Can somone explain this please::

I searched around for this, couldent find the thread i was looking for. Im curious about the "Hot air baloon effect" and how keeping the heater on gets you better fuel ecconomy. I remember seeing it around (within a 3 weeks) but i cant seem to find it.

it means dont keep the heat on high for to long or you will float away

well driving with the heat on in some vehicles will take heat out of the engine and throw it into the cab, cooling down the engine compartment.. wether the cooler running motor gets better fuel ecconomy or not i dont know

i thought the heater took ait out of ducts right infront of the windshield and not through the engine.

But the extra current demand of the blower motor (on the alternator) will decrease your fuel economy. Remember there is no free lunch whenever thermodynamics are concerned.

Thermodynamic engines will a: produce more heat than is produced by combustion alone, b: not convert all of the heat energy into motion.

The engine is still producing the same amount of heat and probably the same combustion temps, the heat is just going somewhere else. Of course, you can radiate some heat away through the heater core (no blower) which may slightly lower underhood temperatures but I thought engines were more efficient when hot. Using the heater when ascending a grade on a hot day, I thought was an added measure to prevent overheating.

I was thinking along the lines that when the cabin of the jeep is hotter than the air outside you are lighter. Like a hot air baloon.

While the logic is correct, you are talking about:

a.) a relatively small amount of air (compared to a hot air balloon) in your XJ,
b.) relatively small difference in temperature compared to ambient.
c.) Steel, well in excess of 1 ton. Your XJ is heavier than a balloon basket.

My vote, you are really more likely to cause a decrease in fuel mileage due to the extra current draw, and (this is a strech) extra energy required to pump through the heater core.

helix said:

i thought the heater took ait out of ducts right infront of the windshield and not through the engine.

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the heater ducts have a heater core inside of them with engine coolant flowing inside it. The blower motor pulls the air through it, so with the heater on it acts as a small radiator removing heat from the engine into the passenger compartment

From my own un-scientific test: Outside air 45F, heat on, blower on high (notch 4) the temp gauge on the dash drops from 210 to about 208. not worth the extra power drain, not to mention the noise. use it only if you're overheating and trying to get home.

Something to consider...Ok so you know how superchargers work right? they force cold air back into the intake to lower air temperatures. While this doenst pertain to heat it does pose a question. haha. but anyway lowering the air temperature allows the fuel and oxygen to combust better thus creating more horsepower. So what if you hooked up a piping system from your vents and ran your vents from your a/c compressor directly into your intake. Would that make a lot more power? just something to consider

leftyatm said:

Something to consider...Ok so you know how superchargers work right? they force cold air back into the intake to lower air temperatures. While this doenst pertain to heat it does pose a question. haha. but anyway lowering the air temperature allows the fuel and oxygen to combust better thus creating more horsepower. So what if you hooked up a piping system from your vents and ran your vents from your a/c compressor directly into your intake. Would that make a lot more power? just something to consider

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The purpose of a supercharger/turbo is to make the air more DENSE. as a side effect of compressing the air, you get heat. this heated air is sometimes run through an intercooler to remove some of the heat, thus making the air charge more dense. yes, cold air is more dense, but Superchargers do not cool the air! if anything, they make it hotter.

as to the A/C thing. the extra drain caused by running the AC non-stop will negate any benefits of colder air. If you want to cool the air, install a cold air intake (and make sure it gets cold air, not just heated engine compartment air), or a snorkel. here in the winter, naturally cold air would be much better than anything you could get from the AC.

Haha i know... it was always something a buddy and i tought about. Just a stupid little idea to save 4,000 dollars for a supercharger combination LOL

Ever notice gas coming out of tires (or better yet a pressurized cylinder) is cold, the opposit is true with compression and a turbocharger or supercharger will in fact, heat the air up more than compressing it alone will. This is due to heat transfer from the exhaust side (turbos) and friction produced by moving parts and moving air. If you talk about using a/c chilled air, its the same way. A/C systems produce more heat than they remove from the air, due to friction. Therefore, an a/c cooled engine air would never be beneficial, the extra energy gained from denser air would be lost to produce the cool air AND then you lose some more power due to the inefficiencies of the system. Remember thermodynamic machines are inherently inefficient, there is no free lunch. This is all basic stuff I remember about thermodynamics from high school physics.

Forced air induction allows you to mechanically put compressed, denser air into the cylinders so that you can get more O2 AND fuel into the same space = more power. Intercoolers are used to get the compressed air back down to ambient levels though its still probably hotter than a non-turbo engine. In fact, if you are going to be putting a super or turbo charger to a car that wasn't designed for it, you need to take the extra heat generation into consideration and plan to modify the cooling system appropriately.