Getting worst mpg when your oil is full?

[schumionbike]

Lately, I have been making sure that my oil is at the full mark. Before, I usually leave it at between the L and F mark. For some reason, I noticed a slight decrease in my mpg. I use to get 29-30 consistently. Now I have change my plugs, wires, tires, transmission fluid, differential, new aligment and the last few tanks I have been between 27-28. What's is up with that? Maybe it's just that my route are a little different since my parents has been in town and I'm showing them around might have cost some mpg. I don't think I overfill my oil, it's at the full mark when the engine is cold. Anyone want to explain this? As I have no idea. Maybe the car is just getting older.

[uibalnme]

1) The added weight of 2 passengers(or any added weight really) will decrease MPGs.

2) you should check fluid levels when the engine is at operating temperature, not cold.

Drive a couple of miles, then park the car. With the engine still running, check the trans fluid level. That's the only fluid you have to check with the engine running. After that, shut off the engine, and check the oil level, and add if needed. I'm pretty sure you'll have to add some oil. It should be slightly above the full mark when cold.

[JohnGD]

From your list of variables, I'd say tires and alignment are probably the most significant suspects besides the temporary driving style change.

What tires were you using before/now? How were the alignment numbers? What plugs and wires are you using?

Originally Posted by schumionbike

Lately, I have been making sure that my oil is at the full mark. Before, I usually leave it at between the L and F mark. For some reason, I noticed a slight decrease in my mpg. I use to get 29-30 consistently. Now I have change my plugs, wires, tires, transmission fluid, differential, new aligment and the last few tanks I have been between 27-28. What's is up with that? Maybe it's just that my route are a little different since my parents has been in town and I'm showing them around might have cost some mpg. I don't think I overfill my oil, it's at the full mark when the engine is cold. Anyone want to explain this? As I have no idea. Maybe the car is just getting older.

[schumionbike]

I had an old set of Bf Goodrich tires on there before, it had about 42 K miles on it when I replace it with a set of Goodyear Viva 2 tires from Walmart. The Bf Goodrich had very good mileage on it until recently. Both of the tires are standard 195/70R14. They didn't have to adjust much when I had my alignment done as the car was within specs anyway for the most part, I do feel that the steering is more neutral though.

I'm using Bosch Platinum 2 (think that's the name) plugs and NGK wires. The old plugs were NGK. Not sure how many miles were on those when I replaced it. They look to be in okay conditions. I had like 3 K on the new plugs. Oh, I didn't hear that Bosch are not well suited for our car until after I put it in. The guy at Advance Auto say that was OEM...I should have done a bit more research. Hopefully these plugs will be okay for a while. The car have 183K miles btw.

[skewe]

Driving style
Route
Additional ppl in the car

[chronoti]

heavier tires will kill millage the tires that "improve millage" are just light weight

[73sport]

I think you all nailed it ^^ John esp with tires and tire pressure.

Heck, if someone had the old tires at 40PSI and then the new tires were set correctly in the low 30's, that could get the numbers you speak of MPG wise coupled with a different tire design. . . .

Not likely oil fill related. Well . . . When out of oil it won't travel far so mpg should be less of an issue!

[Mike Gerber]

One more thing to consider. As the temperature has warmed up a bit are you now using the A/C, where you might now have used it before, or might have used it a bit less? Running the A/C, especially in city traffic will greatly effect fuel mileage.

Mike