MPG suddenly dropped this week.

After putting air in the tires, reset the TPMS under the steering wheel. I'd also say raise those tire pressures to 38/36 to start. If the ride is compliant enough for you, go to 40/38. You get better mileage with a little more air pressure than what's displayed on the door.

 

Temperatures are dropping.

That means PSI will naturally be lower. Tires soften with the cold. So as you noticed, they'll need to be topped off. 33 is the minimum. I've been running at the maximum of 44 for many years now.

That also means engine warm-up will take longer, which most definitely affects efficiency. The seasonal MPG drop is something you get use to with Prius ownership. It certainly makes the arrival of spring very exciting. I know that well, living in Minnesota.

Make sure to take advantage of ECO mode. It causes the engine to shut off sooner and stay off longer than with the Normal or Power modes by altering thermostat tolerances with respect to coolant temperature... which is tied directly to both the emission-system and the cabin heater.

 

Have you got the 15" or 17" wheels. We have the 17", and I keep them around 38 psi. With the 15" a lot of folks are setting them around 40~44 psi range.

If your tpms didn't go off at 28 it likely needs to be reset; it's currently set to too low of a threshold. The procedure's in the Owners Manual. If you really want to set the tpms on a hair-trigger: temporarily set your tire pressures about 10% higher than final, reset the tpms, then bleed air to final pressure.

There's a second possibility, that the tpms system is defective. You could test that by purposely running pressure down low on at least one tire, and see if it activates. I believe the threshold is roughly a 25% pressure drop.

For mileage tracking, it'll take a few tankfuls before things settle down. Do bear in mind:

1. Toyota's in-dash display of mileage is notoriously "optimistic".
2. A car that's still on it's first tankful is still dealing with the vagaries of it's time at the dealership, likely long idle periods, partial fill ups and so on.

BTW, check your temporary spare pressure too. Want to be it's not at the spec'd. 60 PSI?

 

Colder weather hurts in many ways. If you are using cabin heat, that adds even more fuel consumption, beyond the low tires and increased engine warmup and engine heat loss.

Possible other factors include the seasonal changeover to winter fuel blends, and increased precipitation causing drag on the road.

 

Are there any cheap TPMS pressure readers that anyone is aware of, that can display the pressure readings from the 4 sensors?

 

Use this one every two months:

12 Volt, 100 PSI High Volume Air Compressor

This one might be a little slower but it is cheaper:

12V Air Compressor - 250 PSI, Compact Air Compressor

Bob Wilson

 

It's not at all risky to run them up higher, say 40 all around, then if you find it too rough bleed a bit off. I settled on the 36~38 zone, seemed a decent compromise. I agree the 17's ride is a little harder. Speed bumps are the test, what you can tolerate. I hate those things...

 

I agree with the general conclusion of ambient temperatures factor. I also learned during more than one year of being Prius driver that air condition and cabin heating plays very significant role. Hence now - whether outside becomes cold I use the heating only at minimum just to avoid steamy windows. At least we usually are dressed for appropriate season. Below is another discussion related to MPG vs ambient conditions:
starting engine temp vs ambient temp re: winter MPG | PriusChat

 

Too lazy to use either for a pressure check

My understanding (perhaps incorrect) is that the TPMS sensors already have that info, hence my query as to a way to simply read those readings while seated in the car. Any way I can get to these from the Nav display?

 

I would especially like the ease of getting these off of a scanner/reader since the Prius tire pressures seem to vary quite a bit with the outside air temperature.

Also, in this respect, would Nitrogen be less susceptible to outside air temperature variations?

 

minVCI appears to read the tire pressures.

Bob Wilson

 

I am running 42/40 without any trouble not sure if I can tell much of difference the roads are here just simply terrible.

 

You already have Nitrogen (mostly) in your tire it would make NO difference .

 

Because all 4 tires were near the same pressure the tpms didn't care, btw, much better mpg's at 40ish then 30ish

Yes nitrogen will require less maintenance, instead of refilling the missing air once a month it's 6-12 month's, but unfortunately, nitrogen is the "N" word on this forum

As the temp get's below the 70's the mpg's drop, fast.

 

I have torque ...

Is possible to get the PID number ?? for the TPMS sensors ?? Then perhaps torque can read it it would be usefull

On the pressure gauge I got this on sale and really like it.

Code:

http://www.amazon.com/AmazonBasics-Programmable-Digital-Tire-Gauge/dp/B005PJJ89U/ref=lp_15709131_1_7?s=automotive&ie=UTF8&qid=1382125253&sr=1-7

 

Simple rule is 1PSI per 10F so I hope you allowed for cold mornings between now and your next pressure check.
Better high than low.

 

Out side temps go down ... MPG goes down ... Time for grill blocking

 

My mpg just went down also from 46 to 42. But what I want to know is, how do you get the car warmed up to defrost window and defog inside windshield? I am used to a remote start to get car nice and toasty and no scrapping. Will I just have to get in and sit for 10 minutes waiting for car to warm up?

I live in Oklahoma so it does not get to cold but we do have some cold snaps in the teens.