Fuel mileage

[lbroer]

Got my 2007 Touring in May and was averaging about 25.5 mpg in warm weather. After cold weather settled in I am getting 22.5 mpg on average. Is this difference normal?

[TrailDust]

Changes in winter and summer blends of gasoline can account for 10% differences in mileage. Also, any changes in brands of gasoline can make a difference as gasoline is only as good as the chemical engineers who test and tweak the blends.

TrailDust

[kraky]

Agree...10% drop not surprising.....ALSO BE SURE your tire pressures are up....if they haven't been checked they will certainly be low.

[lbroer]

Originally Posted by TrailDust

Changes in winter and summer blends of gasoline can account for 10% differences in mileage. Also, any changes in brands of gasoline can make a difference as gasoline is only as good as the chemical engineers who test and tweak the blends.

TrailDust

Thanks guys. Fuel blends might be the answer but I'll check my tire pressure as well. A 10% change in fuel btu content might be the answer but that is a big change. I generally buy my gas from Marathon who I think does not add the ethanol garbage that the politicians and the corn farmers are requiring.

[Amaury]

Originally Posted by lbroer

Got my 2007 Touring in May and was averaging about 25.5 mpg in warm weather. After cold weather settled in I am getting 22.5 mpg on average. Is this difference normal?

Because it is harder to start your car in cold weather, you’ll see a drop in fuel efficiency. Once the engine & other elements reach operating temperature (temperature gauge in your dash is half-way), fuel consumption resumes to “normal”.

When starting a cold engine in cold weather:

• Your gasoline evaporates less, so it becomes harder to burn it. Somewhere along a chain of events due to this condition, your engine management system may ask for more gas to compensate for the weak combustion.
• Your engine oil gets thicker, making it harder for the engine to spin. The harder your engine revs the more gas it uses (under this effect) to overcome this extra friction.
• Your transmission fluid temperature is way below normal, forcing your tranny to remain longer in lower gears.

Lower gears = high gear ratios = high engine revs = more gas (in this case).

And remember, all this (and other factors) is taking place simultaneously. So, the hotter your engine remains in cold weather, the better your fuel efficiency will be.

Amaury
'08 Limited

[TrailDust]

Originally Posted by lbroer

Thanks guys. Fuel blends might be the answer but I'll check my tire pressure as well. A 10% change in fuel btu content might be the answer but that is a big change. I generally buy my gas from Marathon who I think does not add the ethanol garbage that the politicians and the corn farmers are requiring.

You might find out which refinery Marathon gets its gas from. Sometimes that can be difficult as even major brands of gasoline will buy product from each others refinery. When you find a brand/station that burns well, stick with it. Even if it's more expensive you can still come out ahead. Just a couple years ago everyone was telling me Costco had the cheapest gas around (which it did) so I tried it. My mileage became so terrible I monitored it for two tanksful. The result: a drop in mileage of 15%. I went back to using my normal gas station/brand, and even though it was more expensive the increased mileage much more than compensated for the price differential. Food for thought.

[lbroer]

It's hard to know where they get their fuel. The folks who barely speak English here probably won't understand the question if asked. Wish I could have API gravity data for summer and winter fuels. We don't buy fuel by the BTU content. We pay by the gallon. If they sneak in a lot of ethanol you are getting less BTU's and less mileage.

[lbroer]

Originally Posted by Amaury

Because it is harder to start your car in cold weather, you’ll see a drop in fuel efficiency. Once the engine & other elements reach operating temperature (temperature gauge in your dash is half-way), fuel consumption resumes to “normal”.

When starting a cold engine in cold weather:

• Your gasoline evaporates less, so it becomes harder to burn it. Somewhere along a chain of events due to this condition, your engine management system may ask for more gas to compensate for the weak combustion.
• Your engine oil gets thicker, making it harder for the engine to spin. The harder your engine revs the more gas it uses (under this effect) to overcome this extra friction.
• Your transmission fluid temperature is way below normal, forcing your tranny to remain longer in lower gears.

Lower gears = high gear ratios = high engine revs = more gas (in this case).

And remember, all this (and other factors) is taking place simultaneously. So, the hotter your engine remains in cold weather, the better your fuel efficiency will be.

Amaury
'08 Limited

Amaury,

Cranking is a small percent of time in my overall operation so that probably is not part of the equation. Transmission shift points seem to be the same so I don't detect frictional/viscosity effects of tranny fluid even after complete warmup. Today's engines have knock sensors that adjust spark advance (the more advance the better) to the point of detonation that is determined by octane level. You raise some interesting points but I honestly think it all boils down to fuel composition. Never had a vehicle that kept such accurate track of mileage. Would be interesting to hear from others. Thanks for your thoughts.

In the meantime, hope for spring.

