Shell Gas - Worst MPG in over a year...

A lot more data needs to be presented before the root cause can be nailed down.

Is the 40 mpg from the displayed value or your hand calculated value?

Has there been any changes in the weather? More winds? Cooler temperatures?

Has your commute changed? More short trips?

 

Thanks for the quick response. Since it is the displayed value, it removes over/under fills of the tank as a culprit. If your commute has not changed and you haven't been experiencing windier weather, it could be one of three (or partials of all 3) things. I'm assuming you know these, but I'll list them, just to be sure.

1) Cooler temperatures will reduce your MPGs. Are the numbers you are seeing comparable to what you were seeing last year at this time or in the winter?

2) Winter blend gas may have been introduced. It won't account for this massive drop but it will contribute. Do you have the option of 100% gasoline, or do your stations serve up only 10% ethanol blend?

3) Tire pressures - If you haven't already, do check your tire pressures to ensure you don't have a tire that is low (slow leak) that would have coincided with your most recent fill up.

Does anyone else drive your car? Have you or another drive inadvertenly hit a curb or otherwise knocked the wheels/tires out of alignment? With such a sudden drop, I'd think it was either weather or wheel/tire related. But the proof will be when you fill up at your local gas station (the "cheap" one and see if your trip MPG's bump back up again).

I'd say before you do that, to reset one of your trip monitors (Trip B for example) and see if you are still seeing the low 40 mpg still, or if there was an event that caused an inital low value and you are slowly recovering from it. The true test will be with filling up at your typical gas station though.

 

When 'cleaner gas' removes all those deposits, where do you guess they go? The only way out of your engine is through the combustion chambers and out the exhaust. It would be good in the long run, but I am betting short term, it reduces efficiency to have inert matter passing through.

 

I wonder if the extra detergents in a tier 1 gas would have a temporary effect of reducing mpg when put into a vehicle that hasn't been running tier 1 gasoline.

 

You seem to have a handle on the car and your situation. I will be curious to see updates on this thread after your next few fillups. My only recommendation is to run this tank a bit longer, thus if there is anything "unusual" in your current tank, its contamination into your next fill up is lessened. (For example If Brand A = 50 mpg and Brand B = 40 mpg, if you filled up with Brand A after using half a tank of Brand B, I'd expect around 45 mpg. If you filled up with brand A after using 90% of brand B, I'd expect values closer to 48 mpg)

 

When do you expect to fill up next?

 

I will not pay a 20c/gallon premium for anyone's gas. I was running with Citgo because they were cheaper until they went to 2 tier pricing. The 2 remaining Shell stations dropped their prices so I've been running Shell since. Citgo has since dropped the tiered pricing and their price so I'm considering returning.

Not knowing what you pay for gas I used a rough local estimate of $3.40 & $3.60/gallon. To break even on the cost you will need to raise your minimum 44 to 46.6 and your max 47 to 49.8. I don't believe the gas makes that much of a difference.

I received a Wawa gift card so bought gas there just to use it up. Never again. The car felt like it didn't have enough power to get out of its own way. So, although I'd say give the Shell gas 2 or 3 tanks to see if you do get those miles, I also say do what works for you.

Xur, I'd like to see the experiment continue because I'm interested in the outcome but I don't blame you if you cut your losses at 1 tank. There are just too many other variables affecting fuel economy that pinning down a cause is impossible.

For example, I know this tank is going to be poor because it's been cold & rainy (at best) on its first 2 days & I don't expect tomorrow to be much better.

 

I don't use anything buy Shell and have never had an issue.

 

I think you've hit winter gas. It can drop my MPG at least 10%.

Try another gas station, you may find the problem persists regardless of brand.

 

For an extra 10 cents a gallon here in town, I've been contemplating the benefits of the cleaning agent Techron in Chevron gas. Does anyone have any experiance with using Chevron gas. Is the extra price of the fuel worth its added cost? I understand that all the different octane levels of the fuel have the Techron available.

 

I highly doubt it. Seems like marketing mumbo jumbo to me. But then again, I'm not an expert.

 

I would assume the difference between detergents to be fairly negligible. I would assume the long term difference between detergenated vs non detergenated gas to be much more substantial.

 

Here in the Seattle area, my records show a distinct mileage drop whenever I use Chevron. Chevron gas used to be the most expensive brand, but its price is the same or lower than other brands now. I suspect they've started blending in alcohol like Arco does.