Grill blocking in mild winter temps

Not many. I never even noticed lower mpg in winter during the 4 winters I had a Prius.

 

It's somewhat helpful; I see similar temperatures in the winter. It especially helps while it's first warming up. I bought two lengths of pipe insulation, and use it to block 75% of the lower grill (3 of 4 openings), and 50% of the upper (one short piece on each side) during the coolest part of the winter. It doesn't take much savings to recoup the $1.98 investment. I've been doing this since shortly into my first winter with the car, so I can't give you an amount - but I'd estimate probably 1 or maybe 2 mpg.

My summers are milder than yours, so I leave in 50% of the lower grill blocking year-round (with a ScanGauge to monitor temps). It does make a much bigger difference in colder states, where they have trouble getting the car up to and keeping it at the normal operating temperature.

One way you can tell some of the potential savings - how far from your starting point are you when the engine first turns off (generally, this is at 40°C)? The difference between your answer for summer versus winter is an indication of what could be saved. Not all of it will be, but maybe half or so. You'll also save more by reaching 70°C sooner, especially if you use pulse and glide - before 70°C, it's very hard to get much benefit from P&G, because the engine is often still running during your glide.

 

It does really help at warming faster and staying warmer

 

Like Mac said, it can help at any temperature but the degree to which it helps is highly dependent on how cold it actually gets. I think if someone has a morning commute (especially before the sun is up) at temps even in the 40's and 50's grill blocking is definitely still worth doing...takes virtually no money or time.

 

Try it. It is $2 for the pipe insulation.

 

Note that it helps warm-up, so you get the best squish for your 2 bucks on shorter trips.

 

It's 1/2 inch.

And yes, I think Ken's guide is a great guideline to go by. But for someone not using a scangauge or Torque you would want to stay on the conservative side of that and use some common sense. But I also think there is room to be a little more aggressive if someone is willing to monitor things with the above mentioned tools.

 

What is FWT? And yep grill blocking definitely helps, short trips more than long ones.

 

On Torque I keep 6 different gauges up:
3 for different temps (engine coolant, batt temp, inverter coolant) and 3 for electrical flow (amperage in/out of battery, SOC, AC watt usage)

 

Coolant temp is OK but that is mostly influenced by Outside Air Temp. Inverter temp or Inverter Coolant temp is mostly dependent on the use of the inverter. If you are on EV a lot then that temp will really climb compared to coolant temp. As a baseline inverter temp runs OAT + 20F.

 

As Jim says just watch coolant temp and inverter temp if you are blocking anything on the top.

Torque is an app for Android phones. The setup is a fraction of the cost of SG and much more flexible with far more possibilities than SG.

In fact, to anyone really considering a SG that currently doesn't own any Android equipment I would recommend just getting the cheapest Nexus 7 tablet to use Torque on. Cost will be in a similar ballpark and you have a sweet tablet to use as well.

 

Just as a reference for someone who just did it this past weekend, it warmed up here this week and has been in the mid 50's going to work in the morning. I have gotten the best morning mpg the past 3 mornings with the lower grill blocked 100%.
Part of that is me getting better at driving my Prius, but I couldn't have changed that much 3 days in a row, and I have gotten better the last 3 days in a row.
It's in the low 60's to high 50's driving home at night and I have been getting even better mileage going home.
I cannot compare to some people on this forum, but getting 58.6 mpg for me on my short 10 mile commute is awesome.