer. The engine takes longer to warm up so it idles faster. You can improve initial fuel comsumption by using a block heater. My car starts faster and idles slower when the block heater is plugged in for half an hour before starting. I don't know how to calculate the net savings, if any, of reduced fuel minus electricity to preheat the engine. > The fan uses surplus electricity from the alternator. > There's no cost to you. There is no such thing as "surplus electricity from the alternator". All power produced by the alternator costs fuel that would not be consumed if that power weren't being produced by the alternator. Greater electrical load = harder to turn the alternator = more fuel required. You're not one of these who thinks the alternator's a magical device that creates electricity from nothing, are you? > > The fan uses surplus electricity from the alternator. > > There's no cost to you. > > There is no such thing as "surplus electricity from the alternator". You beat me to the punch, but right on the nose. > You're not one of these who thinks the alternator's a magical device that > creates electricity from nothing, are you? I have yet to find the switch that disconnects the alternator belt when it is not needed. Since it is being driven by the belt whenever the engine is running, any electricity produced and not used is wasted, or "surplus". Electricity drained from the battery during peak load is replaced later unless the car is being driven short distances all the time. If the OP has to keep recharing his battery with household current, then yes, the heater would be costing money for some of the recharging electricity from the house. > > You're not one of these who thinks the alternator's a magical device that > > creates electricity from nothing, are you? > > I have yet to find the switch that disconnects the alternator belt when it > is not needed. A drycell 'battery' generates voltage all the time. If you dont draw current from it, it can last for a very long time. It dies whenever you draw all the current from it that it can produce chemically, or when the internal chemical reaction (which proceeds at a low rate even when no current is drawn) makes the cell ineffective. An alternator takes mechanical energy from the motor, and by use of electromagnetic induction, can produce current. The more current that is drawn from the alternator, by the total load of the cars systems, the more mechanical load is put upon the engine. More mechanical load reflects in more gasoline consumption. If you are tooling along and drawing nil current from the alternator, then the mechanical burden is at a minimum. Electrical current isn't wasted because it isnt being drawn. >I have yet to find the switch that disconnects the alternator belt when it >is not needed. Since it is being driven by the belt whenever the engine is [quoted text clipped - 4 lines] >would be costing money for some of the recharging electricity from the >house. This isn't the way an alternator works. Increased electrical load causes the alternator to be harder to turn thus using more energy. The alternator only produces the energy that is being consumed by the devices in the car. So while the alternator may still be spinning with no load it isn't generating electricity and isn't pulling power from the engine other than the friction load of the bearing and the internal cooling fan. Steve B. >>You're not one of these who thinks the alternator's a magical device that >>creates electricity from nothing, are you? [quoted text clipped - 7 lines] > would be costing money for some of the recharging electricity from the > house. That's not how it works, the voltage is regulated by the regulator but if there is no or minimal current being drawn the alternator requires much less torque to drive than if a lot of current is required. There is no "wasted" anything, other than frictional and heat losses. Thus demand for more electrical current does translate into more fuel burned by the engine. nate  Signaturereplace "fly" with "com" to reply. http://home.comcast.net/~njnagel >>You're not one of these who thinks the alternator's a magical device that >>creates electricity from nothing, are you? > > I have yet to find the switch that disconnects the alternator belt when it > is not needed. Since it is being driven by the belt whenever the engine is > running, any electricity produced and not used is wasted, or "surplus". That is ridiculous. The alternator just spins freely and doesn't produce ANY electricity unless the voltage regulator applies a field current to it. The power it saps in this condition is truly miniscule- just the tiny friction of the bearings and the load of its own cooling fan. When the VR does apply a field current in response to sensing an electrical load, the alternator puts many many times its "free spinning" load on the engine. So while there may not be a "switch that disconnects the alternator belt," there is very definitely a system that causes the alternator to never produce ANY more electricity than is needed by the sum total of the electrical loads on the vehicle. That's why you can HEAR the engine load down slightly when you turn on the headlamps on most vehicles. >> You're not one of these who thinks the alternator's a magical device >> that creates electricity from nothing, are you? > > I have yet to find the switch that disconnects the alternator belt when it > is not needed. Since it is being driven by the belt whenever the engine is > running, any electricity produced and not used is wasted, or "surplus". Ah, you *are* one of those, after all. There is no such a thing as "surplus electricity" or "wasted electricity" produced by an alternator. The alternator doesn't just produce some fixed amount of power regardless of the loads applied. Via its regulation system, it supplies exactly the amount of electricity demanded, up to the limit of its capacity (which depends not only on its design and specifications, but also on the speed with which it's being spun). Your guess about "surplus electricity" makes no sense, if you'd only think about it for a few seconds. Where do you suppose this "surplus electricity" would go, if the heater fan didn't happen along to use it up? By what _EXACT_ mechanism do you figure it would be "wasted"? Remember, energy cannot be created or destroyed, only transformed, transferred or stored. The alternator transforms kinetic energy (transferred via the drive belt from the engine's crankshaft) into electrical energy. The battery is a storage device that transforms electrical energy (transferred by the battery cables) into chemical energy and back again. The only "surplus" or "waste" from these processes is heat. If the alternator worked as you suppose, producing a fixed amount of electricity regardless of load, then once the battery was all charged up and there was no demand for any more electricity, all that "surplus" electricity would have to go somewhere. Two options only: 1) Heat. A typical rating for an alternator is 100 Amps, 14 Volts, therefore, 1400 watts. This is also a typical rating for a handheld hair dryer (which converts electrical energy into primarily heat). Think what would happen if you had that much heat being put out by the alternator: If you answered "The alternator would soon be a heap of slag", you're right. 