“55mph on the interstate for 300 miles and I guarantee you will see over 30mpg in the vibe.”
He’d better stay in the far right lane, in that case
And he’d better not mind that everybody passing him is throwing eye daggers his way
At $3.70 a gal:
- 23 MPG costs 16c/mile.
- 29 MPG costs 12.7 c/mile.
Thus, you would save 3.3 c/mile IF all the work you’ve done had the desired effect…which it hasn’t.
Have you looked at payback on this? It sounds like you’ve spent a lot of $$ tilting at this particular windmill. I think there’s a good chance you’d never get paid back–meaning this isn’t a cost-effective endeavor.
Just accept the car for what it is, and work on adjusting driving behavoirs in search of money savings–there’s usually no cost for “nut behind the wheel” adjustments. And get the K+N off of there–it’s marginally useful for the “go-fast” crowd, assuming they don’t mind additional dirt injestion. For everyone else, it’s not worth it.
It would be an interesting experiment if the OP would do as mentioned above – first fill the tank, then drive the Vibe at 55 mph on the freeway for 100 miles non-stop, then refill the tank and note how much gas it took – and therefore make an accurate measure of the mpg. The reason that 55 mph is important is b/c at freeway speed the biggest force loading on the engine isn’t the tires or the engine bearings, it is the wind resistance. And wind resistance is strongly a function of speed. It is proportionately much less at 55 mph than 65 mph.
So next time the OP has a long freeway trip planned on a flat road in calm weather and there’s a little extra travel time allowed so you can drive at a constant 55 mph, try doing the experiment. It’d be best if the trip was an out and back, 50 miles one way, then 50 miles back on the same route, to reduce wind speed effects. It seems like if did that and you don’t get at least 29 mpg, you’d have a right to complain to the folks who sold you the car and/or the manufacturer.
Given everything that’s been done, the only other thing that I can think of is that the thermostat is opening too soon, or stuck open. A long shot, but not too expensive to change out.
But my bet is on ‘it’s normal’.
I would get the ECM reprogrammed, or reinstall the original. Otherwise you won’t know when there’s a real problem kicking on the check engine light.
For one thing at 100K you need new plugs and possibly wires. It may be running a little rich due to a sensor problem but you’d need to have a diagnostic computer put on it to see what the fuel trim is to see if that’s a problem. Personally I’d take that K&N out and put the stock back in. Driving styles can have much to do with mileage. Jerky starts and stops, too much up and down on the accelerator, etc. But bottom line, unless you’ve got a lot of extra weight in the car, you’ve got a little engine working hard to propel the car. Engines working hard take more fuel.
Be sure you are checking the gasoline mileage the old fashioned way by filling the tank and noting the odometer reading, driving until you need to fill up again, record the gallons used, and repeat this process several times. Finally, at the last fill-up, note the gallons put in the tank, subtract the original odometer reading from the present odometer reading, divide the gallons used into the distance traveled and then you will have a pretty good mpg average.
You may want to be sure the odometer is accurate. The car may be travelling more miles than is recorded on the odometer. I see you have 17" wheels–is the tire size what is specified for the car? If the tires are oversize, this will change the odometer reading by making it read low.
Finally, the car may be in perfect tune, the gas mileage measured accurately and the car still may not do as well as expected when compared with larger cars. I had a 1971 Ford Maverick with a 250 cubic inch 6 cylinder engine. The best mileage I could record was 21 mpg. I traded for a 1978 Oldsmobile Cutlass Salon with a 260 V-8 engine. The Oldsmobile was a heavier car with a larger engine, yet I could record 24 mpg on the highway. I also got better mileage around town with the Oldsmobile. I kept the Maverick in perfect tune. The mileage on the Maverick wasn’t what I expected, but that was not the reason I traded the car. I got rid of the Maverick because it rode like a wheelbarrow and I was traveling quite a bit at the time, and not because of the mileage. It was doing the best it could do. When I found I was spending more on Preparation H than upkeep on the Maverick, it was time for another car.
My dad and my brother both had 1963 Buick LeSabres. My Dad’s LeSabre had a 401 cubic inch V-8 engine, power steering, power brakes, air conditioning and automatic transmission. My brother’s LeSabre had a 364 cubic inch engine, no power steering, brakes, or air conditioning. It was a 3 speed manual transmission. On a 350 mile trip where they drove in tandem with my brother and his wife in one car and my Dad and Mother in the other car, my brother’s mpg was 19.1. My Dad’s mileage was 19.7 and he ran the air conditioning.
If everything in a car is up to factory specifications, then the engine gets the mpg it was designed to get.
One last thought on gas mileage. I had a 1990 Ford Aerostar when my son was a new driver. The Aerostar was the Eddie Bauer model and had an mpg readout. My son consistently got the best mileage of anyone else that drove the vehicle. I was so jealous that I wanted to ban him from driving the Aerostar. My son has always been a calm, easy-going person and it is reflected in his driving. Driving styles do make a difference.