I've done plenty of checking on mileage vs. speed in the 27,000 miles I've accrued so far.

When I used to drive 70 mph, I would get about 25 or 26 mpg average for a whole tank. In fact I think I posted this a few months ago, and I believe it was here. If not, might've been at Edmunds - used to go there but don't anymore.

Now that I drive 55 mph, I get about 30 or 31 mpg average for a whole tank. I have ample documentation of that if you'd like, as I've gotten over 500 miles on each of my last 4 tanks and averaged over 30 mpg for each of those tanks as well. I know it makes me a huge geek, but I like to record my 500 mile tanks. Perhaps if each of them continues to be 500+ miles the thrill of this will wear off, but it's pretty cool now anyway.

This is all pre-Mobil 1 5w20 oil, which I went to over the weekend. I'm hoping there will be an additional increase in mpg, but even if there's not I'd be happy with better protection and longer engine life.

As far as optimum efficiency goes, 55 mph is probably not it. It's probably lower than that. One of the car mags I read monthly (Car and Driver, Motor Trend), and I can't remember which one, did a test recently using a Lexus hybrid to determine at what speed the best mileage was returned, and it was much less than 55 mph. I drive 55 mph because it is the speed limit, and also happens to return some pretty good mileage. If I really wanted to be anal, I'd go 50 mph but I do have my limits. :innocent:

Update: Still looking for where I posted my higher-speed mpg but can't find it. My first post here was around the beginning of March, which was also about the time I started driving slower in order to save $, so maybe I didn't post it here. Before then, I would go 65-70 pretty much the whole way and was lucky to get over 26 mpg, avg, for a tank.

This post has been edited by mc229: Apr 17 2006, 05:47 PM

It would be interesting to see what gas are you saving (if at all) with the new syntethic oil ...

Don't worry, I'll keep you posted. It will probably take more than a couple tanks to get an accurate read on it, though, since weather and other factors play a role.

I really didn't get it for mileage's sake, though - wanted to better protect my engine for the long haul, since I put miles on so quickly. I'd like to keep it for 200k-300k miles, which at my current rate would be 3.5-5 years. I know that a lot of that is just getting a good car/luck of the draw kind of stuff, but I want to do my part by always using the best products for upkeep and maintenance, and not just driving the snot out of the car.

Here's to hoping for a long and healthy life of the Sonata!

:beer: