Poor mileage on a Cadillac SRX

I bought a Cadillac SRX last March, 6 cyl. When I first got it and I fill up with gas I was able to pump a little more than 18 gallons and the mileage range would always be 410 miles according to the computer. I notice over the summer that the miles range was dropping down to 380-390. I called the dealer and they told me that was normal because of my driving habits. In the fall I noticed that the mileage range dropped down to 350-370 whenever I will fill up and I was no longer able to put in more than 17 gals. I called the dealer again and they said the same thing. In the winter the mileage ranged dropped even more to 320-330 when I would fill up again no more than 17 gals. I called the dealer again and they agreed to look at the car. They told me that they updated the computer with the new gas formulas. I was told to drive the car for 250 miles and it should correct itself. I did that but it did not get corrected. I called the dealer again and they took the car in and took apart the exhaust system tested it and found that some sensors were not working properly and replaced them. This time they told me to drive the car 500 miles and that it should correct itself. I drove 1000 miles and still had the same problem. I took a trip to NY and had to fill up on the way back after 290 miles. So the mileage range has now dropped to under 300 miles on a full tank. Once again took it back to the dealer, they kept it a week, made some other updates to the computer and told me it was fixed. They said their mechanic drove it 40 miles and got 20 miles to the gallon. When I asked if he actually filled the tank up and drove it 40 miles and filled it up again. They said no. What they did was drive 40 miles and the computer told them that the average miles per gal. was 20. So I called the salesman that sold me the car expressed my concerns that the computer is not accurate. It will state one thing but when you drive it and manually calculate the mileage it doesn’t add up to the same thing. In fact the owner of the dealership had done just that and got 12.5 miles to the gal. by filling up, driving 25 miles, then filling up again. He could only put in 2 gals. of gas. When I picked up the car this week I got in after being told that the sales person drove 120 miles and filled it up with 7.5 gals of gas and got 17.5 miles (city). I looked that the mileage range whne I got in the car and it said the mileage range was 330 miles on a full tank. When I drove off I noticed the same thing happening. The mileage range was all over the place dropping anywhere between 20-30 miles after only driving less then a mile. Obviously my car has not been fixed and I am getting extremely frustrated. I am filling up twice a week (3.45 per gal) and the dealer is insisting that the car is fixed. What can I do? Can you help me determine what is wrong with the car? I have called several Cadillac dealers and none of them have had issues like this with the SRX. If this keeps up I am going to have to trade the car in for something else because my luxury car is a PIG?

Here are some variables:

  1. Gas pump shutoff sensor sensitivity.
  2. Gas pump shutoff sensor vs speed of fill.
  3. Levelness of gas station pavement.
  4. Driving habits.
  5. This is rare but possible: Gas pump calibration accuracy.
  6. Engine oil viscosity.
  7. Tire inflation pressure.
  8. Summer fuel has more energy content than winter fuel.
  9. Straight gasoline has more energy content than gasahol.
  10. Traffic conditions.
  11. Wind direction.
  12. Air conditioner on or off. (Off will allow better fuel mileage)
  13. Windows open or shut. (Closed will allow better fuel mielage)
  14. Number of passengers and weight of luggage.

To accurately measure your gas mileage, you must refill at the same gas station at the same pump to the same fill level at the same pumping speed for at least two fills.

At 3.45 gallons per fill, twice per week, you are not a heavy user so it is not worth the depreciation to buy another car but you knew that, didn’t you?

It may not seem like much money to you but $120 per week is alot of money to me. We did the filling up at the same gas station thing.
*I live in the state of connecticut not much traffic here. Pretty much just straight driving all the time some highway mostly city miles.
*Tire pressure is fine (34 on all four tires).
*The only thing on in the winter is the heat but in the summer AC was on and I still got better mileage.
*I understand the summer fuel is more energy content then winter but is a 100+ mile drop normal for winter months?
*I usually fill until the clicks are more frequent at the pump. I use the same gas station and the same pump every time.
*I just got an oil change about 2 weeks ago, synthetic Mobil One.
*My driving habits: I am not a led foot. My city miles are under 45 and high miles 70.
*Windows are always closed.
*During the day where most of my driving takes place I am the only one in the car. Weekends and twice a week my 2 children ride in the car
with me and there is no luggage weight.

I can’t afford to keep this car with my car payments + $480 gas expenses a month. My question was has anyone ever came to you with this problem and how was it resolved?

Your problem, from my perspective, is you are expecting too much… gas consumption is an inexact science and varies considerably fill up to fill up. You are going to get extremely frustrated and hate to drive your SRX so why don’t you just forget about calculating every drop of gas you purchase.

Ask someone, whom you don’t intimidate, to ride along with you to observe your driving techniques, on short trips and long. After the observation period, let an impartial person evaluate the report on “this driver”.
On this Web site, go to Actual Car Info, scroll down to Owning?, go to the “improve your gas mileage section”.

the salesman that sold me the car expressed my concerns that the computer is not accurate. It will state one thing but when you drive it and manually calculate the mileage it doesn’t add up to the same thing. In fact the owner of the dealership had done just that and got 12.5 miles to the gal. by filling up, driving 25 miles, then filling up again.

The readouts of those on-board computers of the MPG are well known to be very inaccurate.  They don't do to bad in measuring differences, such as driving 50 mph vs 75 mph.  They will tell you you are using more gas at 75 mph.  They will be inaccurate about the actual mph.  

You will not get anything close to an accurate number by filling up the tank and driving 25 miles and re-filling it.  That is also inaccurate.  

Fill your tank and not the miles on the odometer.  Drive normally until it is almost empty, then re-fill.  Again note the miles on the odometer and subtract to find the difference and divide by the number of gallon just put in.  Repeat three times in a row.  The average of those three should be close and the variation will give you a good idea of how close.  

Give us those numbers along with the EPA estimate for your car and describe your typical driving cycle (how many miles and what kind of conditions (weather stop and go traffic mountains etc.

I’m sorry I thought this forum was for people to talk about the problems they have with their vehicles not “their problems”. I am not expecting too much from my car. I just want to know what is going on it with it and why there is such a difference in mileage driving over the last 6 months. In my opinion, 100 mile difference is a lot to just ignore. It was a simple questions but if you don’t know the answer why don’t you just let someone who does answer instead of trying to belittle my questions.

Thank you for your response. I really appreciate it.

The EPA shows 13-15 city and 20-21 on the highway depending on the model. Driving habits can easily knock 3 or 4 MPG off of those figures even.
The door glass paperwork that is required to be in place should state the EPA mileage figures. Did you not see this when you bought the vehicle, assuming this was a new vehicle purchase?

Also agreed that you should never figure mileage based on a gauge reading or dashboard readout.

I apologize; misread your post to mean that you bought 3.45 gallons twice per week. Yes, the mileage calculators built into some new cars are a little inaccurate. Our last one read about 1 mpg high. Our present car reads about 1.5 mpg high.

All of the car makers send out technical service bulletins to advise car owners to use the octane gasoline shown in the owners manual. They state that the use of lower octane gasoline leads to lower fuel mileage, and degraded vehicle performance.

My question to the OP still stands.
If you bought the car new then what did the Federally required window stickers show as fuel mileage figures?
Here’s what the Feds show.


12.5, 17.5, 20, etc sounds all normal to me and what’s amazing is that apparently not one of these people involved in checking this car has the guts to say “It’s getting just what it’s supposed to get”.

"I usually fill until the clicks are more frequent at the pump. I use the same gas station and the same pump every time.

While I don’t have anything to add regarding the gas mileage issue, I feel that I do have to comment on the point that you made, above. If you want to prevent an expensive problem that will not be covered by warranty, I strongly suggest that you stop filling your gas tank the first time that the pump clicks off.

By continuing to force gas into the tank, you are creating a situation where excess gas will overflow into the carbon canister that is the heart of the car’s evaporative emissions system. Once that carbon canister is sufficiently contaminated with gas (note: it might already be at that point), you will be unable to pass an emissions test and the only “cure” at that point is to replace that carbon canister. My best guess is that you will be looking at a bill for something over $300. at that point, so I hope that you will heed this advice.

As a side note, I have always wondered about what compels people to use this approach to filling a gas tank. If I was about to cross the Gobi Desert, I would definitely be concerned about getting that extra 1/4 gallon into the tank. However, in the type of driving that people normally do, with gas stations everywhere, I cannot imagine why it would be necessary to force this extra bit of gas into the tank. And, to potentially wind up with a very expensive repair bill as a result, makes me really wonder why people do this.

I have a friend who explained to me why he does it. He said that over the course of the year he will have to stop fewer times to get gas, thus saving time. My guess is that, at best, he will save 1 fill-up a year. Hardly worth the risk of contaminating the canister.

Another reason is to round off the figure to the nearest dollar (or, pound) after the pump automatically clicks off the first time. Why? It’s easier to remember a round number when making the entry into, or balancing, the check book.
One has prepaid X dollars (pounds) and want to “hit” that figure to avoid going back inside, and waiting in line for ones change.
Of course, these reasons aren’t worth it when one balances those “benefits” against the cost of repairs to the Evaporative Control System (especially, the charcoal canister).

Whatever happened to paying with a credit card?

I get a few hundred $$ back each year in rebates on the credit card that I use for gas and groceries. It takes less time to pay that way, I get money back, and I don’t have to worry about an “odd number” on the pump. Plus, with the price of gas being what it is, I don’t have to carry a huge amount of cash in order to pay for that gas.