Sudden Increase in MPG after being taken to glass shop for repair?? (Did they abuse it?)

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DougieLX470

Joined
Nov 16, 2021
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Hey Everyone!

This has been bothering me for a while so wanted to get it off my chest and see what you guys think. Maybe a month ago I got a check engine on for P0446 which is an evap issue. I took it to the dealership and they let me know I need a new fuel canister. The check engine light is on but they said it would be okay to drive in the short term until I could source the part.

Anyways, the next week I took it into a glass shop to have some cracks on the windshield sealed. At this point in time, the fuel economy was a bit higher than usual (which is expected with this issue) at approx 22L/100 KM. At the end of the day, I picked it up and saw it was at 30L/100 KM!! A huge % increase. I tried asking the front desk about it but they were adamant that they only drove it into the shop from the parking lot and back to the parking lot.

FYI I've never seen it this high.

Over the past 2 weeks, it has since gone back down to 23L/100 KM. Unfortunately, I don't have a dashcam so I don't know what actually happened but is it possible that the fuel economy could have just randomly jumped like that in a day? Or did someone at the shop ride it hard on a joyride? If its the joyride - should I be looking out for anything? They must've ridden it pretty hard to get it to that number - this has gotten me pretty worried.

Let me know your throughts. Thanks in advance!
 
Last edited:
If they disconnected the battery when changing out the windshield then that may reset the system, causing any short drive they may have taken after to show a heavy L/km. Could also be if they let the cruiser sit and idle any.

I wouldn't be too worried.
 
Agreed. It's pretty likely it idled for a while; they could have had vehicles to jockey around and let a few sit during that process. If it wasn't driven for any real amount of time after this, it would show the consumption as being pretty high.
 
They took it on a joy ride...for sure...

1651005126283.png
 
yes, the puzzling thing about it is that when they gave it air, you knowm jumping woopdedoos at high speed and flooring it while flying, it would not take that much juice to get the engine to 10,000 rpm and the wheels to follow, so why would the mileage be worse? Very strange...
 
Joyriding a 100 series that goes 0-60 in like 22 seconds :) I think that you have nothing to worry about, they maybe disconnected the battery. Don't sweat it :)
 
e9999 said:
yes, the puzzling thing about it is that when their gave it air, you know jumping woopdedoos at high speed and flooring it while flying, it would not take that much juice to get the engine to 10,000 rpm and the wheels to follow, so why would the mileage be worse? Very strange...
Click to expand...
Haven't you seen Ferris Bueller's Day Off? They had to drive it backwards afterwards to take the miles back off the odometer.
 
indeed, and the good thing is that if you lift it up on jacks to go backwards (you need two, right, or else you could end up going backwards through a door or somethin'), you can run it at 10,000 rpm the whole time... Even better! Music to a true TLC aficionado's ears...!

but anyway, back to Tech, did you fill the tank since then for the comp to reset the l/km and restart fresh?

(btw, a minor semantics point but we Mudders are annoying like that: increasing the mpg is a good thing!)
 
I don't think that the shop would've disconnected the battery as they were just filling cracks in the windshield and not actually removing it. It took about another 100 KM or more of driving to get the fuel economy back down - which is the only reason I was concerned. If it was just idling for a short time, it wouldn't have taken so long to get it back down right?

@e9999 I have not filled the tank to reset it but I'll give it a go this week and see where its at.

Thanks for all the good humor everyone! :)
 
DougieLX470 said:
it. It took about another 100 KM or more of driving to get the fuel economy back down - which is the only reason I was concerned. If it was just idling for a short time, it wouldn't have taken so long to get it back down right?

Thanks for all the good humor everyone! :)
Click to expand...

It would have been the same if they were out joy riding it. Average is average.

Maybe I missed it- what was the mileage immediately before and after the service?
 
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MongooseGA said:
It would have been the same if they were out joy riding it. Average is average.

Maybe I missed it- what was the mileage immediately before and after the service?
Click to expand...
I wasn't able to get the actual mileage (I didn't check it before I dropped it off). I only have the fuel economy to go off of. 22>30.
 
DougieLX470 said:
Hey Everyone!

This has been bothering me for a while so wanted to get it off my chest and see what you guys think. Maybe a month ago I got a check engine on for P0446 which is an evap issue. I took it to the dealership and they let me know I need a new fuel canister. The check engine light is on but they said it would be okay to drive in the short term until I could source the part.

Anyways, the next week I took it into a glass shop to have some cracks on the windshield sealed. At this point in time, the fuel economy was a bit higher than usual (which is expected with this issue) at approx 22L/100 KM. At the end of the day, I picked it up and saw it was at 30L/100 KM!! A huge % increase. I tried asking the front desk about it but they were adamant that they only drove it into the shop from the parking lot and back to the parking lot.

FYI I've never seen it this high.

Over the past 2 weeks, it has since gone back down to 23L/100 KM. Unfortunately, I don't have a dashcam so I don't know what actually happened but is it possible that the fuel economy could have just randomly jumped like that in a day? Or did someone at the shop ride it hard on a joyride? If its the joyride - should I be looking out for anything? They must've ridden it pretty hard to get it to that number - this has gotten me pretty worried.

Let me know your throughts. Thanks in advance
Click to expand...
DougieLX470 said:
Worn out gasket of the fuel tank cap can also cause P0446. Fuel canister rarely clogs up unless you are filling your car's fuel tank to the brim every time you refuel your car. Last year my car also throw the code P0446 but after replacing fuel tank cap the fault code went away by itself. Maybe the fuel is evaporating from your fuel tank that is causing decrease in fuel economy.
Click to expand...
 
The new evap cannister will increase your fuel economy for sure.
A friend with a V8 4Runner went from 19L/100km back to 14L/100KM just by replacing the damaged/full of fuel cannister. Good $1000 after I kept telling him not to overfill his gas tank.
Back to your topic. The shop most likely left the vehicle idling for a while and definitely took it for a ride inspecting for wind noises at high speeds.
Should you be worried? No
Did they do their job properly? Yes

I used to run production in a well respected body shop and took many vehicles on test drives to detect rattles or noises. Either you can go for a longish drive along the highway or floor it to get up to speed in a street that you know.
Unfortunately is all about efficiency and managers don't like guys going on the road for a long time or risking that something will happen.

Don't worry about it
 
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