hot air intake for better MPG?

My 91 drops off a few MPG in the colder months.

I was wondering if adding a hot air intake to the air box would help. The intake is unheated on this year of 4.0L.

I thought of making a small shroud that would hold one of those aluminum intake hoses on the header. Then make another hole towards the rear of the box and partially block the front intake.

Andy

While it'll warm the Jeep faster, you'll notice the throttle body and intake being dirtier with all of the exhaust getting pumped back through.

A remote starter would be better. I got one for $90.00. Just remove your lower dash panel and all of the wires will be there.

my mileage goes up when the temp goes down!! It may be that they're now selling you "winter" gas instead of "summer" gas.

keep in mind many gas stations have additives for winter driving added to their gas, which reduces milege a bit.

dang it too slow
see above

Yea mileage always goes down with winter gas for us.

exhaust getting sucked back through????

I am talking about adding a hot air intake to the engines air intake box.

It would just be sucking air in from around the header to warm the air before it goes into the intake. Most all of my older vehicles have this. Almost all older vehicles also have heated intakes (via exhaust or coolant).

I can't link it to the gas. A tank I bought a week ago I got 20mpg, the latest 17. I keep a log with ever tank full in it, I can trend MPG vs temp pretty easilly most of the time. Last winter it usually got 16.5 average over the cold months.

Andy

I'm working on proving that cold air reduces gas mileage.

I've been running experiments as the temperature drops.

Just wait, and I'll have my own thread.

A sneak peek: most data I have so far indicates that cold air decreases gas mileage measurably.

j99xj said:

I'm working on proving that cold air reduces gas mileage.

I've been running experiments as the temperature drops.

Just wait, and I'll have my own thread.

A sneak peek: most data I have so far indicates that cold air decreases gas mileage measurably.

Click to expand...

exactly!

Cold air is good for power, as the computer sees the lower temp with the IAT (or the leaner output of the 02 sens) and puts in more fuel to keep the mixture in check.

Warm air needs less fuel. Also fuel atomizes better in the warmer air.

Post a link to your stuff here once you do it, that way I will get a notice so I will know :guitar:

j99xj said:

I'm working on proving that cold air reduces gas mileage.

I've been running experiments as the temperature drops.

Just wait, and I'll have my own thread.

A sneak peek: most data I have so far indicates that cold air decreases gas mileage measurably.

Click to expand...

could it be that the fuel is also colder and thus it takes the engine more work to heat up/vaporize and burn the fuel then it would at a hotter temp?

j99xj said:

I'm working on proving that cold air reduces gas mileage.

I've been running experiments as the temperature drops.

Just wait, and I'll have my own thread.

A sneak peek: most data I have so far indicates that cold air decreases gas mileage measurably.

Click to expand...

Maybe so - but be sure to correlate for the effects of extra oxygenates added to fuel in wintertime (anything you add to a fuel that isn't itself fuel is either a diluent or an adulterant - and you'll reduce power output as a result.)

'Way back when, I did note that fuel economy dropped off slightly in my Bug during the wintertime (this was before "Winter Gas" in Indiana,) but power also improved slightly (measured as 0-60 times.) Even with a carburettor, the increase in air density due to lower temperatures will tend to consume a bit more fuel (making more power.) This would be more noticeable with fuel injection, since more account for air temperature and density is made.

However, "winter gasoline" tends to exaggerate the effect of this, for the reasons stated. A true "apples to apples" comparison would be to use the same fuel for tests - same batch - in winter and summer.

And, unless there's a crack in the exhaust manifold, you're not going to get exhaust recirculation using a "choke stove" (that's what it's usually called.) Crapping up the intake stream is, however, an effective argument for the elimination of Exhaust Gas Recirculation (EGR) - my intake looks like midnight in a coalmine...

in the cold and winter months you use your headlights, defroster(which uses the A/C fan and system), thus working your electrical system harder. which causes higher fuel consumption. you use more gas driving at night than during the day also.

Bear in mind the earlier XJ's with the preheat (like my'88) have a temp sensor in the air box that controls the diverter. Once the engine bay warms up enough, the valve directs "fresh air" from behind the headlight into the airbox.

If you replicate some kind of diverter that switches either automatically or manually, I can't see how that going to make much difference since the heated air supply is short lived. If you don't or leave it "hardwired" to hot all the time, I'd love to see the effect all that hot air has on your airbox, intake and engine after a while. The temps coming off that part of the manifold must be 400 deg or more when fully hot.

Cold air from where? A snorkel...yes. Anything under the hood (warm). I have a cone filter, but its under the hood=warm air just less restrictive intake for the engine. In my 95 Trans AM, I have a fenderwell intake system from K&N and that may draw in colder air. All with a cone under the hood are not getting colder air than you would have with a stock airbox, very minimal difference if any temperature wise.

Winter gas...bad for MPG freaks (anti-gel ingredients).

Take a temp reading under the hood while driving in the winter, it's not that hot.

I will experiment with it if I get time.

Again, not talking about EGR. Talking of building a shroud around the header to draw the intake air past the header tubes before it goes into the air box.

It might not be enough to help, but worth a try when gas around here is 3.30 something now.
Maybe I should just switch to propane :rof:

Andy

As a few folks have stated, 'winter' gas is a little more volatile- it ignites more readily to help get you started on a cold morning, but it also evaporates quicker (I know there are evap. systems, but better to go thru the injectors than a vac. hose as vapors). Also, don't forget the dense, heavy, usually moisture laden cooler air that you're trying to push your brick- shaped vehicle through.

cone or stock filter, it still takes air from the same area. Winter gas is the biggest factor in all of this

maybe2fast said:

cone or stock filter, it still takes air from the same area. Winter gas is the biggest factor in all of this

Click to expand...

Not so.

When I started my experiment (in Aug., hence summer gas) I still found a lower mpg when testing at night (20-30 degrees cooler).