Lower gas mileage

[FocusRun]

Hi Guys! It's been a while since I've been here. I hope all is good, especially now with Christmas coming.

I was hoping you guys might help me out. See, Mr. Lemon (Ford Focus) is sorta not running right. His gas mileage is dropping. When I got him 2 years ago, he was running 29/30 mpg. During cold days with properly inflated tires, he would be running at 27/28. But now... He's running 27 at best and and as low as 25 miles per gallon.

These might be the cause, please say which most likely is the one.

Instead of going to the dealer for the 5000 miles oil change, I've been going to Mavis for oil change every 3000. Would that lower my gas mileage if Mavis is using a different oil for Mr Lemon instead of the 5w20 recommended by Ford.

Here's another one. I bought 2 new tires (P195/60-R15 89H). they're SLIGHTLY bigger than the orginal(P195/60-R15 87H) for my front wheels with the intent of buying the same set of tires for all fours. Would slightly different tire size actually lower my gas mileage that much?

Or do I need to complete the set and have an alignment plus balancing?

Thanks Guys!

[BradE]

How many miles on the vehicle?

Bigger tires could cause the MPG drop. Even if they used 5w/30 instead of the 5w/20, I doubt you would see that much of a drop in mileage.

[FocusRun]

it has nearly 45000 on it

The new tires are General Exclaim.. Anyone heard about / uses it?

[BradE]

Check your air filter and other general stuff at that mileage if they have not been replaced yet. Ford's are picky about fuel filters, and if they are not changed it will tank your MPG.

I'm not familar with the engine in the Focus, but I know in the Ford trucks the 100K mile platinum plugs last about 60K before they start going downhill. Your mass air flow sensor could probably use a cleaning too.

Other than general upkeep stuff, your tires might very well be the problem.

[Dr Groove]

Focus run...

I'm thinking it might possibly be the gas that oil the companies are selling us in the winter here in the NE, I'm in NJ. I believe they change over to an "oxygenated" fuel sometime in November.

My experience has been about a 2 mpg drop during the winter months. Sure I know in part that's due to running the car longer in the morning to get it warm, etc. but I think it just might be the "winter gas" your putting in the tank.

[Dave Holmes]

Check your basic maintenance items (fuel filter, spark plugs, PCV valve, etc...). A lot of manufacturers are going to "extended" life platinum plugs, but they may already be wearing out at 45,000 miles. Little things like tire pressure or type of gas can affect your mileage a few points, too. And like Dr Groove said, fuel companies are probably switching over to winter "oxygenated" fuels, which will affect mileage and performance.
The tire sizes you wrote are the same size from my understanding of tire specs. P195 means they are passenger tires, with a 195 mm tread width. 60 is the sidewall aspect ratio (60% of tread width). 15 is rim size. The 87H and 89H are the load rating. It is perfectly fine to go up on that number, but not below what the vehicle manufacturer recommends. It doesn't have any bearing on size, just what it can handle.
I believe tirerack.com has more info on how to read tire sizes/specs on modern tires. Like I said, the above is my understanding of what the numbers mean. Someone correct me if I'm wrong.

Hope this helps.

Dave