cold weather economy mod?

I have a 2000XJ Limited; so naturally, I'm always screwin' around with the trip computer . I noticed that (in Michigan) my gas milage really dropped (2-3 mpg) recently with a deep cold snap. Then the temps rise 10 - 15*F and the economy picks back up too.... I have a homebrewed air tube with a K & N style cone-shaped air filter feeding it. I noticed that the tube is cold when driving, so I know that the corner of the engine compartment that I put it into is getting outside air.
I'm wondering if....I took my intake air right off the backside of the radiator in the cold months and piped it right over to my old stock airbox, if the warmer air would help the fuel economy....and possibly the power?? Of course, I would change back over to airtube setup in warmer weather .
Anybody done this yet?
BLUTO

Spending a fair amount of time around race cars or street strip type cars, I've heard quite a few discussions about intake engine temp.

The easiest response to your question is, Yes.. This would make a difference.. but.. there is a very happy medium when it comes to intake temperature..

That is why they sell cool cans (ice boxes for intake tubes), intercooler NO2 coolers (for turbos) and (also recommend intake warmers for diesels that run in arctic temperatures, -20 and below Fahrenheit)..

It's a hard thing to figure out what intake temerature your specific engine runs the best in, and sadly it's a 15 degree spread..

Commonly while you are driving your intake temperature in spring, summer, fall and winter never tend to vary more than 15-20 degrees usually staying within the 15 degree span you've got as far as optimal intake temperature..


One way racers figure this out is through multiple sessions or long sessions at a dyno.. They install a intake temperature sensor in the intake tube, figure out what temperatures they're looking at and find the most performance at whichever termperature they're running at.. and from there they have a pretty decent figure to judge with.

In my honest opinion.. I think trying to figure out what your most optimal operating intake temperature to run at is, mostly a waste of time.

It's one of those things that most people don't notice, because they tend to run dry gas, octane boosters, injector cleaners, slick 50 fuel injector treatment, and other various dump in the tank products to make sure their car doesn't die in the winter months and just take the 2-3 mpg loss as a normal loss..


Another theory in regards to the loss in mileage is that in Winter, temperatures get colder.. Intake temps get colder.. Fuel becomes more dense and so does the air.. Therefore allowing a larger more dense combination of air/fuel mixture... This would seem like another commonly accepted solution and probably makes more sense than the first, but.. in turn this should note slight gains in torque and horsepower all across the range.. when I say slight I mean 1-3 hp..

The denser the charge of the air or the fuel the more of both it can fit in the cylinder and therefore the more power it can make.

The more power the motor makes the more fuel it uses..

I hope this helps.. I know it's a long reply, but.. You're making me think back through 8-10 years of learning..

Bill

So, this recent cold front that hit the southeast and texas (I dunno where else it went) that took temps from 80 to 35 in a matter of days would explain why I got terrible gas mileage on my last city-tank and why it went steadily up as I drove east and the temperature rose? I got 10 mpg in town (I usaully get 15, even with the AC blowin', in town) and 19 hwy. I got 16,17,18 mpg in that order, on the trip east.

With no ac running, it should go up 10% or so. I don't recall my mileage being this bad last winter (only had this truck for ~15 months). Could the sudden change in temperature just confuse the computer perhaps? I'm just hoping it will go back up, since I can't afford 10 mpg!

cold weather economy

Today the ambient temperature is 50-55*F and my milage is at it's peak (~18mpg @ 70mph....3.55 gears and 30.25" tall tires - needs a re-gear). But, when the temps fall to 30*F or less; that same 18mpg becomes 15mpg . I can't really feel any change in power?
I just sold a twin-turbo Dodge Stealth this spring...it loves cooler temps! You can definately notice a power difference at 50*F vs 80*F .
I was looking at the front of the engine, not a lot of room to put anything between the radiator and the front of the engine . If I can come up with some type of homebrewed warm air diverter and it works, I'll post it here.
BLUTO

The colder the air, the more fuel the computer injects. You could find out what temp. is optimal for power then do a resistor trick to your IAT and tell the comp it is always that temp.

This entire discussion seems way out in left field.

Cold air is denser than warm air. In a carbureted system, colder air results in a leaner mixture, unless the carb is re-jetted to compensate. A leaner mix should equate to better mileage, not worse.

However ...

We run computer-controlled multi-port fuel injection. The oxygen sensor continuously monitors the air-fuel ratio and sends data back to the ECU to adjust the mix, maintaining it at or very close to stoichiometric optimum.

It's more reasonable to hypothesize that your drop in economy is due to the probability that you still have the "summer air" in your tires. Yes, it's an old joke -- but when the temperature drops, so does your tire pressure, and softer tires require more fuel to push.

USE A SCREEN ON FRONT GRILL (when its really cold)

Helps to keep temps stabile when runnibg on HWY...
I used it when we had 25 outside ...did the trick!

That's what I thought was my problem... after the 10mpg tank I checked and my air pressure had dropped a whole 5 psi, so I aired them back up at the next stop (this was the stop when I got 17 mpg) but the stop after that mpg went down to 16. It is possible I was heading into the wind, but it didn't feel like it.

I know sudden changes can confuse computers - can it react quick enough to temp drops like a cold front?

btw - my original post here had the wrong order for mpg, the first stop was 17, then 16, then 18. not that it really matters, but some of you might catch the contridiction between the posts...

