Buying a used prime - MPG on dash is low. Is this a red flag?

it is not a red flag. there are a number of reasons the car may have gotten low mpg's since last reset, and the same goes for high mpg's.
having said that, any car can certainly have an issue, and you would need a test drive to find out.
but reasonable mileage primes are fairly bulletproof in that respect.

 

Many things will impact the MPG dashboard reading. For instance, on a hot summer day my wife prefers to sit in the air conditioned car while I run into the store to grab a few things. I've seen the mileage for a 500 mile trip drop noticeably just from a 20 minute grocery shopping trip that included using the AC.

 

I'm totally confused. Are you talking about:

1. miles on the odometer (my first hunch)
2. current miles per gallon (aka mpg) showing on the dash
3. ambient temperature, in Fahfrenheit (aka F)

 

I have seen threads where the OP was complaining their mileage was low.

When dealing with a dealership mechanic they need a code to chase. Without a code they have no idea what to do and will say your car is fine.

It could be something simple like a clogged air filter or low tire pressure.

 

I wouldn't say it's a red flag if you're browsing listings online but if it's used you'll want to make sure to have your own independent mechanic give it a once over (legit dealerships won't have any problem with this request).

Likely the reason for low MPG on the dash is the dealership is only moving the car occasionally for short trips around the lot/showroom/service/test drives and not recharging the EV battery so the ICE is running more often and probably reset the lifetime MPG counter on the ODO in some way - probably replacing an old 12v aux battery.

 

I haven't seen a dealership yet plug-in a PHEV; they treat them like gasoline cars. The engine is always running to recharge the traction battery, so the car can start. That really drives down the mpg. If you sit in the car, you can toggle trip-a, trip-b and lifetime mpg - but know that lifetime mpg will be reset when they change the aux. battery w/o plugging in a car settings saver. Those units save car settings by keeping a constant 12VDC on the system, while the battery is being swapped out. The car won't have to relearn everything.
An EV only car, they have not choice but to plug them in; otherwise there won't be any test drives. Just a very expensive driveway ordainment.

 

^ That.

At dealerships it's normal for the cars to have dying/dead 12v batteries until an hour before the customer wants to see the car. And they move the car with a jumpstart 12 times a month, about 200 feet each move.

So you're seeing something that was reset recently and left about the worst possible MPG record on the dash computer, and it's not the kind of thing used car dealers are going to stop doing any time soon.

One of those things that you need to learn to see through in order to enjoy used-car savings.

 

Here’s my tale of two used primes

2017 prime w 19k miles and 199.99mpg lifetime when I bought it used in 2019. Obviously driven exclusively in EV mode. The traction battery is seriously degraded now today in 2024 and charges to less than 20 miles of ev only driving. It now has 140k miles.


2020 prime w 109k miles and 48.9mpg lifetime when I bought it used in 2022. It obviously was never plugged in. So, its’ traction battery is very healthy and charges to 24 miles of ev driving now today in 2024. It now has 145k miles.

overall I prefer the 2020 bc it has five seats vs four in the 2017. And, I would encourage those who want a healthier battery to seek out a low lifetime mpg used prime. Those who want a healthier engine should seek out a higher mpg used prime.

 

I've occasionally advocated plug-in owners should purposely drive it like a regular hybrid, say once a week. For the benefit of the engine.

It occurs to me, with the very low usage on our '10, that's about what we're doing, driving it about once a week.

And we're big on errand consolidation: yesterday had a grad ceremony to drive to, and beforehand did a grocery run.

 

Just to clarify; yes the 2017-2022 Prius prime absolutely 100% does calculate the car’s lifetime mpg, along with the car’s odometer. Both the mpg and obviously how many miles on the car both survive a dead and/or replaced 12v battery. As others have suggested, toggling through the trip button on the steering wheel gets you to the odometer.