Car is slowly losing MPG...

[thomsbrain]

The MPG problem is pretty obviously that the OP never drives his car on a warm engine and never on an open road. I average ~21 MPG in my first 3 miles every morning, and that's a regular sedan, all downhill, with no stops. 17 MPG is actually shockingly good for a cold SUV in traffic.

 

[tortillasoup]

The MPG problem is pretty obviously that the OP never drives his car on a warm engine and never on an open road. I average ~21 MPG in my first 3 miles every morning, and that's a regular sedan, all downhill, with no stops. 17 MPG is actually shockingly good for a cold SUV in traffic.

yes that's a problem and yes that is likely causing OP's problem... but that's not OP's problem. OP's problem is that his battery is losing charge BECAUSE of everything you've said. Remember, he's here because of steadily dropping fuel economy, going from bad to worse. It's like diagnosing a person who has edema in his legs. You don't say his problem is that he's got edema because he isn't moving around and eating too much salt, you say he's got a salt retention problem causing edema BECAUSE of his diet and lifestyle. Knowing the cause of the problem can lead to the solution.

 

[leper84]

As for OP "operating in open loop", unless his car was manufactured over 20 years ago, most cars enter into closed loop within 10 seconds of start up... that's what oxygen heaters are for... (cars that don't have heated oxygen sensors take significantly longer to enter into closed loop operation.)

From looking at datastreams on scantools every day, you'd be surprised how wrong that is.

 

[compman25]

How did you drive it in Hawaii to get the 20 mpg average? Was it the same conditions? Or did you have a longer commute?

 

[LTC8K6]

The alternator is always providing all of the electrical power when the engine is running. It's hard for me to believe the varying amounts of current delivered to recharge the battery would affect fuel economy much, compared to the overall load of the whole vehicle electrical system.

 

[tortillasoup]

From looking at datastreams on scantools every day, you'd be surprised how wrong that is.

I do look at datastreams from scan tools on wide variety of vehicles all the time, that's how I came to that conclusion. Typically, a car will take longer than 10s to enter into closed if it's very cold outside, the oxygen sensor heater is aged, or finally.... poor electrical grounds! Just cleaning the electrical grounds, I was able to get a '96 Camry I4 to go into Close Loop mode in about 15 seconds compared with the 2 minutes it was doing prior. Oddly enough though, that car never had a CEL for the oxygen heater or anything for that matter but it didn't run like new either.

The alternator is always providing all of the electrical power when the engine is running. It's hard for me to believe the varying amounts of current delivered to recharge the battery would affect fuel economy much, compared to the overall load of the whole vehicle electrical system.

The load is significant because batteries are slow and inefficient at charging and alternators themselves are inefficient as well. I mean to think that only 25% of crank energy actually ends up in the battery when charging is pathetic!

 

[Nograts]

How did you drive it in Hawaii to get the 20 mpg average? Was it the same conditions? Or did you have a longer commute?

It was a shared car between my wife and I in Hawaii, she had it 90% of the time though and I would just walk to work. The closest thing I can think of was ~9 miles one direction, and my wife used it almost daily. Definately a ton more miles there, but now she has her own van and I just use the car from A to B.

Also there is obvious temperature differences. Hawaii "cold" was like 66-68 degrees. When we first got here it was like that even at night time, but since the winter time it's been topping out at these temperatures and getting down into the high 20's and low 30's.

 

[tortillasoup]

Also there is obvious temperature differences. Hawaii "cold" was like 66-68 degrees. When we first got here it was like that even at night time, but since the winter time it's been topping out at these temperatures and getting down into the high 20's and low 30's.

If it's really that cold, then that could explain the fuel economy drop.

For my sake, just check the battery voltage 20 minutes after popping the hood up and all the doors have, key away from the car (so you don't wake the computers if it's a smart key). Opening a door on the car wakes up body control modules and whatnot, putting a load on the battery and artificially temporarily lowering its voltage. If the battery voltage is 12.5< then the battery is probably alright and it's just the cold weather...end of story.

