Sudden mileage drop

[Jake's daddy]

OK, Gearheads. I need some help figuring out what's going on with my '05 CC. For over four years now, I've been averaging 16-17 MPG, daily driving. In the last few weeks, it dropped to barely 14 MPG. Driving conditions and habits haven't changed. If anything, I'm using less right foot than before to see if that will bring the MPGs back up. Cleaned the air filter. Checked the pressure in the tires. Recent services included rear differential and an oil change. I switched to Pennzoil's High Mileage stuff. Could that be it? I'd appreciate your feedback. Thanks.

[TwoBills]

That high mileage oil is 10/40 isn't it? That could be it. I'd also check for codes. Maybe a sleepy O2 sensor.

[devious1]

It could very well be the oil if that is the only thing you have changed besides the filter.

[Jake's daddy]

Thanks for the feedback. I checked my service order; they used 10W30. Is the O2 sensor something fairly easy/inexpensive to replace? Any other suggestions?

[RedAlert]

Try using the 5w30 that the manual calls for. I would imagine the 10w oil could drop you that 1-1.5 mpgs. For 15 bucks of oil, it would be an easy enough thing to help narrow it down. You dont even have to change the filter

[Fear Night]

I'd guess something is different with the gas you are getting. They may have some water leakage in the holding tanks or have added more ethanol than you were getting before. There is one local gas station that I cannot fill up my motorcycle at. I fill it up with 93 but it pings like crazy and can hardly idle. Never had a problem with any other station.

5w to 10w shouldn't cause a 3mpg drop alone, that's pretty significant.

[Jordo]

Originally Posted by Fear Night

I'd guess something is different with the gas you are getting. They may have some water leakage in the holding tanks or have added more ethanol than you were getting before. There is one local gas station that I cannot fill up my motorcycle at. I fill it up with 93 but it pings like crazy and can hardly idle. Never had a problem with any other station.

5w to 10w shouldn't cause a 3mpg drop alone, that's pretty significant.

Its the phucking ETHANOL!!! I'm about to do a thread on this! There is a Getty gas staion by my house that is selling gas with no ETHANOL!!! My MPG went up about what yours droped.

I have to finish this tank of gas, which should be by the weekend, and I'll do a little write up.

[Fear Night]

Originally Posted by Jordo

Its the phucking ETHANOL!!! I'm about to do a thread on this! There is a Getty gas staion by my house that is selling gas with no ETHANOL!!! My MPG went up about what yours droped.

I have to finish this tank of gas, which should be by the weekend, and I'll do a little write up.

Yeah, I hate ethanol. The EPA is pushing to make the maximum ethanol concentration cap 15-20% instead of the 10% cap now. Do they want us all to have sub 10mpg? Idiots. Car companies are pushing back saying the engines can't handle that much and they won't be able to honor warranties.

Price stays the same, but we get worse MPG and end up at the pump more. More profit for the gas companies because they can dilute down their gasoline and sell 10+% more. Then farmers ride the corn wave all the way to the bank. What a brilliant business plan, sounds like a bunch of mutual back scratching to me.

[q-ball]

StarBrite marine products makes stuff called enzyme

Star brite - Catalog - Product Detail

it is suppost to help with all of this ethanol BS!!!!

[Devius1]

Adding to the list..
When was the last time you cleaned the MAF sensor?