mlody

The temp in the Midwest (Chicago) is constantly in the freezing zone for the past few weeks. I drive my TL 4 miles each way with light traffic (just few lights) and my MPG is between 15-16 MPG. Are TL’s that sensitive to the low temperature as far as mileage goes?

SouthernBoy

All ECU controlled fuel-injected cars, which covers just about everything, is going to get better fuel economy in the warmer months than in the colder months. The primary reason for this is the fact that cold air is more dense, which equates to more oxygen molecules per cubic foot. The ECU must compensate for this condition by increasing the amount of fuel delivery to the engine, otherwise an overly lean condition would exist.

Combine this with the fact that colder conditions make lubricants and grease thicker. Finally, your battery has to work harder and is not as efficient as it is in warmer times.

This is why your mileage suffers in the winter. I only get 24 MPG for my in-town work commuting in the winter.

sixsixfour

I noticed that recently too as CA got a surge of cold weather. my MPGs dropped no matter how much i drove conservatively

geekybiker

Sorta Southern boy. There is no reason why cold air by itself makes a car get much worse gas mileage. Denser air means more power which means you cruise with less throttle it more or less evens out.

What really kills mileage in the winter is different fuel blends. At least for longer drives.

What is happening with this particular instance is that at very low engine temps, fuel does not atomize properly. The ECU must use much more fuel to compensate for this poor atomization and hence the poor fuel miles (That combined with the thicker oil and lubricants that southernboy mentioned) Essentially in very cold weather and only a 4 mile trip your car is probably getting no where near fully warmed up so its always in "warm up mode"

I bet if you took a highway trip or drove over 20-30 minutes at a time you'd see you fuel mileage come up way closer to normal.

<-- programed ecu fuel maps from scratch for stand alone ECUs.

sunny201

WOW i was thinkin the same exact thing, but I thought i just developed a bad case of lead foot syndrome... but good to know its not me and its the weather

6spMike

The short trips have got to be the number one contributor.

lusid

Minnesota here, I've gotten the worst tank yet maybe...

19mpg (according to the car pc) 200miles driven this week.

This was with 2hrs of traffic to go 20miles.

Lowest temp was -10 i believe.

SouthernBoy

Colder air is more dense, hence a greater amount of oxygen content. What this does in your engine is cause an oxygen rich mixture. The OX sensor reads the increased heat cause by this condition which the ECU interprets and therefore adds more fuel to the intake stream in an attempt to maintain the optimum fuel/air ratio.

You are certainly correct in your statement regarding more power due to these factors. In fact 20+ additional HP with an accompanying increase in torque is not unusual (depends upon cubic inch displacement and state of tune). As for cruising with less throttle, yes, more power tends to help in some conditions such as load, hills, etc.

When I lived in Arlington, oxygenated fuel was sold between the months of November and the end of February. When I had my '88 Mustang LX 302CID, I recorded a 14% drop in fuel mileage during those times, with the attendant increases in power.

While it is true that fuel does atomize better in warmer surroundings (ambient atmosphere, intake manifold runners, plenum chamber), when it enters the combustion chamber and encounters the heat therein along with the swirling effect of the chamber design, atomization has taken place quite well.

I would guarantee that if you drove a TL for, say, 50 miles to really get all the parts and lubricants good and warm, and then did a careful fuel mileage test, you would find that in the cold, your car would get less mileage than in the warmer times.

While I personally detest the winter months, I do love the added power.. mileage be damned.

Elegant TYPE S

iTrader: (2)

Yeah but in the colder temperatures that you realize this, if you live in the NE deosnt gasoline we use contain 10% Ethanol? Meaning that our Gas mileage should decrease by 10%?

Parker75

Knowing this to be the case, doesn't it make sense to preheat the intake air? We don't see this on cars sold in markets that experience cold weather, and I wondered why that is?

I agree. Last week I made the same 200-mile round trip on two days (Feb 1st and 5th) with very different ambient temps. The temperature difference was ~20 degrees and my TL computer reported a hwy trip MPG difference of 3 MPG less on the colder day -- 29 vs 26.

Even for non-hwy driving, I see about a 3 MPG difference with the colder temps: 23 vs 20.