2) Electricity (no transformation). If all this "surplus" electricity has nowhere to go, it'll build up until it arcs, in lightning-bolt fashion, from the alternator to whatever happens to be handy. Never seen that happen? Right, because it doesn't. Or maybe you think batteries are receptacles for endless amounts of electricity...? DS > The fan uses surplus electricity from the alternator. False (a guy with the last name "Watt" should know better! ;-) Turning on the fan lowers the system voltage, which causes the voltag regulator to feed more field current to the alternator to compensate, which then increases the load on the engine produced by the alternator- the alternator never produces "surplus" electricity. But the fan is a TINY load- GM/Toyota style high-beam daytime running lights use much more fuel than the fan on its highest setting. > The heater uses surplus heat from the engine. That is true. Usually they 'fix' the gas for the winter so we don't get as good a mileage under the pretense of 'winterizing' it. Back in the 'old' days, we got to add our own gas line antifreeze at fifty cents a bottle that didn't affect mileage... The defrost setting will use more gas because the AC system turns on with defrost to dehumidify the air. The heat you see with the fan off is just from air being forced through the system by driving. 'Most' fans these days are on low as soon as you slide the heat control from off anyway. Engines take longer to warm up which uses more gas. A block heater helps this. You can put the block heater on a timer to save electricity money because a couple hours will usually do it. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Aug./05 http://www.imagestation.com/album/index.html?id=2120343242 (More Off Road album links at bottom of the view page) > If I just move the slider to maximum heat, but keep the fan OFF, does it > consume any gas? [quoted text clipped - 8 lines] > > Thanks. > The defrost setting will use more gas because the AC system turns on > with defrost to dehumidify the air. At 15% more fuel consumption? My Chevy V8 doesnt consume 15% more fuel during the summer with the A/C on ALL THE TIME. Signatureremove MYSHOES to email > > The defrost setting will use more gas because the AC system turns on > > with defrost to dehumidify the air. [quoted text clipped - 4 lines] > -- > remove MYSHOES to email Are you stupid or something? You cut the real reason I stated for worse winter mileage and use that one line out of context. You must be a Troll or something. Dumb for sure. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Aug./05 http://www.imagestation.com/album/index.html?id=2120343242 (More Off Road album links at bottom of the view page) > You must be a Troll or something. Dumb for sure. If I were, I'd be Canadian :)) Signatureremove MYSHOES to email >> You must be a Troll or something. Dumb for sure. > > If I were, I'd be Canadian :)) English Canadian or French Canadian? > >> You must be a Troll or something. Dumb for sure. > > > > If I were, I'd be Canadian :)) > > English Canadian or French Canadian? Yes! Signatureremove MYSHOES to email > If I just move the slider to maximum heat, but keep the fan OFF, does it > consume any gas? Once the engine is warmed up, no, it does not consume any extra fuel if you haven't got the fan on. And while running the fan does consume power, it doesn't consume a lot of power from a fuel economy perspective. > My 94' Caravan's heater works great, in early winter I don't need to > turn on the fan. It gives out lot of hot air though. I guess it uses > recycled heat from under the hood, right? Not quite. Engine coolant, heated by the engine, is circulated through a heat exchanger device called a "heater core". This is a small radiator inside the car, in a box behind the dash. The hot coolant heats up the heater core. Outside air is forced through the heater core. This heats up the air. > However, I noticed a significant drop (>15%) on gas mileage each year > when temperature comes down to around freezing point. It's normal? Assuming your van is in proper repair and tune, then yes, a drop of that magnitude is normal. The engine burns more fuel when it's cold, and takes longer to warm up. Many winter gasoline formulations contain less energy than their summer counterparts -- especially those containing alcohol -- so you burn more of it to go the same distance. >.. Outside air is forced through the heater core. This heats up > the air. My heater has a lever to select between outside air or recirculated inside air, or any combination in between. It seems to defrost the windshield best set about half way. > If I just move the slider to maximum heat, but keep the fan OFF, does it > consume any gas? [quoted text clipped - 8 lines] > > Thanks. Having the heater on in some cars can increase the time it takes for the engine to warm up in cold weather since it is acting like a radiator. The gas consumption is probably due to the cold engine. I found I got about 6-8 mpg on short drives in the winter. The only appreciable energy drain is if the air conditioner is used to remove moisture from the air. > If I just move the slider to maximum heat, but keep the fan OFF, does it > consume any gas? Under almost any condition you care to name, running the heater does not waste any measurable amount of fuel, PERIOD. The engine HAS to get rid of waste heat. Normally, that waste heat goes out the radiator (even in sub-zero winter conditions). When you turn on the heater, the only difference is that a portion of that normally wasted heat now goes to the interior of the vehicle instead of out the radiator. The engine's thermostat reduces coolant flow to the radiator in order to compensate for the extra heat being lost to the heater. There are a few exceptions- if you immediately turn the heater on full-blast in VERY VERY cold ambient conditions, it will slow down the engine warm-up a bit and therefore consume a LITTLE more fuel. Not much- the mere fact that its below zero outside will cause much more fuel consumption than whether or not you run the heater immediately. But you might save a noticeable amount by driving with the heater off, or at least on low fan, until the temperature guage starts to register a little bit above minimum.
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