Bad MPG

I have a 2000 Rodeo v6 @ 115K. My question is I calculated my MPG these couple weeks I have been getting only 14.3 MPG on city/highway. I notice that my thermostat temp is little bit lower than normal spec. People replace their thermostat because its overheating but it could also be under normal temp right? I live in Maryland and its getting colder and colder but I don't turn on my A/C heater at all.
I replaced my friend 97 Prizm thermostat couple weeks ago becuase it is under normal temp and after I changed the theromostat it gains 2 mpg!

I heard replacing thermostat for rodeo is kind of difficult, so I just want to make sure it might be one of the reason before I change it. I own this car since 68K@2004 and never replace it. I know bad gas mileage has many reasons and I changed fuel filter, air filter, oil filter, new tires, clean intake and so forth.

Thanks

Ken

I have 82k on my 2000 and I'm getting about 15mpg right now. it always goes down in the cold weather.

It may be worth your time to swap out the front 2 O2 sensors.

Under temp could be a problem, depends on how much. The ecu will richen the fuel mixture when the engine is cold kinda like a choke on carburated engines. A t'stat thats sticking open could cause it. They are not fun on 2nd gen rodeos. You have to remove the intake manifold to get to it.

With that said, thats about the same mileage I got on my last tank of gas. They switch to 10% ethonal gas here in november for winter gas which will kill gas mileage. If your area does the same thing that could be the problem and really nothing you can do about it. Mine usually drops 2-3 mpg from november to march while they make us use this crap.

yea Gizmo, all my areas use 10% ethonal gas. Thanks for help guys.
I feel like driving a hummer now!

Ken

Yep, my beast does it too. Drops from 19-20mpg city to easily 15-16mpg city winter temps, lucky for me I have a work truck now and am finding that the Rodeo sits for up to two weeks at a time. Like now, I haven't started it in 2.5 weeks....but I do not like to let it sit constantly like that, we'll make sure to drive it this weekend on our errands.

But, we're still paying gas price grunch on our Tacoma which too only gets 16-17mpg city in the winter, and it only has a 3rd of the mileage that the Rodeo does.

Also be absolute SURE if you do change your t-stat to use OEM Isuzu ONLY! All aftermarket t-stat's do not regulate this engine well and you do not want it to overheat.

I have a 2000 Rodeo v6 @ 115K. My question is I calculated my MPG these couple weeks I have been getting only 14.3 MPG on city/highway.

Wow, 14.3 seems awfully low, unless you've modified it quite a bit! It's hard to imagine a stuck-open thermostat could affect it that much, but perhaps. What had it been before?

My fuel milage stays at about 20.3 mpg year 'round on my 2001 with 95K miles, but it doesn't get very cold where I live. They add the EtOH in the summer here, rather than winter to oxygenate the high-smog season fuel. But it doesn't seem to make much difference in my milage. I calculate mpg on each tank, & I keep a running calc.

My fuel milage stays at about 20.3 mpg year 'round on my 2001 with 95K miles

I dont modified at all. wow, 20.3 mpg? you must drive on highway alot! I just feel that my temp gage drop little bit since its really cold here and it probably effect my mpg :banghead: . On the other hand, good sign that its going to snow soon. :naughty:

I find that using a "Fuel System Cleaner" added to the gas tank every few months does wonders for MPG in my 2001 Rodeo (110,000 miles.) Use the good stuff ($8/bottle) that cleans the whole system instead of the cheap $1.00 ones.

well i was getting 13 with a cold air intake took it off and got 15, put on manual hubs and its noticeably spunkier and better mpg i havent calcualted yet but its better for sure

Also remember to check your tire psi, it makes for a BIG improvement on these trucks.

I run my tires at 50psi all 4 corners.

For those with Passenger rated tires however, you can safely run 38-40psi all 4 corners without issue, and, in fact, it would probably aid in steering/handling too.