Eagle said:

The oxygen sensor continuously monitors the air-fuel ratio and sends data back to the ECU to adjust the mix, maintaining it at or very close to stoichiometric optimum.

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Ya old fart. You beat me to it.

A SPOBI call was waiting in the wings.

Some other issues with winter driving include extended warm up periods, lots more stop and go driving and increased aero drag thru that heavier winter air.

Whatever the science , my gas milage goes to crap in midwest winter running w/an air snorkle... i probally loose an easy 3 miles to the gallon when we are down in the 20-30 degree area.

This is stop and go to a from work and i dont warm the jeep up much. So Im not changing anything other than the temp outside.
One problem in the midwest is the switch to "winter" gas, it sucks and is known to give you less miles, another reason why the price drops when they switch blends.

regards
chewy

MaXJohnson said:

Ya old fart. You beat me to it.

A SPOBI call was waiting in the wings.

Some other issues with winter driving include extended warm up periods, lots more stop and go driving and increased aero drag thru that heavier winter air.

Click to expand...

ChEwBaCcA said:

One problem in the midwest is the switch to "winter" gas, it sucks and is known to give you less miles, another reason why the price drops when they switch blends.

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You pay less for that weasel pee? Here in the northeast they make us run that stuff in the winter, too, but we get to pay MORE for it

ChEwBaCcA said:

Whatever the science , my gas milage goes to crap in midwest winter running w/an air snorkle... i probally loose an easy 3 miles to the gallon when we are down in the 20-30 degree area.

Click to expand...

The reason for the gas mileage drop is very simple. If your engine is inhaling very cold air, it takes longer to warm up so it spends more time running in rich mode. If you only do short journeys, the drop in gas mileage will be even more noticeable.
There are some things you can do to remedy that, and all involve attempts to make the engine warm up faster so that the PCM goes into closed loop mode earlier. The first is to route some warm air from around the exhaust manifold to the airbox. Secondly, you can install a Robertshaw 205* t'stat in place of the stock 195* version. Thirdly, you can block off part of the grille with a piece of aluminium foil so less air goes through the radiator. Make sure your tires are also properly inflated to reduce rolling resistance.
Finally, if you have a lift, bigger tires than stock, and are carrying extra weight, don't expect good gas mileage. If you remove some unnecessary weight, that might help.

Dr. Dyno said:

Secondly, you can install a Robertshaw 205* t'stat in place of the stock 195* version.

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Dino, it's lucky for you you live FAAAR away. This is the forum where almost everyone claims the answer to every XJ problem is to run a 165 degree thermostat ... and now you chime in recommending a 205?

HERESY. BURN HIM AT THE STAKE!

:anon: :firedevil :twak:

What do you meen SPOBI? Am I incorrect in thinking that the colder the air, the more air enters the engine because cold air is denser? As a result of this the computer dumps more fuel in to even out the Air/Fuel mixture. If you want the engine to run a little leaner for better gas mileage you can mod the IAT or you could install an adjustable MAP. If I'm out in left field on this one tell me. Wouldn't intalling a block heater help the long warm up problem?

Eagle said:

Dino, it's lucky for you you live FAAAR away. This is the forum where almost everyone claims the answer to every XJ problem is to run a 165 degree thermostat ... and now you chime in recommending a 205?

HERESY. BURN HIM AT THE STAKE!

:anon: :firedevil :twak:

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It's nice to know somebody agrees with my wisdom. If you were living in temps. of less than 30*F and you wanted to get the engine to warm up quickly so you could turn on the heater and defrost your fingers, which thermostat would YOU or anybody use?

CW. said:

What do you meen SPOBI? Am I incorrect in thinking that the colder the air, the more air enters the engine because cold air is denser? As a result of this the computer dumps more fuel in to even out the Air/Fuel mixture. If you want the engine to run a little leaner for better gas mileage you can mod the IAT or you could install an adjustable MAP. If I'm out in left field on this one tell me. Wouldn't intalling a block heater help the long warm up problem?

Click to expand...

CW, the SPOBI comment wasn't necessarily directed at you. When you start messing with sensors, the O2 sensor with fight you all the way. Try to lean out the mixture more than the computer likes and it will increase the injectory dwell to compensate. Dino can get away with some of these tricks because IIRC, he doesn't run an O2 sensor.

You also have to consider that if your engine is using more fuel to make more power with all this cool air, you will have less need for a heavy throttle foot. Less throttle = less air = less fuel. It all evens out.

cold weather economy

OK! OK! so cold weather driveability can be affected by tire pressure, thermostats, trip duration, IAT, MAP, O2 sensors, and grille covers. On a lot of older GM products, they had thermostatically-controlled intake air heaters on the air filter box that drew hot air off the surface of the exhaust manifold. This would raise the intake air temps on cold start-up and cold ambient conditions. My thoughts are, if you could manage to sqeeze a "DUCT" between the engine and radiator (or somewhere there is warm air flow) then funnel that > stock air box > engine. If you can make the IAT sensor "see" warmer air, then it should recalibrate to get better milage.
Obviously, this is a "cold weather only" mod
BLUTO

RENIXII xj's came with exactly what you are talking about. The exhaust manifold has a dict coming off of it that goes to a valve on the airbox. You could swap in a renix manifold and airbox in the winter, it's not hard at all.