Gas mileage huge drop ideas? - Toyota Tundra Forums : Tundra Solutions Forum
 
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post #1 of 12 (permalink) Old 04-21-2015, 05:42 AM Thread Starter
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Gas mileage huge drop ideas?

So, I have been tracking the gas mileage on my "new" 2005 Tundra double cab. for the first 1200 miles I had it, I was getting steady 16.3-18mpg. I drive almost entirely on paved country roads. However, this week, I noticed that my tank was down almost a quarter tank already, after filling up on Saturday. Just to check things, I filled the tank. 4.93 Gallons for 53 miles....only 10.7MPG. I mean, lowish MPG, in the 12-13 range is expected, but this is way low.

Some factors:
New tires
It got colder by about 40 degrees
I idled the truck for 15 minutes yesterday to warm it up since I was dropping the baby at daycare.

Those are the only differences from the previous driving. What could have caused that huge drop? Is there anything I should be looking at? Or do I see how it gets for economy this tank and go from there?

buddy: My wife still giggles when she sees it
Me: That's ok, I giggle when I see Priuses too, but that's different


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post #2 of 12 (permalink) Old 04-21-2015, 06:05 AM
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Re: Gas mileage huge drop ideas?

Off the top:
  • What size were the previous tires and what size are the current tires?
  • Cold definitely a factor
  • Are you sure you topped off the tank? I have filled up a few times only later to discover that I was a few gallons short when the pump shut off.
  • Are there any CEL codes?
I would drive it for a few tanks and monitor the mileage. It is entirely plausible that you got a bad batch of gas. If the bad mileage continues then you need to start looking to a few things.

In the interim I would clean the Throttle Body and the MAF sensor. Do you have any dragging brakes? It may be possible that you have a catalytic converter on the way out. I once a had cat burn out and my mileage took a massive dump - very similar to your drop but it did not throw a code for about 100 miles or so.

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2004 Tundra Double Cab Limited Edition 4.7 liter V8, four speed automatic, four wheel drive, testing platform for fuel economy, Ultragauge, Long Tubes with x-pipe and true duals,stock intake, Mobile 1 in the engine, NAPA oil filter, NAPA [COLOR=Black]in the differentials. 3:91 gears in the front and rear [SIZE=2]differentials, Cooper Discover ATP tires


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post #3 of 12 (permalink) Old 04-21-2015, 06:15 AM Thread Starter
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Re: Gas mileage huge drop ideas?

new tires are the same size as the old ones, only difference is tread and load rating, 110 versus 112. Both sets of tires were standard, not LT tires. NO CEL codes. Not filling all the way may be a culprit from the previous filling. I'll plan on driving it for a few more tanks and see how it goes. I just kind of freaked out, since I only bought the truck less than a month ago, and have only 1200 miles on it myself. The drop was huge

Edit: well, pretty much ruled out the new tires as a cause....I drove 63 miles home after getting them installed. To keep the 17.8 MPG I averaged on that tank, I'd have to have gotten 22 MPG for the other 193 miles I had on that tank (filled at just under half)....

so I'm thinking, with the drop in temp from the 60s-70s on the previous days to the 20s-30s yesterday and today, combined with idling for 15 minutes yesterday, and just sucky windy conditions, my 10 year old truck just got cranky

buddy: My wife still giggles when she sees it
Me: That's ok, I giggle when I see Priuses too, but that's different


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post #4 of 12 (permalink) Old 04-21-2015, 10:12 AM
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Re: Gas mileage huge drop ideas?

Just spitballing here but another possibility is a leaking injector or a vacuum leak.
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post #5 of 12 (permalink) Old 04-21-2015, 10:15 AM Thread Starter
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Re: Gas mileage huge drop ideas?

Quote:
Originally Posted by SalahHH83 View Post
Just spitballing here but another possibility is a leaking injector or a vacuum leak.
Thanks. another thing to keep in mind.

I know this was only a partial tank, so I'm going to see if the problem persists. I'm going into town today....50 mile round trip, this ought to give me more of an idea, I'm going to keep monitoring this week and see after I have over 100 liles on this tank.

buddy: My wife still giggles when she sees it
Me: That's ok, I giggle when I see Priuses too, but that's different


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post #6 of 12 (permalink) Old 04-21-2015, 12:20 PM
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Re: Gas mileage huge drop ideas?

Best bet would be to track your mileage and look for a trend. Get a GPS and verify that your odometer is measuring correctly.

The only 'real' way to track fuel mileage is to get an accurate distance, and number of gallons. Every pump will shut off at different fill levels. The way to do it would be to 'top it off', until you can see the gas in the filler neck. This is not recommended by many, since it may back up into the vent system, leading to more issues.

This is why I recommend looking at a trend, some times you may fill it a little closer to full, other times you may be a little less, but over a few tanks, you should be pretty close. I have a spreadsheet that I use, and I graph the mpg. This just makes it easier to see what I am getting, and it also makes it very easy to see if I am going up or down in mpg.

I typically only fill up when the tank gets below 1/4, as opposed to filling with only a few gallons, this way, if you did get a bad tank of gas, you won't keep diluting it, and extending the poor performance.

Then if you want to be scientific, do a maintenance procedure, or a modification, and run a few tanks through. Do only one thing at a time, and you will see the results - good or bad. If you don't care, or don't have the time or patience, do what you think you need to do all at once.