When it gets cold enough to turn spit into ice in a few seconds, I don't think the added power is a useful advantage. With the possibility of ice on the road, I tend to go easy on the power. For me that added power in cold weather is unnecessary.

SouthernBoy

Preheating the intake air stream may seem like a viable alternative, however the ECU does an excellent job of monitoring and adjusting ignition and fuel delivery as it is. Many years ago, a lot of cars (as in V8's in the mid 60's) had "heat risers" built into their intake manifolds to prehear the manifold as an aid to "better" fuel atomization and combustion (remember, these were carburetor cars). It was common in the rodding circles to use heat riser blockers to remove this effect in order to produce more power (Royal Oak Pontiac offer these in a kit for GTO's). I would not suggest this with today's cars because of the precision of current ECUs.

I commonly see in the neighborhood of a 2 MPG drop in fuel economy in the winter as opposed to the summer when commuting back and forth to work.

As for the "more power" thing.. what can I say. I'm a gearhead and more power is ALWAYS a good thing in my book.

SouthernBoy

I don't know since I live in the South. I guess I'd better take a look at the pumps around here to see if ethanol is being added to our gasoline. I do know that when I lived in Arlington, as I mentioned previously, stations there sold fuel that was oxygenated with, I think, benzene (not really certain of this one). The affect was lower mileage (I said 14% in my Mustang), but noticably more power.

This is the same thing we see with NOS after-market systems in cars. Nitrous oxcide increases the ozygen percentage in the cylinders thereby requiring greater fuel delivery. More fuel in an ozygen-rich environment means a lot more power.. and more heat to help destroy things like valves.

Mike 06 TL

I drive 110 miles roundtrip to work everyday, 95% highway. In normal temps I get a consistent 30mpg at 75mph. Over the last few weeks it has been between -2F and 10F everyday and I'm getting 28-29 mpg...not much of a drop off.

I use Sunoco fuel which already contains 10% ethanol all the time...winter or not.

Parker75

I think you are saying that the ECU has done all the optimization to get the best fuel efficiency possible with freezing ambient air temps. I agree given what variables it has to control. But considering that even you experience a 2MPG drop when it is cold seems to imply that more could be done.

What I was suggesting is the idea of preheating the intake air for the express purpose of avoiding the drop in fuel efficiency with frigid temps. I'm not interested in the extra power but I am interested in avoiding the drop in my MPG by 11-14% (from 23 to 20 city, 29 to 26 hwy) during these cold times.

Of course I realize there are other factors contributing to the drop in MPG with sub-freezing temps. But as far as the engine is concerned, it seems to me that preheating the intake air from sub-freezing to warmer temps would help keep the MPG as high as possible.

Is this idea pre-heating viable to avoid the MPG drop with cold temps?

leedogg

There might be a few fuel additives you can add that might help...like drygas.

01tl4tl

Driving 4 miles is barely getting the car warm- so the fuel injection sensors are running at full rich mixture instead of their normal lean clean machine setting

Drive more- get better gas mileage

SouthernBoy

It may be possible that you might see a slight increase in mileage with a pre-heated intake manifold, but I'm not so sure that would not be offset by other factors.. such as thickened lubricants and greases among them. This might be an interesting experiment for someone to take on. My guess is that not only the manifold runners and plenum would need to be heater, but you would also want a "heating" screen added in line between the air filter and the throttle body.

Frankly, I would doubt if the effort would be worth it since there a a host of other variables at play here. But what the hey.. anything's worth a try.. right?

Parker75

Yes, it is worth a try. And yes, I agree that there are other factors involved such as the thickened lubricants with lower temps.

It certainly would interest me to know what is the effect of changing only the intake air temp while keep other variables the same. Unfortunately I don't have the facility to perform the test but I would imagine such a test had been done before. I guess I will have to scour the Internet for any paper on this topic.

SouthernBoy

Good idea. Please report back what you find.

leedogg

Do you let the car warm up before driving? In addition to dry gas, I would add chevron's fuel cleaner.

SouthernBoy

Shouldn't need dry gas unless the tank is being allowed to run down close to empty. Should always maintain at least 1/2 a tank in the colder months.

