Gas mileage drop after repairs

gasoline
jaguar
x-type
fuel-economy

#1

I bought a used car last summer, and so far it’s been great. I drive a great deal (about 40,000 miles a year, all rural highway driving) and so the selling point for me was that a)it was AWD and b) that it got around 24 mpg on the highway.



In the the first four months or so of driving it, I was averaging 24-25 mpg over a tank of gas, and even higher on trips that didn’t involve going over mountains.



And then my dad borrowed it for a couple of weeks and it became a victim of the frequent rockslides on the road over which he commutes. It was covered by insurance, but the long story short was that it got a new radiator, a new (rebuilt) transmission.



Three months after the accident, I finally got my car back. However, now the best gas mileage I can get out of it is 20-21, and with gas prices rising the way they have, and the miles I put on this car… well, it adds up and I’m kind of vexed by the whole thing.



What could have caused the drop? How can I fix it?


#2

You’re going to need to say more about what happened in the accident and what was involved in the repairs. A new radiator, for example, makes sense. A replacement transmission does not.

That said, the cooling system is crucial to gas mileage as is the alignment. Both of those things were likely affected but you need to say more if you want better guesses.

Presumably you have checked the pressure in the tires?


#3

If the 24-25 mpg was in the warmer months, then 20-21 mpg in the winter is not too far out of line. My vehicles’ mpg drops around 10% in the winter. Have you checked the tire pressure recently?

Ed B.


#4

A detailed list of what was repaired would help. For example if there was possible frame damage, and it was not carefully checked to make sure it was not bent and was properly adjusted, that could well be the problem.

I would start by making sure I was measuring the before and after mileage exactly the same way and that it is an accurate method of measuring mileage.


#5

Of the “links” that we see I find the “after such and such repair the mpg of record has dropped quite a bit” type a bit hard to pin down, I would first suggest that you check if the new mpg falls out of both what the EPA rated the car at and then what independant testers stated they actually observed the car get (I realize the independant observable figure may be hard to find). After looking these figures over get the car up and see if you can detect a wheel dragging. I did once find a wheel dragging but what led me to the “find” was not a search for poor mpg but it was a request from the customer for a “wheels off” brake inspection. I never would have found the dragging brake as the pad dragging was on the inside and not visible when doing a “through the wheel inspection”. The vehicle was a 2001 BMW X5 and the pad was so worn that there was metal to metal contact.


#6

Yes, the tire pressure is fine. The thing about the winter thing is that of late, we’ve been having unseasonably warm weather (comparable to April) and I live in the mountains, so it was winter-cold in November, when the car was in the accident. Though I suppose the gas is different in the winter, too.


#7

My dad hit a large, pyramid-shaped rock in the middle of the road. It crumbled the valance, and punctured the radiator and the oil pan cooler. It was hemorrhaging coolant and transmission fluid. They originally just replaced the oil pan cooler and things related to that, but it seems that in moving it off the road, damage was done to the transmission itself, though they didn’t know that until they’d replaced everything else. After they fixed everything else, but before they realized that the actual transmission itself was bad, they sent it in for a full alignment.

I’ve attached a picture the repairs list the insurance company sent me.


#8

Hmm…well, while we were having all the work done, we replaced all the brake pads. The EPA mileage is 16/23 mpg, at least according to edmunds, but I could swear that I saw it listed as 18/24 in all my original research, and a quick google search agrees.

In any case, it seems weird that it should remain on the low side of things, considering the driving I’m doing. Hell, the reason I’m really worrying is that I’m getting very close to the same gas mileage as my old car on these drives (a 1991 ford explorer, which I ended up driving again while my new car was in the shop), and half the reason I bought this car rather than another SUV was that the savings in gas would pay for a great deal of my car payment.


#9

So I ask as a board of “car people”,what should we do and what advice should we give when the public posts that they used to get better than EPA projected mileage but now only meet projections? I don’t really want to tell the OP to spend any money looking for the cause of this reduction, but should I?


