Clusterboard Problem: Related to Very Low MPG?

the car is reporting correctly. (despite the fact that it tends to be optimistic) so you are probably getting high thirties mpg.
your problem is the gas tank bladder, which often doesn't allow consistent fill amounts.

you need to start tracking your measurements at the pump, and averaging them out.

another problem will be the $600. rebuilt battery, which likely won't last very long.

 

It's hard to think of just one thing that would give you that bad of fuel economy short of towing a fully loaded tractor-trailer rig behind your Prius.

Not having LRR tires will hurt pretty badly. So will dragging brakes. Hard stopping is a tremendous fuel waster. Hard acceleration is almost as bad. A low 12V battery will also be a power drain since the car is working harder to charge it, but not all that much.

I don't see how a bad CM will affect your efficiency, but I would get it replaced so you know if you should expect flashing red and blue lights in your rear view mirror, if nothing else. Another thing to keep in mind is that I don't think the odometer is working when the CM isn't working. So you're probably going a lot farther on a tank than the odometer says on those occasions when the odo lights up. I could be wrong about this, though.

As @bisco said, a rebuilt battery is one of the surest ways to buy trouble. What you have isn't likely to be hurting you now, but it will do so way sooner than you will like.

 

The clusterboard has know bad solder problems, try toyota for a possible warranty

The traction battery....
If replaced with a new Toyota traction battery 2,500$ (Installed) will give five years of like new mpg’s, as long as the wheel bearings aren’t seized

 

glad to see you upped the battery cost.

 

How often do you change oil?

 

I think Jerry is probably right that you're driving further on a tank than you think you are and that's why your calculations are so low. Miles are not added to the odometer when you drive without the combination meter working.

 

Thanks for the verification. I had assumed that the storage of the miles driven was dependent on the CM.

 

I can't think of stronger evidence that the odometer DOES NOT work when the dash is out. If it did work, your mileage would be the same. Also, I would pay heed to @Texas Hybrid Batteries comment. He fixes CMs so should know more than either of us about how they work.

 

No. Fix your combination meter first, then look at other things, if there is still problem. Even then, I would wait until the tires were worn out before changing them. Just get the best LRR you can justify at that point. It would not be cost effective to change out the tires just because they are not LRR.

Let me repeat that.

I can't think of stronger evidence that the odometer DOES NOT work when the dash is out. If it did work, your mileage would be the same. Also, I would pay heed to Texas Hybrid Batteries comment. He fixes CMs so should know more than either of us about how they work.