2018 5.7 Toyota Tundra. Mileage

Hi, does anyone know why I’m only getting 7-8 mpg with city driving, not towing. My last Tundra was an ‘08 with tow package and i was getting 15mpg in the city and highway. Both have the 5.7 motor, the ‘08 had 4.10 ring gear the ‘18 supposedly has a 4.30 on Toyota’ VIN info.

I can obviously tell that the ‘18 Tundra has a more highway gear ratio so not believing the 4.30 ring gear setup, I’m thinking more like a 3.90.

The local dealers are saying that it may be a catalytic converter issue.
Any thoughts would be extremely appreciated!

Go Tundra Nation!!!

 

How long have you had it and how many miles are on it?

 

Need more info. Mileage, service history and fuel trim data (via scan tool) would help. Is this a Flex fuel vehicle?

 

I’ve only had it for 4 wks, it has the same motor and approximate ring gear as my ‘08 which i owned for 17 yrs.
My ‘08 had 235,000 miles and got 15mpg city and hwy, the ‘18 has 112,000 and is only getting 7-8mpg both have the 5.7

 

Of all the possible things contributing to poor fuel economy like you describe, the axle gear ratio is very low on the list.

 

Mileage is at 112,000, the truck was a one owner vehicle with regular maintenance, I don’t know about the fuel trim data (scan tool) is this something that a certified Toyota shop can do? Not a dealer. A local dealer had mentioned that it could be a catalytic converter issue although i would think that the engine light would be on.

 

Hold up on the scan tool. Is this a Flex fuel vehicle? You’ll know if the fuel cap says E85 is okay and under the hood the engine code sticker will say “3UR-FBE” and your VIN will have a “W” in it.

 

Thanks for your help, no not a flex fuel vehicle.

 

Probably check tires, alignment and wheels.

 

Is this based on the dash read out or actual MPG calculated when filling up?

 

Tires and alignment are good, tire pressures are correct, Nitrogen filled. The truck does have upgraded 20” rims/ tires, Michelin street tires, vs the OEM 18” rims.

 

Yes, i had wondered this also, and checked with actual gallons per odometer readings. Thanks

 

Thank you for clarifying. 7-8 MPG is not normal. Could be a lot of things; final drive ratio will not cause fuel economy that poor.

You can get a scan tool that is able to read live data at Harbor Freight, Walmart, Auto parts stores, Amazon, etc. It will help pinpoint the problem. If I were in your position, I would verify that maintenance is up-to-date, particularly Air filter and spark plugs..."regular maintenance" to many owners means the oil was changed every 10,000 miles. If you can't verify from Toyota that the plugs have been changed, that's the first place I would start with a new air filter and fluids all around. Also, run a couple doses of Techron or other PEA-based fuel system cleaner to help clean up any dirty injectors.

If you service yourself, unplug the battery while you work on it to reset the fuel trims. Check fuel consumption MANUALLY (miles driven / fuel consumed). If still poor fuel economy, we can start pinpointing using live data.

Possible (more likely) causes beyond routine maintenance:
-Faulty Mass-airflow sensor
-Slow/faulty upstream O2 sensors
-Faulty/Dirty fuel injector(s)
-Faulty fuel pressure regulator
-Coolant temp sensor
-etc...etc.

Most of these are common repairs that come up after 100k miles.

A bad catalytic converter would throw a check engine light unless the downstream O2 sensors are bypassed or have spacers added to fool them.

 

one of the odd issues is the Toyota build sheet on the truck through Toyota’s VIN # check is that it is supposed to have a 4.30 gear ratio. My previous ‘08 Tundra with a 5.7 and the tow package, at 4.10 ratio had a lot more off the line response. I suspect that the build sheet is incorrect as the off the line response seams to be more inline with a 3.90 ratio. I have gotten ahold of the dealer that sold the truck but they are unable to see if the original buyer elected for a highway gear vs the towing gear ratio.

 

Are you more concerned about the final drive ratio or poor fuel economy? I can't help with the former; but the poor response and poor economy are very likely related.