 

[jagec]

You just said a whole lot of nothing. Are you feeling alright? You remove the belt from the alternator so there isn't a load on the engine. I.e. The alternator doesn't charge the battery.

You recommended that OP put his battery on a charger overnight, not that he remove the alternator belt completely.

...although he could, with that commute.

 

[thomsbrain]

Lol, tortilla, if you had any idea how tiny of a percentage of energy usage the electrical components are, you would have stopped that utterly ridiculous alternator argument a long time ago. Since you persist in such nonsense, here's another attempt to explain it to you.

First of all, the difference between a typical 80 amp alternator with a fully disengaged field (no draw beyond pulley friction) and an alternator running at ABSOLUTE MAXIMUM draw is a whopping 1.3 HP.

Let's assume the worst-case scenario (not reality, but just to throw you a bone), that every time the OP starts his Lexus, the alternator is running at absolute maximum draw 100% of the time he runs the car.

If he drives for 10 minutes (3 miles at roughly 20 MPH), the alternator in full-panic, totally-dead-battery mode will have leeched 0.16 kW/hrs of energy from the engine.

The Honda Accord Plug-In hybrid gets 46 MPH Highway and can cover 13 miles on it's 6.7 kW/hr battery. Now, it doesn't use anywhere NEAR the entire battery because of design considerations, but let's throw you ANOTHER bone and assume it does use the entire battery to go 13 miles. To go 3 miles, it would use 1.55 kW/hr.

The Lexus RX300 gets 22 MPH Highway. We'll throw you ANOTHER bone and assume it gets 23, half of the example Accord. I'll throw you yet ANOTHER bone and assume it doesn't have any energy lost to warm-up. We'll just say he gets a staggeringly amazing 23 MPG right off the bat. That means he used 3.1 kW/hr.

That means, that even after pushing every possible variable far, far in your favor, and ignoring any variables that could harm your argument, his alternator still only would have been capable of leeching a grand total of 5.2% of the energy his car used during the commute.

The reality is, his alternator didn't run at max draw the entire time the car was on. The reality was, he used a lot more energy warming up the car and driving in traffic than my numbers assume. The reality was, his car can't get anywhere near the real-world MPG as my numbers assume, because I used highway figures. I threw everything in your favor. And still, the alternator is only a TINY percentage of overall gasoline consumption.

 

[tortillasoup]

You recommended that OP put his battery on a charger overnight, not that he remove the alternator belt completely.

...although he could, with that commute.

We were talking hypotheticals here. I was pointing out that if he were to remove his alternator belt, his fuel economy would probably jump. However, now that we have more info from OP, knowing that the temps are significantly colder than they were in hawaii. I believe the temps are playing a significant role in his fuel economy drop but he should still check out the battery voltage as he simply is not driving it enough to make up for the lost charge of cranking the engine and parasitic losses when it's not being driven.

Lol, tortilla, if you had any idea how tiny of a percentage of energy usage the electrical components are, you would have stopped that utterly ridiculous alternator argument a long time ago. Since you persist in such nonsense, here's another attempt to explain it to you.

First of all, the difference between a typical 80 amp alternator with a fully disengaged field (no draw beyond pulley friction) and an alternator running at ABSOLUTE MAXIMUM draw is a whopping 1.3 HP.

Let's assume the worst-case scenario (not reality, but just to throw you a bone), that every time the OP starts his Lexus, the alternator is running at absolute maximum draw 100% of the time he runs the car.

Why assume an 80 amp alternator when most cars are equipped with at a minimum 100a, usually around 115a+. Also, for an 80 amp alternator it's not 1.3HP load, that's 1.3HP of electrical OUTPUT. Remember, alternators are around 50-62% efficient, that's a 1548 watt LOAD for a 62% efficient alternator. For a 115a alternator that is 62% efficient, that would be a 2226 watt load at a minimum in full field mode.

