Besides the originator of this topic there are at least a couple others that are going to try it over the next 6 tank, 3 midgrade & 3 regular. At the end of this I am sure we can give you some hard data on that but right now it is going to take a while to burn through those tanks of gas. I am tracking how much gas it takes and what the price is for regular & midgrade at the times of my fillups so I can easily make the comparison. Personally I don't expect a big difference, but that is why I am willing to try it and see.

 

It will interesting to see what those results are. My guess, and it's only a guess, is that any improvement in MPG is probably going to be offset by the price increase, such that the MP$ will be close to flat. It will be interesting to see if the results show differently.

 

I'd bet the mid does no better. In fact, worse. The ECM is programmed to run 87. The lower the octane, the higher the energy. That's why diesel is more efficient. It is somewhere in the 40's. Higher octane means more volatile, more explosive. Gotta burn quicker. And possibly do some damage to the spark plugs. I have noticed when buying gas that if the fuel is ethanol enriched, fuel mileage suffers also. I'd personally stick with the big bucks Honda engineering has in this thing. I wouldn't mess with the tire pressure either. It is summer, and it isn't hard to have a tire pop when running more than reccomended pressure. Fifty cents or life. I'd choose life.

 

I had an old 85 volvo stationwagon and I did the same thing with calculating mileage. I only ever tested it with highway driving because I would drive back and forth between my home in PA and Ohio, and I would test it as I drove the PA and OH turnpikes, which took a little over a whole tank of gas for me. I got 22mpg with regular, 29mpg with premium, and in between for mid-grade. Needless to say, I bought premium from then on.

I have been filling my 2003 HCH with regular and getting 42-47mpg in a mix of city and highway driving (it does better on the highway). I hadn't thought of testing it because the manual said it is fine to use regular grade, but the manual doesn't seem to have any useful info...so...I think I'm going to try mid-grade and see what happens.

Is it worth trying premium too? I read that the old Volvos like mine were actually made to burn high octane fuel. I even noticed a difference between 92 and 93, although I actually got worse mileage when I tried 94 the one time.

I dunno? Thoughts? I'll get back to you too when I try this out.

 

Cazort with the HCH if there is going to be any difference for the positive it would be with the mid grade since it is setup to burn regular. Premium has far too many additives, anti-knock, detergent, and who knows what else to really bother with trying at this time. Lots of older vehicles did need higher octane, but that was before computers controlled the process and lots of high performance engines still need it, but I would hardly call the HCH's engine high performance. Before you try it you might want to find a plateau for you mpg with regular. If you are bouncing between 42-47 you really haven't gotten to a steady average yet. I average around 55 mpg pretty steady and that is all back country highway driving at around 45-55 miles per hour. It is creeping up right now but that is because the average temp is climbing. I just filled up with my first tank of mid grade. One of the reasons we proposed trying this little experiment now is because by the time we switch back to regular summer will be at its warmest and regular will have a slight advantage temperature wise. Didn't want it to be the other way around and skew the results in favor of the mid grade.

I gather you just purchased your HCH and it is still teaching you some things about how to drive it and yes most that love their HCH know that it can teach you how to save gas if you let it. Let the 2 or 3 of us spend the extra money to test this theory and you can find your average mpg in the meantime. Then wait and see if you agree or disagree with what we find out over the next 3 months, and you can adjust your fuel purchases accordingly.

I log my mileage here and at cleanmpg, if you click on the part of my signature that has MPGus on it, you will see my mileage along with other notes concerning temps, tire pressures, and whatever maintenance I have done recently. I have expressed this opinion before but I will say it again, I really don't think the increase in mpg, if there is one, will be significant enough to warrant buying mid grade all the time.

 

Cazort,
I have tested regular, mid grade, and premium ( 2 tanks of each after 5000 miles break-in) on all my cars since about 1980 and only found premium to be the best bargain on a 1989 Honda Accord. It was a marginal difference above mid grade, but still cost effective.

BTW: The 2008 HCH manual recomends 87 octane or higher.

 

That's the problem I have with experiments like this, and ESPECIALLY with this one since it requires a whole tank to test. My mileage is all over the place on a day to day basis, even though I drive the same route at the same time at the same slow speeds. I got a 56mpg yesterday morning and a 63mpg today--probably due to temperature swings. Coming home is even more of a swing because I might be in the mid 70s on a really hot day and mid 50s if it's cold. Throw a week of cold weather into one of the tanks and that could have a significant impact.

Now throw in a couple extra super short trips to the grocery store with one tanks, or a trip on the highway and that tank is either going to have a lower score or higher score because of difference. When a tank gets you between 6 and 7 hundred miles, there can be a lot of variablity in how those miles were driven--even if 75% of the mileage was standard day to day commuting.

I'm not posting this because I'm skeptical about this experiment--I love the fact that people are always out there trying to find the best ways to get high fuel economy! However, I do think it is extremely difficult to get an apples to apples test that would have conclusive results one way or the other...

 

The HCH has a 10.8 to 1 compression ratio. Normally, this kind of compression would call for higher octane fuel to prevent knock. The motor has a knock detector that retards timing when knock is detected. So life is good. But what happens when timing is retarded to prevent knock - say in the hot summertime? You lose a bit of power. So now there is a choice of pushing a bit harder on the throttle, or not. If you don't push a little harder, it takes longer to get to your cruising speed and perhaps digging into your battery -and that takes gas to recharge. You do push a little harder on the throttle, and that takes a bit more gas to get to cruising speed. I don't have enough miles on my HCH to draw any conclusions, BUT -

My test car for this was a 2003 Honda Accord with 4 cylinder and many long trips. Mid-grade, (conclusively for me), did two things in warm/hot weather. It stopped my timing from retarding between 2000 and 3000 rpm (that doggy feeling went away!!! happy dance!), and I gained on average 2 mpg. Sometimes 3.
Sitting down with a calculator after a few trips, I determined it was a wash. Higher fuel costs killed savings from better gas mileage.

This Accord is my wife's car now, and when the temps go above 80 degrees, we fill 'er up with premium. My wife hates that doggy car feeling... and I'm smiling cause its not wasted money cause of the slightly better FE.

I suppose I'm saying that it is probably true for some drivers that when temps go up, the HCH is going to benefit from mid-grade. With the usual caveats that YMMV!

 

And I agree with you 100%. But for me I would prefer a real life test instead of just sticking the car on a dynamometer and letting it run for a tank of gas. With three tanks of gas of each I should be able to see if it is making enough of a difference for me to consider continuing buying mid grade fuel. As I have said before I am even giving regular the benefit by being the weather being warmer then and even having more experience with the car. There is nothing scientific about it and I certainly am not trying to claim that. It's only costing me an extra 1.30 a tank so it is not going to break me. It's just something to try. We shall see what we shall see and as always YMMV.

 

Finished partial 3rd tank.

Driving was not consistent with my regular trips. I carpooled for 3 round trips to work (275 mi.) with 2 of my lead footed co-workers and about an extra 100lbs. of equipment and tools in the trunk. I even let them drive to work to get the feel of Hybrid driving techniques. I guess they didn't do too bad because my mpg ended up to be around 59mpg.

I am surprised how good the mpg is! Maybe it's the outside temp. I used air conditioning (set to 72 degrees) for half of the miles. I keep my tire pressure at 44psi.

We live on flat land around here. The only bumps in the road are bridges and inclines for rain drainage. But, anyway, I ran this tank short to get back on track with testing.