#10

“It crumbled the valance, and punctured the radiator and the oil pan cooler. It was hemorrhaging coolant and transmission fluid. They originally just replaced the oil pan cooler and things related to that, but it seems that in moving it off the road, damage was done to the transmission itself…” When did it start hemorrhaging transmission fluid? From the impact or from the move? Nevermind.

What’s behind the transmission? The fuel tank.

Let’s assume a 20 gal fuel tank, which you used to burn through in 4.5 days (at 25 mpg) and now burn through in 3.65 days (at 20 mpg). Is it possible that you have acquired a small leak in your fuel tank?


#11

I think that you need to wait until the summer blends of gasoline are back and wait for summer temperatures as well. You will get lower mileage through the winter.

I think you should also make sure to calculate your gas mileage using actual miles driven/actual fuel used rather than going by “miles per tank.” And even if you are doing some actual math doing it on a tank by tank basis is not very precise because you have to depend on the gas pumps auto-shut off mechanism. One time you get an extra .5 gal, the next time .5 gal less, etc. The next time you fill up, set your trip odometer and keep your gas receipts. Calculate the mileage over about 1-2,000 miles.


#12

I would suspect wheel alignment, dragging brakes, change thermostat if over 5 years old.
Is the replacement transmission properly going into overdrive and torque converter lockup?
Engine RPM the same as before when cruising at highway speed?


#13

Well, I spoke of miles per tank because I was thinking more of the way it all adds up. But I’ve been tracking the mpg off the car’s trip computer, which will tell me, and off the old ‘fill up the tank, see how many gallons I’ve used, and divide the number of miles on the trip odometer’ (to make sure the computer has been accurate).

The car has two trip odometers, which is handy, because I always leave one unreset (prior to my car trouble, trip A had 10,000 miles and an average of 24.5mpg) And over this last fill-up, I managed to get the mileage up to 22 mpg, and over the last 1000 miles, it’s been 21.


#14

Immediately. My dad hit the rock, got out of the car, saw the fluids, presumably swore a great deal, and then realized that leaving the car (and the rock) on the wrong side of a blind turn was only going to end in tears :wink:

Would the mechanics have noticed a fuel leak? They did have my car in the shop from mid-november until just a week or two ago.


#15

Technically speaking, I was only actually getting slightly better than the EPA mileage on average, and I attributed to the fact that I was basically never did anything but rural highway driving…in Nevada. Even in my old explorer, I got decent gas mileage going in a pretty straight line at 55mph for a few hours).

But in any case, I’m not looking to spend money. It’s just that after having such major work done on my car, there’s a narrow window for me to identify problems related to all the work they did and get them fixed. (For example! one of the mechanic’s assistants left a very important bolt untightened, and as a result, I had to get the car towed 120 miles. And that was just two days ago.)


#16

EPA changed the way it calculated mpg ratings around 2006. For example my 2000 Blazer 4wd was rated at 16/20, now EPA rates it at 18/20. EPA has mpg ratings at this link.

http://www.fueleconomy.gov/feg/findacar.htm

Ed B.


#17

Thank you! That’s a very interesting site.


#18

May I offer a correction? They had your car in the parking lot from mid-november until just a week or two ago. It’s not necessarily the bottom of the tank that’s leaking, so no, the mechanics wouldn’t necessarily notice it.

So it was hemorrhaging transmission fluid, implying damage, then more damage was done in the course of moving the car? Doesn’t sound impossible, just making sure I understand the narrative.


#19

Honestly, I can think of three things:

First one is that they put in a transmission that has different gearing than your original one had. That would directly affect the fuel mileage. The only way for you to tell if this is the case is if you remember what the rpms used to be in top gear at a specific vehicle speed. Most people don’t have a clue about how their car runs, so I’m not really expecting you to know the answer to this.

The other thing is sloppy work that either left something disconnected, or damaged (think wiring to the transmission), or the transmission itself is under or over filled.

Finally, the very last thing is that the transmission is really tight from its rebuild, and needs time to loosen up before the gas mileage gets back to what you are used to.

BC.