Also I cite this source here: http://www.metrompg.com/posts/alternator-optional.htm

"Estimating electrical load ...

So it's clear there's some fuel efficiency benefit to be gained by fiddling with the alternator. But how much?

To figure that out, we need to start by estimating how much electrical energy is required to run the engine and accessories. Fortunately for me, Randy has already done the work. He measured the electrical power required to run his '94 Civic EX:


Item...................@ 14.4v
Idling ............... 128w
Rev up to 3500 rpm: .. +35w
Heater fan setting 1: . 55w
.. Setting 2: ......... 98w
.. Setting 3: ........ 141w
.. Setting 4: ........ 189w
Marker lights: ........ 95w
Full lights: ......... 240w
A/C (heater fan
subtracted, but
incl. condenser fan):. 163w
Defroster: ........... 104w
Wipers 1: ............. 48w
Wipers 2: ............. 76w
Radiator fan: ........ 144w"

As you can see, the electrical loads are a hell of a lot more than you think and that's for a '94 Civic.

If he drives for 10 minutes (3 miles at roughly 20 MPH), the alternator in full-panic, totally-dead-battery mode will have leeched 0.16 kW/hrs of energy from the engine.

Using a 115a alternator that is 62% efficient, it's actually 375wh. The issue with this assumption though is that the efficiency of the engine isn't linear. At idle or low speeds, increasing the load on the engine can actually make the engine run less efficiently, like less than the 20% idle efficiency, so it ends up using more fuel than you would have calculated, certainly more than 375WH worth.

The Honda Accord Plug-In hybrid gets 46 MPH Highway...SNIP
The Lexus RX300 gets 22 MPH Highway...SNIP

That means, that even after pushing every possible variable far, far in your favor, and ignoring any variables that could harm your argument, his alternator still only would have been capable of leeching a grand total of 5.2% of the energy his car used during the commute.

You're punching way above your weight class because you're throwing in vehicles, fuel economy and assumptions which have absolutely no bearing on this discussion. Let's face it, you just don't know enough about the math, fuel economy, and penalties associated with an alternator which is why you can't make a cogent argument about anything. Please, don't even bother it's pathetic.

The reality is, his alternator didn't run at max draw the entire time the car was on. The reality was, he used a lot more energy warming up the car and driving in traffic than my numbers assume. The reality was, his car can't get anywhere near the real-world MPG as my numbers assume, because I used highway figures. I threw everything in your favor. And still, the alternator is only a TINY percentage of overall gasoline consumption.

No, the reality is, we don't know a whole hell of a lot of anything because OP didn't tell us the Battery's resting voltage. It's quite simple really, if the battery is undercharged, then the alternator should be at or near full field. At this point, it's pure speculation. An alternator is NOT a "tiny" percentage of fuel consumption because what we're dealing with here are inherently very inefficient vehicles. EVEN on a Prius, the penalty of having a significant parasitic draw or a weak lead acid battery will make the fuel economy collapse from 48mpg to 40mpg.

There is plenty of discussion and evidence on hypermiling forums about the fuel economy penalty associated with the alternator and they all have similar numbers of around 10% improvement in fuel economy by removing the alternator/belt. I've even tested this sort of thing myself by monitoring the difference in my average fuel economy on my Camry from when I DO charge the battery and don't charge the battery.

Charging the battery prior to driving is as close as you can get to removing the alternator belt without removing it. The reason for why charging the battery is sort of close to removing the alternator belt is because the the battery charger/technical specification for a fully charged lead acid battery is leveling off at 14.7v before it switches over into float charge mode of 13.2-13.5v. However when my car is running, its charging voltage never reaches above 14.1v, in effect, draining the lead acid battery I had charged since the alternator field should be minimally charged.

