A real puzzle!

So I’ve always wanted to see the Rocky Mountains. I flew to Denver and when I was picking up the rental car I was told I’d need a 6 cylinder to drive in the mountains. One of my options was a 6 cylinder 2010 Forester. Funny, but 6 months ago I just bought a Forester, had done research, and didn’t know there was a 6 cylinder without the funny hole on the hood, but I went along and got the Forester. Then, driving in the mountains the car indicated we were getting 28miles per gallon of gas. I was shocked! I’ve never gotten anywhere near that in my 4 cylinder.

Does anyone have an explanation or information about this?

Those gas monitoring systems telling you your mpg is notoriously INACCURATE. After you filled up how many gallons did it take and how many miles did you drive…do that 3-4 times and take the average…that will be a much more accurate of you TRUE gas mileage.

A V6 can get better mileage than a 4 cylinder, if the 4 cylinder is being overworked.

There is a very simple explanation, namely that there is no 6-cylinder engine available on a Forester!

So, whether the car has the “funny hole on the hood” (known to others as a hood scoop) or not, this vehicle has a an H-4 engine. The Foresters with the “funny hole” have a turbocharged version of the H-4 engine. Even though this is a powerful engine, it is not a 6-cylinder.

The only possibilities that come to mind here are:

The rental agency sold you a “bill of goods” and wound up charging you for a 6-cylinder model while actually supplying you with a 4-cylinder model.

You may have been driving the rental 4-cylinder Forester more cautiously than you normally drive your 4-cylinder Forester, thus yielding better gas mileage.

The 4-cylinder rental Forester may have had overinflated tires and/or the tires on your Forester are underinflated.

You may have been driving an Outback, rather than a Forester.
Some Outbacks have an optional H-6 engine, and as tardis observed, a 6-cylinder engine can get better mileage than a 4-cylinder engine under certain circumstances. The Outback with the H-6 engine is rated at 18 mpg city/25 mpg highway, with some drivers reporting mileage slightly better than that rating. (sorry, tardis, no V-type engines on Subarus!)

You may have been driving a 4-cylinder Outback equipped with the Continuously Variable Transmission. With that combination of equipment, it is rated at 22 mpg city/29 mpg highway, with many owners routinely reporting mileage of 31-32 mpg on the highway.

But, no matter which of the above possibilities may be the case in your situation, the bottom line is that you could not have been driving a vehicle that does not exist, and there is no such animal as a 6-cylinder Forester.

Edited to add:
Did this rental agency by any chance have any 4-door Camaros available?

There are many factors that determine gasoline mileage. The number of cylinders is often not a factor. Back in the early 1950’s, the Cadillacs actually did get good gasoline mileage for the time and the Cadillacs had a V-8 engine. A 1951 Cadillac model 61 would get better mileage than a 1951 Chevrolet equipped with the PowerGlide automatic transmission under most conditions. Why? The Cadillac had a 4 speed automatic transmission while the Chevrolet PowerGlide depended completely on the torque converter and had a lot of slippage. In fact, Chevrolet equipped the engines of the cars equipped with the PowerGlide with hydraulic valve lifters, because the engine had to rev up so much to overcome the slippeage that without the hydraulic lifters, it would have had a lot of valve train noise. The Cadillac engine was newly designed and appeared in 1949. It was quite efficient for the time. It did have a higher compression than the Chevrolet engine and probably required premium fuel while the Chevrolet engine ran on regular.

The Forester you rented was the turbo-charged 4-cylinder model. The hood scoop ( funny hole) feeds air to the intercooler. Never mind. The turbo 4 has power similar to a V6, but doesn’t use as much gas. Unless you floor it all the time. As far as I know there is no 6 cylinder engine available in the Forester.

The rental agent is pretty good at squeezing extra money out of customers. A normal 4-cylinder would have been perfectly adequate for touring the mountains.

I can’t explain why your Forester doesn’t get better mileage. Do you drive in the city all the time. My 4-cylinder Legacy regularly returns 27-28 mpg, and will sometimes do better on the highway.

That mileage is not the average mileage, it is likely the current mileage, which will be low going up hill and high doing down.

There is no reason a four cylinder car can not be driven in the mountains. I have drive three different 4 cylinders in the mountains, including one with only 1,200 cc engine.

McP–Read the original post again!
The OP states that she “didn’t know there was a 6 cylinder without the funny hole on the hood”.
I think she was telling us that the rental car did not have a hood scoop.
No hood scoop on a Forester=no turbocharger.

More and more, I am beginning to think that she may have been driving a new Outback–none of which have a hood scoop on the 2010 or 2011 models, but do have the option of a six cylinder engine.

One way to tell is how the roofline curves down in the back. A Forester has more of a boxed look to it, while the Outback has a slope to the back end. Or it could have been neither of these and could have been a Tribeca

After the fact, I doubt that the OP would recall details like the rear slope of the roof.