FAQ - My gas mileage sucks
Every Jeep owner asks himself this question - "What do I have to do to get better gas milage?" Soon afterwards the question shows up on JeepForum. This usually happens in the winter-time. So - I figure its time to create a FAQ on why gas milage sucks worse in the winter than in the summer.
First things first, I will assume that your vehicle is tuned up with good spark-plugs, clean filters (air, fuel, oil) and that all the fluids are changed at the recommended intervals.
Second, I will assume that the air-pressure in the tires is at the recommended PSI and that the tires are rotated regularly (not by vehicle power, but, actually removing the tires and putting them on different axle-ends).
Now, we will get to the meat-n-potatoes of the question and what you can do to get either better gas milage or possibly just make it suck less.
Remove all excess weight from the Jeep. Do you need to carry that dead-weight of a winch all the time on the front? Do you need that dead-weight in the back of ropes, chains, axes, hi-lift, spare-tire, tools, fluids, back-seat, etc. Is it better to try to improve your aerodynamics by removing the huge rack over the roof when you don't need it there? Do you need the ski-rack on the top all week when you only go out for the weekend?
Will a CAI improve your milage? Will a snorkle improve your milage? Will any bolt-on "power improving" gadget improve your milage?
The answer is "not really" or "not significantly". Over the long-term you might gain a few miles or kilometers per tank in a highway driving situation, but, for standard city / in-town driving there really isn't any significant improvement due to factors beyond your control. Street-lights on every corner stopping you, idle-time, traffic-flows during rush-hour, etc. Whatever gains that you might receive from the gadgets would be negated by those kinds of circumstances.
If you are a coastal driver, you have the "thickest" air. Adding any goodies to try to improve milage won't do you an ounce of good. If you are a mountain-driver, you will have the thinner air. Anything that you can do to force more air into your Jeep will help - a bit. When my Jeep is around the coast, I have had ~600km/tank. When my Jeep spends its time at higher altitude (my normal region), my gas milage drops to ~400km/tank. This shows what kind of effect the different areas have to an engine.
If your Jeep came with the 3.07:1 gear ratio, you are running the best gear ratio for highway. It will be a little harder for you to get off the line, but, your RPMs will be lower - saving you gas, but there is a greater chance of stalling out on the trails.
If your Jeep came with the 3.73:1 gear ratio, you are running a decent ratio for street / trail use - neither will shine - neither is very detrimental to driving.
If your Jeep has 4.10:1 gears (non-4-cyl) -> 4.88:1 (or further) then you are raising your RPMs (and fuel-usage) at highway speeds, but, it also gives you greater off-road ability.
Finally - lets get to the weather-factor that ruins gas-milage.
When the temperature starts to drop below freezing all the fluids in the Jeep slowly turn into a gel. You can experiment with this at home. Take equal amounts of engine-oil, transmission oil and gear oil and split them up.
One container of each will be kept at room temperature.
One container of each will be placed in the fridge over-night.
One container of each will be placed in the deep-freeze.
Gather up some containers to catch the fluids and set them out. With a friend (or more) take one batch of similar fluid (lets say engine oil) and try to pour them all out - start at the same time and the container that empties first is the winner.
Repeat with the other fluids.
What you will find is that the warmer the fluid is, the easier it will be to pour. Consider this fact when you think of the metal parts in the Jeep trying to move through the fluid. Your engine needs to work much harder just to get the metal moving through the fluids - then try to get the Jeep moving as well.
Finally - cold-air is dense air. Meaning that the colder it is, the "thicker" the air is. When it reaches the engine, the heat will expand the air. You are then "pumping more air in" than the thinner summer air. This is significant due to more air in = more gas used. The fuel-injection-system recognizes the air-to-fuel ratio and adjusts as required. The CO2 sensor in the exhaust tells the computer that there is more air or more fuel or more un-burned fuel or ... and compensates to a factory-set "perfect ratio".
I am sorry - but - with all the factors working against us, getting better gas-milage is difficult at best. There are little things that you can do - lower your speed, change fluids and filters regularly and remove any excess weight.
Hello, my name is Vance and I am a Jeepaholic.
Its better to be naked with your friends, than to be clothed with your enemies
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