scantools

I suggest ScanGauge. Of the aftermarket devices used by PC members to monitor goings-on under the hood, that seems the most popular by far.

This is a good starting point for learning how it can be used to maximize fuel economy.

 

You can buy the ScanGauge II from a number of places. I bought mine with no problems from the shop that supports this site. Click the "Shop" tab at the top of pages on the PriusChat site and look for ScanGauge.

 

I might have more directly answered your other question. The ScanGauge keeps trip data, but I use mine primarily to monitor my current trip MPG, current MPG, traction (HV) battery current, and RPM. The ScanGauge site will give a full list of the items you can monitor on most cars. If you do a search online, you'll also find codes specific for the Prius. The SGII doesn't directly improve gas mileage but can give you a better indication of what's going on in the car so that you can improve gas mileage.

An extra bonus is the SGII will allow you to dump fault codes from the car in the event you should get one. You can then check these online to get more information on what's wrong with the car.

There are other solutions that require substantial work to install. The SGII just plugs into the diagnostic port. Takes about 10 minutes to mount it with velcro and secure the cable. Someday, I'd like to put together a more intense system that uses the MFD, but that will have to wait until a period in which I have lots of free time.

 

It will show coolant temperature. Other temperatures (MG1, MG2, inverters, battery) are available in the CAN data stream, but I haven't seen where XGauge users have configured theirs to read any of them except battery temp. That's not an issue with grille blocking, but inverter temps are. I suggest keeping the lowermost slit of the grille unblocked until winter to help with inverter cooling.