Loss of 20% Fuel Efficiency after Service

[arharroz]

My Land Cruiser was running great with some minor issues. I had service (outlined below) and now have loss 20% of my fuel economy. I haven't been given a satisfactory answer by any of the dealership or mechanics, so I was hoping someone could help.
I'll be brief by using bullet points about the vehicle and recent service. If someone needs more info, I'll be happy to supply.

VEHICLE INFO:

• Year: 1998
• Current Miles: 212k

RECENT SERVICE:

• JULY
  • Replace Radiator
• September/November
  • Replace O2 sensor
  • Inner Tie rod
  • New tires

 

[oakback]

What are your before/after MPGs? Also check your tire pressure, especially since colder weather drops PSI.

 

[arharroz]

I went from 15 to 12.5.

I still think my tires are my issue. Hibdon replaced the tires with the same size, but a completely different tire. I am currently trying to get them to find a replacement tire for me.

 

[KC100series]

What part of the country are you in? Assuming Norman, OK? Could be the switch to winter blend fuel causing some if not all of your MPG drop

 

[arharroz]

That was my dealer's thought at first. I had this problem a month ago though. Could it really be a big coincidence to produce that big of a drop? I don't recall this kind of drop during past winters.

 

[planomateo]

Yup, like others, I would bet winter blend is hurting your numbers.

 

[abuck99]

Did you happen to increase the tire size?

 

[94SRUNNER]

He stated no change in tire size, if I read his post above correctly. I'd find it hard to believe that a different model tire in the same size would result in a 20% reduction in mileage. Maybe a few percent.

 

[planomateo]

What brand/type tires were you running before and what are you running now?

 

[bctlex]

Maybe the one of the caliper is stuck?

 

[rusty_tlc]

The mechanic disconnected the battery to do the radiator change, the ECU lost memory. Give the ECU a week or so to relearn the engine then recheck your mileage.

Just guessing here, but I seem to recall a similar thread a couple of years ago.

 

[arharroz]

Maybe the one of the caliper is stuck?

That actually isn't a bad diagnosis. I felt it dragging this morning.

 

[arharroz]

The mechanic disconnected the battery to do the radiator change, the ECU lost memory. Give the ECU a week or so to relearn the engine then recheck your mileage.

Just guessing here, but I seem to recall a similar thread a couple of years ago.

Ok, it was over a month ago, but I will be patient with it.

 

[KCJohnson]

I would check O2 sensor. You may be burning richer causing MPG drop.
Does it seem to run better than before?

 

[ponytl]

since we are playing bingo here I'm going to say.... when they replaced the tie rod they now have affected the toe OUT it is rare you can feel "MINOR TOE OUT" as the car/truck will ride and drive fine... but a few degrees of toe out will increase drag/scuff by a huge amount... slight toe in static (at rest not moving) can put you at Zero while you are moving... zero is great for speed and mileage ... but is a bitch to drive... it will dart and dive like a drunk hummingbird in flight... on super speedway cars we wanted all 4 wheels as close to zero under load (power and downforce) as you could get... horrible to drive but fast
if there was one thing they did that could kill mileage... it would be to get the toe out off by a few extra degrees, that could be equal to dragging a parachute that would only get bigger as you went faster... the fact that you have 200k+ miles means you have some worn parts/bushings that could/would even exaggerate it more... so they MIGHT have aligned it to specs, BUT it's adding to the toe out under load... I do this setting myself (another post) because I know the feeling I want and I creep up on it... since most of my driving is 30-40 mile trips on the local highway @ 60-70mph thats what I adjust it for...

 

[Sandroad]

In Tire Rack testing, they usually find differences in rolling resistance in tires that shows up in mpg differences, but it's never as much as 20%. Usually more like 1%-3%. That could be part of the problem, but only if the new ones were especially poor in rolling resistance. Winter gas could be part off the problem too, but again, not the entire 20%. However, if the shop messed up the 02 sensor with either the wrong one or something else wrong with that, it could also affect mpg and maybe a lot. Was just one sensor replaced? It seems like you'd get a CEL if something were way off with the 02 sensors, but I would double check that and maybe replace the other upstream sensor before blaming it all on the tires.

 

[JayM]

is it possible the bad sensor had truck running lean =better mpg? +heavier tires and winter fuel?

 

[JayM]

also The ecu was likely reset so you would likely be running less efficiently until your ecu re learns your driving characteristics. Add it all up and it would be probable to loose that much mpg.

 

[TXLX100]

Likely a combination of new 1 new O2 sensor, winter fuel, tires or tire pressure. Air your tires to 40psi and take a long highway ride at 65mph and measure mpg with map mpgs. Dealer should be able to read the fuel trim and differences in the heater sensors, if there is any indication there. My lx with 285 tires gets about 12-13 in the city, 15 on the highway if we keep it under 70

 

[LXPearl]

My first impression is the change of tires would be the primary culprit. When I changed the OEM LTX S rated original tires to the H rated LTX (designed for LC/LX), I saw a drop of about 1 mpg hwy. I preferred the ride and handling of the H rated LTX, so have stuck with them. I get 12 city and 14.5 hwy. That difference is with the OEM Michelin LTX M/S (275/70-16) and only between the S or H rating. Going to a different brand and tread pattern can easily have notable differences of 1-2 mpg.