Pretty much every car I've driven sees a pretty significant fuel economy penalty when the battery is heavily discharged, usually around 2-3mpg for a 20mpg car.

But this is all a pointless and stupid theoretical argument. It's much better just to get cold hard facts instead of throwing out useless speculative numbers out there because nobody here is capable or educated enough to make enough accurate assumptions to come to a reasonable conclusion about anything.

Fact is, if OP's battery is reasonably charged, then the answer is cold weather and possibly gumming up oil but otherwise things look normal.

 

[BUTCH1]

Based upon what research have you concluded that?

Here is a hint: An Alternator is approximately 50% efficient. When charging a lead acid battery, approximately 50% of the energy going into the battery is dissipated as heat... That means when you charge a lead acid battery with an alternator, only 25% of the energy from the crank actually ends up in the battery.

Alternators are well known for sapping about 10% of a vehicle's fuel economy and that's assuming a fully charged battery. Don't believe me? Go on any hypermiling forum and one of the things discussed was removal of the alternator belt and just charging the lead acid battery when you reach your destination.
Here is one link: http://www.metrompg.com/posts/alternator-optional.htm


This removal of the alternator belt to save fuel has been tested ad-nauseam which is why I know about it.

As for OP "operating in open loop", unless his car was manufactured over 20 years ago, most cars enter into closed loop within 10 seconds of start up... that's what oxygen heaters are for... (cars that don't have heated oxygen sensors take significantly longer to enter into closed loop operation.)

Yea, a 10% gain because the vehicle involved was a 3-cylinder 1L Pontiac Firefly, with that engine's puny output that might be the case but that hardly would apply to OP's SUV. I speak from experience of driving a 1.8L Escort for 9 years, running the AC on that car was almost like slamming on the E-brake, I had to shut off the AC when on an on-ramp to avoid getting creamed. Now I know that an AC compressor is much more of a load than an alternator ever presents, but the point is with a tiny 1L 3-cylinder engine the % of engine power needed to perform other chores, (AC, Alt., PS) is WAY more than an SUV with a large powerful V8 or V6. Also a true "closed loop" requires the coolant temp come up a bit EVEN IF the O2 sensor's are available. A cold intake manifold will not properly atomize the fuel delivered so more is needed until it is, this is accomplished by the ECU monitoring the temp. sending unit on the block or by using a timer.

 

[tortillasoup]

Yea, a 10% gain because the vehicle involved was a 3-cylinder 1L Pontiac Firefly, with that engine's puny output that might be the case but that hardly would apply to OP's SUV. I speak from experience of driving a 1.8L Escort for 9 years, running the AC on that car was almost like slamming on the E-brake, I had to shut off the AC when on an on-ramp to avoid getting creamed. Now I know that an AC compressor is much more of a load than an alternator ever presents, but the point is with a tiny 1L 3-cylinder engine the % of engine power needed to perform other chores, (AC, Alt., PS) is WAY more than an SUV with a large powerful V8 or V6. Also a true "closed loop" requires the coolant temp come up a bit EVEN IF the O2 sensor's are available. A cold intake manifold will not properly atomize the fuel delivered so more is needed until it is, this is accomplished by the ECU monitoring the temp. sending unit on the block or by using a timer.

You've conflated performance penalty with fuel economy penalty. Energy consumption is energy consumption, just because you have more energy available on tap (more powerful engine) doesn't reduce the energy consumption of the parasitic devices any more. It's like when the airlines calculated the fuel savings from disposal of the Flight bags that had 50lbs of paper and they went to all digital with the use of tablet computers.

http://www.forbes.com/sites/matthew...e-40lb-with-apple-ipad-electronic-flight-bag/

American Airlines recently got permission to use its iPad Electronic Flight Bags in the cockpit during all phases of flight, saving an estimated $1.2 million of fuel annually. (Hat tip Mactrast, image)

For pilots, it’s a huge benefit. A bag full of airways charts, airport maps and operations manuals can weigh 35 or 40 pounds. If you think your carry-on bag is heavy, try adding that for every trip.