Chevron's Fuel System cleaner is a good thing to do every 10,000 miles or so.

As for warming up an engine, I would keep this to a minimum (maybe 30 seconds), then just start driving carefully until the temperature gauge gets up to the normal range. That's the best and quickest way to warm up an engine.

geekybiker

Sure, but not because the air is cold. That might be a minor factor though. Fully warm in the winter, the fuel mix will probably be the biggest culprit in fuel mileage differences.

Lets show it though.



Pd=pressure of dry air.
Tc ambient temp, deg C.

So for simplicity lets say sea level to leave pressure out of it, and use -10c for the cold weather in chicago (from the OP) and a nice warm 20c day.

on the -10c day cf= .9285
and the 20c day cf= .9900

So we are talking about a 6.15% increase in power, with a corresponding increase in fuel usage. EFI once warm will maintain the fuel ratio for the density of air.

So by your theory 30 mpg would become 29.7mpg at 20C and 27.855 mpg at -10C. Thats a pretty minor difference. (and since our cars get closer to 22-23 more typically the difference is even less) BUT you will need less throttle to maintain your speed in almost all situations (unless you're really cruising at idle) So your fuel saving will be somewhat less than that.


There is also the fact that in very cold temperatures your radiator may be overly effective and not allow you engine to reach optimal operating temp. Ever wonder why semi trucks have those bras over their radiators in cold weather?

leedogg

That might be because diesal engines are more susceptible to the cold temperatures when they need to startup.

weedeater

Running cold like this, the ECU is running the engine richer longer to heat it up as soon as possible. And heat the CAT.

SouthernBoy

Actually a leaner mixture runs hotter than a richer one. That's how the OX sensor works. It reads exhaust temperature and adds or reduces fuel delivery and adjusts timing based upon the temperature of the exhaust stream.

sixsixfour

true.

when the engine is cold, the ECU delays the flow of coolant through the engine's water passages to hasten the warm up of the engine.

if the engine is running lean and when the O2 sensor picks it up, the ECU is designed to inject more fuel to "cool" the intake charge and pull timing. you actually lose power when more fuel is dumped because efficiency is lost.

Buda

iTrader: (1)

I'm glad someone else noticed this. Here is what I just experienced.

In November I drove from Minneapolis MN to KC and back, weather was 30 degrees in MN and 50 in KC. I got 31.8 mpg by gas receipt and 30 mpg by MID. I made the 450 mile trip back to MN on a single tank of gas!

I just drove down to KC from MN yesterday, temperature was 0 to 6 degrees for the whole trip. Not sure what the mpg by receipt was, but the MID showed 25 mpg!!!! Needless to say I had to stop once for gas. I was sooooo irritated that my mpg dropped so much.

Other factors to consider:
1. Just got oil changed at dealership on Tuesday night.
2. Car had 6k miles before trip. Trip was 450 miles.
3. I checked tire inflation before trip, it was:
34 - 33
32 - 32

meowCat

Isn't starting my TL in the cold winter bad? I wonder if it's hurting my engine. It's about freezing point here. SHouldn't I be using synthetic in this kind of weather? I don't care about gas mileage. What I care about is the car.

geekybiker

Nope.
An oxygen sensor is not a tempeture probe. It compares the gas composition vs a reference gas (outside the exhaust tube)

If you're really interested
http://patft.uspto.gov/netacgi/nph-P...S=PN/3,933,028

You can make certain assumptions about air fuel ratios via a tempeture probe, but they work differently.

SouthernBoy

Oops. Did I blow that one or what? Please pardon my ignorance.. I had honestly believed an OX sensor read exhaust gas temperature and made its adjustments accordingly (leaner mixtures being hotter than richer mixtures).

I stand corrected and apologize for my error, gentlemen.

SouthernBoy

Not at all. While it's true that a little more caution would be prudent (driving easier the first 3-5 miles would be good), you car will do just fine in the colder weather. Beside, freezing in only 32 degrees and that is not all that cold when you think of it.

As for synthetic (oil I presume), this is a good choice regardless of the outside temperature.

SouthernBoy

BTW.. you wouldn't have a washcloth handy so that I can wipe all this egg off of my face, would you?