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Posted by: DaveSause May 31 2012, 11:31 AM

Nice writeup ... but what you don't say is that you actually took the trip mileage and divided by the gallons to determine an accurate MPG. You CANNOT trust the MPG guage. Try this, after you have reached cruising speed on a highway on a level surface, with cruise and ECO on - hit the reset on MPG. You may find that when the guage registers it will say something crazy like 99.9 MPG and it will begin to go down. At other times it will hold 50+MPG for quite a while and only gradually will settle to something realistic. Typically my gauge without messing with it reads about 4-5 MPG higher than the actual I calculate using gallons and miles.

Now here are some other interesting facts. When you first fill up, what does the gauge say for range to empty? In my case it always said 322 and I must also say that I was using 87 octance with the standard "up to 10% ethanol". (2012 Elantra limited, tech package, automatic). I also have a 2011 Kia Optima EX which is the 2.4L GDI engine, fully loaded and it normally says 352. I have found in the Kia if I fill up with 87 no ethanol, 89 no ethanol or 91 no ethanol the guage immediately reads higher, like up to 450 miles. It's amazing to me that it analyzes the octane mix and makes a different calculation. On the Elantra I see smaller changes - it might say 340-360. I'm still experimenting, and trying to see if the increase is real and financially justified.

One other issue has an impact. The owner's manual says that either 10W30 or 5W20 oils are OK, but my dealer said there was a service bulletin indicating that 10W30 could cause engine noise and they were reluctant to put in the Castrol GTX 10W30 I provided (and which I've used for 20+ years in all of our cars). I did some reasearch and found that synthetic oils have better high temperature protection even in lighter weights. I also found that Castrol gives 150,000 or 250,000 or 300,000 mile engine warranties by registering on line and saving receipts showing that you used the indicated oil. So now instead of $6 per quart GTX 10W30, I use $10 per quart Edge Titanium 5W20 to get the maximum warranty. Again, the impact was more noticeable in the bigger engine - it seemed to run quieter and had more pep. On the Elantra, it's more subtle. It used to be that lifting off the accelerator immediately produced a drop in speed, now it seems to coast and lose speed more slowly. I believe I am getting better mileage, but I am not sure yet. Oddly the Kia gets within a mile or two per gallon that the Elantra does. Best mileage so far on Elantra, 35.59 MPG all highway, 10W30 oil, 87 no ethanol. Best on the Kia, 32.68,
all highway, 90% highway, 10W30 oil, 87 no ethanol. I conclude that the larger engine doesn't strain, even with the bigger car.

Dave