 

Thanks WhiteSR5, I will look into this, obviously something is off on the vehicle. As mentioned my previous’08 was a total Bear on pulling and off the line response. If i selected the towing mode without a load, off the line this truck was crazy quick! The ‘18 Tundra with the supposed 4.30 gear’s are not close to being comparable and the 50% mpg loss is a total mystery.

 

Also maybe check if the butterfly valve for your air intake and oxygen sensor could be cleaned

 

The lack of quickness off the line is a separate thing. They changed the throttle input mapping because people complained about the earlier trucks being too jerky when you depressed the throttle.

 

Just bought mine. Here's my computer mpg. One way to work, 8 miles city stop and go.

 

8 in town is low. Most of my driving is highway and I see about 13.5 overall. Highway only is closer to 15. Towing my 25’ travel trailer gets me in the 8 range.

From my understanding, 4.30 was the only ratio available in 2018 4x4 models.

For comparison, my truck is also a 2018. CrewMax Platinum. She’s a fat pig, weighing 7,200# with me in it every day because of the canopy, heavy tires, and all the other shit that adds up. 285/75-18 LRE tires and 5.29 gearing.

Has your truck had its 100,000 mile service stuff done? Spark plugs, every fluid in the whole thing, clean air filter, belt, etc. if you’re not sure, now would be a great time to do it so you have a solid baseline.

 

A bad plug is possible, not sure if that throws a warning on whatever year OP has.
Used to get real shit mileage per gallon on a 5 cylinder Ranger until it was 6y cyl again.

 

That fuel economy is ungodly low. I have a 2018 5.7 and im on 37inch ATs and 4.30 axle ratio and I get around 10 in the city and 15 on the freeway. You should not be getting that low of gas milage stock.

First step is see if thats your actual milage. Drive to the gas station and fill up your truck. Then track every mile you drive (use gps to do this not your odometer in case its inaccurate). Once you are near empty fill up again and divide the distance you drove by how much you just filled up. This will be your ACTUAL MPG.

If this is still low then the issue wasnt your dash reading. I would start off by checking/replacing the engine air filter, do an oil change maybe using the correct viscosity oil, run an injector cleaner through your fuel system (like techron or seafoam, just make sure it has PEA), clean your mass airflow sensor, clean your throttle body, and check your spark plugs. Your plugs should not need replacing at 66k miles. They are iridium tips so they should last around 100k-120k. But check them still incase they are fowled with carbon. If they are fowled replace them and DEFINATELY run the injector cleaner once or even twice.

If the issues still persist then id replace the O2 sensors. I wouldn't worry about your axle ratio. 3.90 and 4.30 should not make a differnt in MPG of more than 1mpg unless you are towing, have oversized tires, live in mountainous areas, or have a lot of weight in the bed/cab.

Hopefully your cats are not the issue because that would be EXPENSIVE and these fuckers have 4 of them.

 

Stock weight is 5680! What you have is like fully loaded truck! I doubt mods add that much. You don't have any payload capacity left. How much do you weigh, sir?!

 

I’m 245#, but still sexy.

(5) 35” heavy tires
Heavier suspension parts with Deavers.
Alcon brakes are big and heavy
canopy
Bedslide
50L Dometic full of cold ones
Dual batteries
ARB dual motor air compressor
Stereo gear with a heavy sub box
200W Solar on canopy roof
A mid-size Action Packer tote with a few tools and minor safety stuff
Bunch of lights

It all adds up…. I’ve weighed it several times and it’s pretty much always in the 7,100 to 7,200 range. As mentioned, she’s a fat pig. And, you’re correct. I technically have no payload left. But, I’d argue that the heavier tires and wheels (4 of them), the big brakes, and half of the additional suspension weight ought not count against payload since they are unsprung weight that the truck is not carrying. This thread is not about that though, so let’s not discuss that theory here.

Back on topic, I just ran 340 miles on a hilly interstate in Western Oregon today. 75 mph with cruise, and rolled 13.9 mpg.

 

Another thing to consider, and I didn’t look back to see.

Is your speedometer accurate? When I went to bigger tires, I put in a Rough Country Speedo calibrator. It’s really close to perfect.

If you have larger tires without Speedo calibration, you’re not going to show as many miles per tank as you actually covered. Not by enough to show 8mpg on its own, but it all adds up.