How many miles are on the truck? Do you know what the maintenance records look like? As mentioned above, a throttle body cleaning, and MAF cleaning may be a good place to start. Plugs may be next, if you don't know the history (I recommend factory plugs, or equivalent). Air pressure in the tires should be checked.

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post #7 of 12 (permalink) Old 04-21-2015, 12:33 PM Thread Starter
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Re: Gas mileage huge drop ideas?

Quote:
Originally Posted by asc08 View Post
Best bet would be to track your mileage and look for a trend. Get a GPS and verify that your odometer is measuring correctly.

The only 'real' way to track fuel mileage is to get an accurate distance, and number of gallons. Every pump will shut off at different fill levels. The way to do it would be to 'top it off', until you can see the gas in the filler neck. This is not recommended by many, since it may back up into the vent system, leading to more issues.

This is why I recommend looking at a trend, some times you may fill it a little closer to full, other times you may be a little less, but over a few tanks, you should be pretty close. I have a spreadsheet that I use, and I graph the mpg. This just makes it easier to see what I am getting, and it also makes it very easy to see if I am going up or down in mpg.

Then if you want to be scientific, do a maintenance procedure, or a modification, and run a few tanks through. Do only one thing at a time, and you will see the results - good or bad. If you don't care, or don't have the time or patience, do what you think you need to do all at once.

How many miles are on the truck? Do you know what the maintenance records look like? As mentioned above, a throttle body cleaning, and MAF cleaning may be a good place to start. Plugs may be next, if you don't know the history (I recommend factory plugs, or equivalent). Air pressure in the tires should be checked.
105, 739 miles on the truck. I've been tracking using the same pump for the last 1200 miles, which is the whole time I've owned it. Before this last little fill up, it was getting 17 MPG average. Tires are brand new, P tires at 35psi front and back. not sure on maintenance history other than what I found n the Toyota site which is pretty generic. Last oil change was about 2000 miles ago, planning to clean the throttle body when the weather clears up too. planning on running another 2-3 tanks through it before doing anything, to see how it goes. between today and tomorrow, I have another 100 miles I'll be putting on between tonight and tomorrow, so that should tell me something.

I was just surprised at the pretty major drop in mileage that I seemed to get on this time......more tracking will continue to get a better idea

buddy: My wife still giggles when she sees it
Me: That's ok, I giggle when I see Priuses too, but that's different


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post #8 of 12 (permalink) Old 04-22-2015, 12:08 AM
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Re: Gas mileage huge drop ideas?

Quote:
Originally Posted by MNFinn View Post
Just to check things, I filled the tank. 4.93 Gallons for 53 miles....only 10.7MPG. I mean, lowish MPG, in the 12-13 range is expected, but this is way low.
Your gas mileage hasn't changed. The reason for the apparently low mileage is the short fill.

I've noticed this on my truck. Top off the tank with a few gallons and the calculated gas mileage is always low.

Part of the reason is that a 1 gallon variation in fill to automatic shut-off is 5% of a 20 gallon fill but 20% of a 5 gallon fill. Yet there's more to it than that I think I'm but not really sure what.
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post #9 of 12 (permalink) Old 04-22-2015, 04:42 AM Thread Starter
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Re: Gas mileage huge drop ideas?

didn't think about that. That's good info to know

buddy: My wife still giggles when she sees it
Me: That's ok, I giggle when I see Priuses too, but that's different


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post #10 of 12 (permalink) Old 04-22-2015, 05:15 AM
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Re: Gas mileage huge drop ideas?

Quote:
Originally Posted by mibro View Post
Your gas mileage hasn't changed. The reason for the apparently low mileage is the short fill.

I've noticed this on my truck. Top off the tank with a few gallons and the calculated gas mileage is always low.

Part of the reason is that a 1 gallon variation in fill to automatic shut-off is 5% of a 20 gallon fill but 20% of a 5 gallon fill. Yet there's more to it than that I think I'm but not really sure what.
Absolutely correct - how did I miss this. Attempted points but the powers that be denied me.

355,164 miles on the odometer [come see me when you get that on your ford]



2004 Tundra Double Cab Limited Edition 4.7 liter V8, four speed automatic, four wheel drive, testing platform for fuel economy, Ultragauge, Long Tubes with x-pipe and true duals,stock intake, Mobile 1 in the engine, NAPA oil filter, NAPA [COLOR=Black]in the differentials. 3:91 gears in the front and rear [SIZE=2]differentials, Cooper Discover ATP tires


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post #11 of 12 (permalink) Old 04-22-2015, 06:16 AM
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Re: Gas mileage huge drop ideas?

also, you'll notice that the 1/4 tank increments don't drain equally. my first half tank = 200 miles. the second half tank gets me puckering at about 100 miles which leaves me between 4-5 gallons at the E, but not empty.

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post #12 of 12 (permalink) Old 09-18-2015, 07:29 AM
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Re: Gas mileage huge drop ideas?

I like the idea about the fill-ups being different even from the same pumps. I too, have experienced the reduction in mileage recently. I wouldn't think the temperature drop recently from the 90's to the 80's would have an effect on this but... I just cleaned the throttle body and it appears to have dropped my mileage from around 15+ to 13. I have an '04 double cab with 102K, new timing belt and kit (Aisin). I put in plugs a couple summers ago (NGK) and probably need to change them out. Don't think I left off any vacuum hoses but will check. Keep the info coming. I can use any help you guys can provide. The only positive is the drop in fuel prices. Down to $2.07 here.
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