Yes, a 747 has a payload capacity of 154 tons but that 50lb flightbag uses fuel that isn't free.

The only thing that you should have learned about the usage of the air conditioner in your Escort 1.8L engine is that everything has a cost and running the air conditioner in your car uses an immense amount of energy.

 

[LTC8K6]

BMW introduced intelligent alternator control a while ago. It basically has the alternator disconnected much of the time. It did not add greatly to fuel economy, iirc.

With the IAC system, the alternator will operate primarily when the engine has no need for power&#8212;i.e., in overrun or during braking. The alternator remains passive while the car is under power, with needed electrical power provided by the battery.

The alternator becomes active when the engine switches to overrun or if the battery charge is insufficient.

I believe many vehicles have some sort of similar alternator control these days.

 

[tortillasoup]

BMW introduced intelligent alternator control a while ago. It basically has the alternator disconnected much of the time. It did not add greatly to fuel economy, iirc.



I believe many vehicles have some sort of similar alternator control these days.

Well that's because electronics in a car do sap quite a bit of energy and also, maintaining/charging a lead acid battery in a car in quiet an inefficient process. My guess is they introduced that "intelligent alternator" so they could improve city fuel economy at the expense of likely higher battery failure rates. Honda had a similar feature in their Civic VX but there is quite a bit of difference between a Civic VX and a BMW in terms of electrical loads and whatnot. The biggest parasitic loads in a car is the keyless entry and smart key if it's equipped. Without those two things, the parasitic loads that keep the computer memory up to date aren't too bad. Had to disable the smart-key system in an LS430 and a Prius because it was running their batteries down too much, noticeably affecting fuel economy.

 

[LTC8K6]

I've been reading up, and modern charging systems are very complex. They take a lot of parameters into account to decide when and if to charge the battery, and at what rate to charge the battery, and at what voltage to charge the battery.

They even have an alternator "limp mode" if the smart control systems are not working properly.

They are very sophisticated monitoring and control systems.

 

[tortillasoup]

I've been reading up, and modern charging systems are very complex. They take a lot of parameters into account to decide when and if to charge the battery, and at what rate to charge the battery, and at what voltage to charge the battery.

They even have an alternator "limp mode" if the smart control systems are not working properly.

They are very sophisticated monitoring and control systems.

For what cars?

 

[LTC8K6]

All cars.

http://www.motor.com/article.asp?article_ID=1606

Scroll down to "Now We&#8217;re Getting Complicated"

the newer GM RVC charging systems may include up to nine different charging rates strategies, among them:

Battery Sulfation Mode. No sense hammering a battery that has given up the ghost!

Start-Up Mode. Gets the battery back up to greater than an 80% SOC quicker.

Fuel Economy Mode. Alternators that put out less voltage help engines use less fuel.

Headlamp Mode. Okay, it&#8217;s time for a little more voltage now that the lights are on.

You can also look up "Smart Charge" for Ford.

 

[tortillasoup]

All cars.

http://www.motor.com/article.asp?article_ID=1606

Scroll down to "Now We&#8217;re Getting Complicated"



You can also look up "Smart Charge" for Ford.

Cool. Sounds like Toyota is behind the curve in a lot of regards unless of course you can show me something for them as well.

 

[LTC8K6]

I haven't found docs on it, but I doubt that Toyota has passed up the efficiency gains of smart charging systems.

 

[tortillasoup]

I haven't found docs on it, but I doubt that Toyota has passed up the efficiency gains of smart charging systems.

Toyota has gotten a bit lazy in the last few years, so lazy they can't even be bothered to update the engines in a lot of their vehicles and instead are sourcing from Mazda their engines with skyactiv technology. I mean their Tundra vehicles are now the least efficient, least advanced vehicles on the market and there is nothing to indicate that it will change. If Toyota doesn't get their Prius MPG up to 60MPG instead of 55mpg, then it will be clear they just don't care anymore.

