Does installing a Cold Air Intake increase or decrease gas mileage? I’ve heard answers both ways… I have a 2010 Toyota Tundra 5.7
For your particular truck, a cold air intake is not going to help much of anything but becoming addicted to the extra noise you will now hear. You’ll stomp the pedal more to hear the roar and you’ll lose MPG as a result. CAI for the most part are psychological. Very few regular street cars will make any use of the sales pitch promises.
What he said…the only benefit is if it (slightly) reduces the pressure drop in the intake at wide open throttle. At any other opening it’ll make about 0 difference to both mpgs and hp. But using wide open throttle definitely WILL lower mpgs.
I did a cold air intake on my Miata. Did it help? Possibly, but not significantly. When installing a cold air intake be careful not to have the intake too low in the engine compartment. If it sucks in water, you will hydrolock your engine. Not good.
Waste of money-Kevin
If it does increase fuel economy it probably won’t be measureable. If it increases performance…fuel economy will suffer.
The air filter on a typical CAI will let more dirt in than the OEM filter.
Many years ago such modifications were called “all show and no go.”
Unless you are going close to full throttle, a cold air intake will do little, and it’s mostly for show.
I’ll differ slightly from the mostly correct opinions of the others - depending on how your OEM air intake is designed, heat soak might be a problem - that’s when you sit at a stop light, underhood temperatures rise, and you suck in that warm air when you take off. Warm air is less dense than cold air, and so you lose power. so, a CAI will help there because it’s sucking in ambient-temperature air rather than hot underhood air.
That said, if you’re worried about drag racing at stoplights, your priorities are screwed up and you need to stop. 
Otherwise, they’re a waste, and are sometimes potentially damaging - some CAI’s go below the bumper, and if you drive through a puddle will suck up water and damage or destroy the engine.
Find where the current stock air intake is under the hood. Most are now located on the side of the motor near a wheel well. That is a pretty good place to get “cold” air. Would the location of your aftermarket air intake really be in a much better place to suck in cold air? Doubtful that it would be significantly different.
Most stock systems allow for some warmed air to be pulled into the airbox when the car is operated in a cold winter climate. This helps the car warm up smoothly. Your aftermarket setup might not allow for this. If you live in a cold climate you might find the car less driveable on cold mornings. You will spend money, get little to no benefit, and perhaps make your car worse.
The airflow is good from the factory; engines get plenty of it. There is also a system that warms the air so that the engine won’t stall when you take off. The warmer air also increases the fuel economy. The warm air system on the car gives a minimum of 50% warm air. It wouldn’t be on the car if it wasn’t a beneficial device.
Cold air is great when you’re burning nitromethane blends for all-out drag racing. There is no benefit from using colder air unless you’re getting that nitro fuel or you have a high heat racing problem which is preigniting the fuel.
Bottom line: There won’t be any fuel saving with a different intake system. Keep the one that was designed by the experts.
@pleasedodgevan2 No offense, but some of your information is flat out wrong. Cold air is denser than warm air, and therefore will result in a larger amount of fuel and air combusting per cycle, and therefore will increase power. Whether it will increase power much over stock is a question of how the stock intake was designed, but to say that there’s no benefit to having cooler air going into the engine is wrong - if you consider more horsepower a benefit, then there is absolutely a benefit, regardless of the type of fuel you use.
The only thing an aftermarket cold air intake will do for your truck is increase intake noise, a sound many people like, which will likely make you step on the gas pedal harder than before to hear the noise, which will decrease gas mileage. If your driving habits remain completely unchanged, your gas mileage will likely remain unchanged. All those cold air intake systems do is cost lots of money, look cool (if you think they look cool, anyway), and make more intake noise than the factory air box.
Turbos and super chargers benefit more from CAI than normal engines