[Amaury]

Iborer,

Whether is winter or summer or any other season, there are laws enforced by the government requiring that:

87 gasoline (regular) = 87% octane and 13% additives, including heptane
89 gasoline = 89% octane and 11% the other stuff
91 gasoline = 91% octane and 9% stuff….and so forth

The exception is the 10% ethanol that is now a mandate in many states, including my State, New York. Modern engine computers, however, adapt to the extra oxygen injected by the ethanol without sacrificing mpg. In the local level, your city’s Fire Department or Division of Weights and Measures conducts periodic inspections at randomly selected gas stations to makes sure that the gasoline you get at the pump is what you expect it to be. Exceptions do occur, since nothing is fool-proof but they are not wide spread.

About the tranny in your Avalon? In case you didn’t know and whether you notice it or not, your tranny cannot go past the third gear until the engine’s coolant temperature is equal to or greater than 117° F (there are other prohibitions as well that keep your tranny between the 1st – 3rd gears when the engine is cold). These are the gears which makes your engine consumes the most gas. Your tranny won’t even touch the overdrive gears (5th & 6th) until the coolant temperature is hot enough (~ 140° F) AND the transmission fluid temperature is equal to or greater than 32° F. These are the gears that save you the most gas.

These and the other factors I mentioned before are what make the needle in your tachometer shoots sky high when you first start your cold engine. In most instances, the higher that needle aims the more gas your engine is consuming. The normal idle speed of your Avy should be around 650 rpm. If you live in a cold state, it takes longer for that car to reach that idle speed in winter than in summer. All these translate into M-O-R-E G-A-S consumption during winter.


...and like yourself, can't wait 'til summer's here.

Amaury
’08 Limited

[lbroer]

Amaury,

Thanks for your reply. The 87 that you see on the pump does not necessarily mean that the fuel contains 87% iso-octane and the balance heptane. What it means is the fuel will give detonation characteristics equal to a 87% 13% heptane blend. What that means is that you could have a fuel composition that would give the same detonation (ping) characteristics at a less than 87% blend if the fuel contains an ignition improver that would provide equivalent ignition characteristics. In diesel fuel we call it a cetane improver. What this means to me is the fuel can be formulated for a variety of reasons and in that process it may contain fewer btus/gal but yet meet the 87 octane/knock specification. That is what tetraethyl lead was used for in the past and other additives are now used. Ethanol is a great ignition improver but it gives poorer gas mileage.

Secondly, I checked with the county guys here and the sticker they place on the pump only shows that you are truly getting the number of gallons showing on the pump. Testing the octane rating for gas and cetane rating for diesel is an expensive test. Local regulations might vary.

Your thoughta are welcome.

[lbroer]

Originally Posted by lbroer

Amaury,

Thanks for your reply. The 87 that you see on the pump does not necessarily mean that the fuel contains 87% iso-octane and the balance heptane. What it means is the fuel will give detonation characteristics equal to a 87% 13% heptane blend. What that means is that you could have a fuel composition that would give the same detonation (ping) characteristics at a less than 87% blend if the fuel contains an ignition improver that would provide equivalent ignition characteristics. In diesel fuel we call it a cetane improver. What this means to me is the fuel can be formulated for a variety of reasons and in that process it may contain fewer btus/gal but yet meet the 87 octane/knock specification. That is what tetraethyl lead was used for in the past and other additives are now used. Ethanol is a great ignition improver but it gives poorer gas mileage.

Secondly, I checked with the county guys here and the sticker they place on the pump only shows that you are truly getting the number of gallons showing on the pump. Testing the octane rating for gas and cetane rating for diesel is an expensive test. Local regulations might vary.

Your thoughta are welcome.

[CAPTMARK]

MINE drops a lot in the winter- think because I let it warm up for 20-30 min. each cold morning before I get in.

[Amaury]

Ibroer, my dear friend:

If diesel engines need an “improver” to aid ignition, gasoline engines definitely don’t needed. Did you forget diesel engines have no spark plugs? Their compression ratio is their igniter, so having an improver seems to make sense. Gasoline is far more volatile than diesel fuel, and then we combine it with spark plugs; who needs more fire for combustion? Don’t you know that by having different octane numbers we’re removing some of the volatility in the gasoline? Why, then, add more volatility later?

You shouldn’t have checked with the county guys; their answer to you reflects their knowledge.

The guys at the ASTM can give you all the information you may want on this topic. They’re the folks who set the standards for the octane rating of gasoline and other fuels. Since what comes out of your tailpipe depends on the composition of the fuel you buy, the federal government enforces ASTM’s regulation (are you familiar with the Clean Air Act?). This document also explains the reason behind using ethanol in the gasoline.

Analyzing gasoline for its octane number is rocket science; just as it is analyzing your breath for your blood alcohol content. In fact, the latter is more complex to analize. But somehow cops, who are not rocket scientists, can find out your BAC in seconds using a tiny, portable device called breathalyzer (starting price? $19.99). A similar device called Octane Analyzer can be used to measure gasoline’s octane level; expensive? Perhaps you could let me know.

Amaury
’08 Limited

(Could you explain in deep terms why ethanol is an ignition improver for gasoline engines and a failure in the mile-per-gallon department?)

[TrailDust]

I'm not aware of ethanol "improving" combustion, but then again I admit I'm not a chemical engineer. I suspect additives contained in the ethanol improve the quality of combustion, but not the ethanol specifically.

TrailDust