 

[Meghan54]

As for OP "operating in open loop", unless his car was manufactured over 20 years ago, most cars enter into closed loop within 10 seconds of start up... that's what oxygen heaters are for... (cars that don't have heated oxygen sensors take significantly longer to enter into closed loop operation.)

And that statement is far from the truth, even today.

Why? Coolant Temp. The ECM won't allow the vehicle to move to "closed loop" operation until the ECT tells the ECM that a certain coolant temp. has been achieved. Until the coolant gets to that temp., the ECM isn't even going to try to get into closed loop operation.

And I'm willing to bet the OP is in open loop op. until the last mile/minute or so of his drive.


As far as the alternator, you look like you're fleabagging on that, tortilla.

 

[tortillasoup]

And that statement is far from the truth, even today.

Why? Coolant Temp. The ECM won't allow the vehicle to move to "closed loop" operation until the ECT tells the ECM that a certain coolant temp. has been achieved. Until the coolant gets to that temp., the ECM isn't even going to try to get into closed loop operation.

Ok, hmm so what would that coolant temp be? I'll give you the benefit of the doubt and assume you know something that I don't. Give me an example of the coldest coolant temp that you are aware of that a car will allow for closed loop operation.

 

[BUTCH1]

You've conflated performance penalty with fuel economy penalty. Energy consumption is energy consumption, just because you have more energy available on tap (more powerful engine) doesn't reduce the energy consumption of the parasitic devices any more. It's like when the airlines calculated the fuel savings from disposal of the Flight bags that had 50lbs of paper and they went to all digital with the use of tablet computers.

http://www.forbes.com/sites/matthew...e-40lb-with-apple-ipad-electronic-flight-bag/



Yes, a 747 has a payload capacity of 154 tons but that 50lb flightbag uses fuel that isn't free.

The only thing that you should have learned about the usage of the air conditioner in your Escort 1.8L engine is that everything has a cost and running the air conditioner in your car uses an immense amount of energy.

No, YOU'VE confused energy consumption vs available total power availability which is why your 10% savings model ONLY works on tiny cars with tiny engines. Yea, headlights, fans, alternators all consume the same amount of energy but on a tiny 1L engine that electrical load is a MUCH higher % of total available power. AA might indeed save the 1.2 mil in fuel costs but that's because savings 80 pounds of weight over millions of flights eventually adds up.

 

[tortillasoup]

No, YOU'VE confused energy consumption vs available total power availability which is why your 10% savings model ONLY works on tiny cars with tiny engines. Yea, headlights, fans, alternators all consume the same amount of energy but on a tiny 1L engine that electrical load is a MUCH higher % of total available power. AA might indeed save the 1.2 mil in fuel costs but that's because savings 80 pounds of weight over millions of flights eventually adds up.

We're not talking about a 7L engines here that average 5 mpg, we're talking about a guy who has a vehicle that is suppose to average around 20mpg. 10% of 20mpg is 2mpg, 2mpg drop can easily be caused by a bad battery (not saying the battery is bad, but could be discharged).

Oh and btw, the calculated 10% fuel economy improvement on a 1.5L civic engine or 1L geo metro engine is when you go from a car that is operating normally with a reasonably charged battery to one where the alternator is completely disconnected. On a normally charged battery, the alternator isn't being fully loaded down all the time. When I disabled the smart key system on a friends Prius, due to the severely aged battery (he's using the original Prius Battery from 2004!) his fuel economy shot up from 40mpg to 47mpg which is a 17% penalty. And on a Lexus LS430, I disabled the Smartkey system which brought up the fuel economy from 17 to 18.4mpg which is around a 10% penalty. I really hate the Smart Key system and I wish it was still able to be disabled on newer vehicles.