Gas Mileage dropped like a rock

Clemsonfan15

Clemsonfan15

New member
So I fill up my gas tank sometime last week and this time I add Marvel Magic to the gas. I heard about this stuff from a guy at Lowe's and figured I would try it, so I did. This stuff worked great. I got 150 miles to a half tank, but after that my mileage dropped.

After I got to a half tank I performed the deckplate mod and added a K&N air filter. I thought that these two upgrades should get me better gas milage, but boy I was wrong.

I kept my driving style the same, so I decided that was not the cause.

I'm really confused. What caused my gas mileage to drop so much. 150 miles to the first half tank, but then 90 miles to the second half tank AFTER the upgrades.

I need ya'lls help.


Edit: I just got home from filling it up and it was like 17.2 mpg. This is like a 1 mpg gain. I was honestly expecting more.
 
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Could be any number of things. Most likely the ECU hasn't compensated for the new mods.

However, ideally, you should have run a full tank through it and then done the mods on a new tank of gas. Also keep in mind that the gas gauge isn't terribly accurate within a single tank of gas (especially if you have the very common inaccurate gas gauge problem). It is best to run a full tank through, then fill up and divide the miles traveled on the last tank by however many gallons you just put in. Always fill up the same way, and you should get a pretty accurate idea of what your MPG's are.

Making milage guesses based on the fuel gauge during one tank of gas is not going to give you any meaningful data.
 
CO_FlyFisher said:
Could be any number of things. Most likely the ECU hasn't compensated for the new mods.

However, ideally, you should have run a full tank through it and then done the mods on a new tank of gas. Also keep in mind that the gas gauge isn't terribly accurate within a single tank of gas (especially if you have the very common inaccurate gas gauge problem). It is best to run a full tank through, then fill up and divide the miles traveled on the last tank by however many gallons you just put in. Always fill up the same way, and you should get a pretty accurate idea of what your MPG's are.

Making milage guesses based on the fuel gauge during one tank of gas is not going to give you any meaningful data.
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It's just weird that I was getting like 240ish before the mods and I'm still getting 240ish after.
 
Also the problem to begin with is those mods have proven gas mileage increases be minimal or even negligible at best.

When the last time you had a real tune up? I'm guessing you might see another 1mpg but the fact is most (even well running or even new 3rd gens) get 17-18 in the city and 22ish on the highway and there really isn't a magic mod or something you can add to the oil to make solid and consistent MPG gains.

My miles per tank is anywhere from 230-250 with mostly city driving and I have a deckplate and K&N.
 
RonMAIDEN said:
Also the problem to begin with is those mods have proven gas mileage increases be minimal or even negligible at best.

When the last time you had a real tune up? I'm guessing you might see another 1mpg but the fact is most (even well running or even new 3rd gens) get 17-18 in the city and 22ish on the highway and there really isn't a magic mod or something you can add to the oil to make solid and consistent MPG gains.

My miles per tank is anywhere from 230-250 with mostly city driving and I have a deckplate and K&N.
Click to expand...

Ok. Thanks. I guess I was just wishing to achieve too much. The fact that they really don't improve gas mileage is correct. I'm not really sure why I overlooked that.

I suppose I just wanted a little too much out of the car. 20 mpg would be sweet. :).
 
I would be happy if I got 240 to a tank. I never pay attention to it but I think I'm aroud 15 mpg. Maybe 17. And that mostly city. But I do offroad a few times a week and that kills it. I have used 4wd high in the snow and got as bad as 180 miles right after I somehow squeezed 18 gallons in. Ugh!
 
I am only getting about 126 from 3 quarters down to below a quarter of a tank. Idk what my problem is.
 
Wow. Old thread. I'm not using Marvel Magic anymore.

I'm getting around 17.2-17.7 with all city driving.

I went out to my 4runner today and discovered that I have the stock spark plugs, wires, and I believe fuel filter. I think if I changed these my MPG would go up.
 
Im not sure what the situation is but I might have an answer for your change in mpgs between the first half and the second half of your tank. There was actually no difference between the 2. The way a gas gauge works is that there is a little sponge like thing that sits in your tank with a cable attached to one end. As the fuel in your tank lowers the sponge lowers and pulls on the cable. If you remember my thread about tightening the throttle cable at the throttle body, the reason why it needs tightening is because over time the cable stretches. The same thing kind of applies to the fuel gauge. So the first half of your tank will drop rather slowly compared to the second half because there's more strain being put on the cable when its lower in the gas tank. If you notice, true empty is actually almost 1/8 below the empty line on your gauge. This is also caused by the strain. So technically when your gauge shows 1/2 at tank you're actually at about 5/8 of a tank cause just like the gauge drops faster from 1/2 tank to empty the opposite happens from full to 1/2 a tank.

So moral of the story is, never trust your fuel gauge.
 
I'm only getting about 12-14 mpg with my 3RZ which is a disappointment. I think I need to replace my fuel filter though, I'm not really an aggressive driver.

I feel your pain clem...
 
where is there a "city" in NC? hahah.

I keep thinking of NYC or SF/LA when I hear city.

I just drove through SF in traffic and watched my needle drop and drop and drop:(

I'd do anything to get better gas mileage.
 
I'm in SC auctually. I guess my city driving isn't equal to yours. I'd hate to live in NYC or LA or any big city for that matter.
 
clem,

i noticed after i used sea foam that whole tank with it in it sucked got absolute crap lousy mileage.
 
haha idk maybe cleaned up some things internally but i didnt have a whoa!!! factor. im gonna do a more thorough system cleaning by my shop.
 
ive done all of that except the fuel filter which prolly needs it. damn wires were $$ 70 bucks! no im not frugal but for 3 wires give me a break!
 
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