2010 Prius Grill Blocking strategy

This may turn out to be the main advantage of grill blocking (second would be keeping the block warm during stops - good for shopping trips).

 

I saw this grille blocker on a Civic.

 

I've got approx. 85% lower, 45% upper blocking, and I'm not seeing much difference except in the first few miles, and some improvement with the cabin heat. Is anyone still experimenting with this or are we still basing everything on the Gen II chart?

 

I had had mine (lower grill 100%; upper open) blocked and unblocked a couple of times when the weather was cold. I checked temperatures at a couple of places along my normal route. The car didn't seem to warm up any faster but it did stay warm longer after it was shut down. I also noticed about a 5 or 6 degree increase in temperature while driving on the highway (not needed) while blocked.

I did not check mileage differences and what I saw was with only the lower grill blocked. If/when it gets cold again I'll try it with the upper grill blocked as Ken and Dave suggest and see what that does.

 

the lower the speed driven, the higher the grill blocking benefit. if temps in your area are 40's or less, i would do 100% top and bottom.

on my 2010, i blocked all bottom, left one slot open on top...

2006,. 100% top and bottom

for differences, check out this thread with and without blocking

http://priuschat.com/forums/gen-ii-prius-fuel-economy/74347-another-grill-blocking-thread.html

 

Yeah, I see a difference there too. But highway mpg seems unchanged.

I added a little more blocking up top (80%?), and may have seen a small improvement in mpg but it's too soon to tell. I might close off the bottom a little bit more, although I'm still leery of doing 100% on the highway without a Scanguage.

 

The scan gauge gives me a bit more confidence because it does a good job of monitoring ICE coolant temperature, unfortunately no one has the codes yet to monitor the inverter coolant temperature. Adrianblack and others are working on getting all the codes they can and we now have a way to turn off the backup and seatbelt beepers ourselves. Being able to monitor the high Voltage battery Amperage is also nice.

 

Tom i am guessing by your location that anything above 40º right now is a pretty rare occurrence. i would not hesitate a second if you have temps that do not rise above 45º to block everything.

some air will still sneak in, and the Pri does not need much to cool off. i have used scangauge and this weekend did a 35 mile jaunt down the freeway with temps at 58º... temps bumped 202º a few times, but that was about it. for me, i start removing blocks at 50... but 100% below that

 

TEST A - 53.6 MPG @70 mph


TEST B - 51.6 MPG @70 mph


TEST C - 53.3 MPG @70 mph


Protocol and test conditions

• 57F (14C), dry pavement, humid
• two runs, West and East, south wind at ~10 mph
• I-565 Jordan Lane Huntsville AL to Mooresville AL
• cruise control maintained speed, GPS calibrated
• +13 miles each leg, added together for total performance
• 2010 Prius (VZW30), 8,500 miles ODO, OEM tires, 45 psi
• ICE and transmission oil changed at 5,000 miles
• Shell 87, E10
• Warmed up at least 20 minutes before first run
• Disposable, cardboard shields held with duct tape

Bob Wilson

 

Thanks - was wondering about that. And for longer highway trips in 20-30F, do you think 100% blocking (lower AND upper) is still safe? (I have a long trip coming up in a few weeks)

 

What is the maximum temperature the coolant gets to, before a warning light in the car goes on? I can monitor the temperarture with the obdkey I now use. I'd like to know the max temp I should stay away from.

 

oh ya. i think you will see that at freeway speeds even, your car will not go above about 185º and will bump down to 175º occasionally which basically means your radiator is running closed most of the time if not blocking.

without scangauge you will not see this, but when the Pri is running radiator open or near wide open, the temp says pretty static at 190 give or take a few degrees. when its dipping down that is because the radiator is closing stopping the circulation. the cold air creates a spot on the radiator that accounts for the temp drops. then the radiator opens again, water circulates and that accounts for the spikes.

this is not what you want.

with grill blocking, i see temps running from 185 (ya even with grill blocking with temps below freezing your Pri will still struggle to keep warm) to 200-205. the 200's i only see when temps start hitting about the upper 40's.

last year in SPM, i did a 150 mile trip with temps in upper 20's and low 30's. 100% grill block top and bottom. water temps pretty much stayed in the low 180's...iow, thermostat mostly closed.

 

i have seen spikes to 207º... no alarm, but did get the fan to run after car was shut off. i wish i had after long run on freeway and going to street speeds. but that was summer time. checked temps to see when it came on cause it turned on about a minute after car was shut down so assuming temp spiked higher than the 207

 

Thanks! :thumb: I was wondering exactly what it would take to keep the engine warm enough at highway speeds, and it seems like the blocking has to be near 100% to make a difference.

I'm going to go 100% bottom and leave the top at 80-85% (since I don't have a Scanguage) - hopefully that picks things up a bit. 44mpg would be a major improvement over the 39mpg I saw on my last cold highway trip.

 

Well, I did 100% bottom, 95% upper block today and took a little highway trip in 20F - and the "outside temp" indicator swung by 10F after about 20min, but the mileage didn't improve. In fact, mileage seemed to drop a bit (.2mpg) at that point.

So I'm going back to 75% bottom and 80% upper for highway - but I would really REALLY love to know why the mpg drops so much on cold highway trips.

 

What were the road conditions? Any wind? What kind of tires/pressure? Did you have a load?

 

No load, moderate wind, snow tires at 39/37, same road I have done other trips on so it's all relative - the only different variable was the air temp.

 

You really need to do an "A" "B" "A" test running the same vehicle; two opposite direction passes of at least 10 miles; changing only the grill blocking. A single pass doesn't provide enough data because too many variables can change.

It is a combination of factors but at highway speeds:

1. air density - increases aerodynamic drag
2. cooler tire rubber - increases rolling drag
3. pushing ICE into less efficient regions - more a problem for the 1.5L Prius, the higher drag at a given speed puts the car in less efficient ICE operating regions. HINT: reduce top speed by ~5 mph for every ~10F drop in temperature below 50F. Drive the MPG instead of mph.

Once the car is travelling faster than 46 mph, the 1.8L ICE will be running all the time, 42 mph with the 1.5L Prius. There will be excess heat so it becomes a question of drag vs. operating the ICE in an efficient speed range.

Bob Wilson

 

It was a round-trip (one I have done before) and I saw the same thing on both legs. My max speed was 69mph (about half the trip), and about 1/4th of the trip was at 64mph. (the rest was below 50, and mpg was still not great)

I have difficulty accepting the first two as explaining the entire loss in cold temps without some numbers backing it up. (#3 is pretty much irrelevant to the Gen III.) I have seen figures for aerodynamic resistance, which is a noticable increase relative to itself, but what exactly is the affect on mileage? And for the tires, are there any numbers/stats at all to look at? And would it be better to run higher psi or lower psi in cold temps to compensate?

 

Hi Tom,

Part of good science is learning how to control the variables in an experiment. That was why I tried to suggest a tighter protocol, two-way runs over the same course of at least 10 miles. But there are no doubt other approaches.

On the effects of air density on aerodynamic drag, I would recommend some background reading:

• Wiki air density - air density is linear with temperature
• Wiki drag coefficient - force is linear with air density and velocity squared times a constant
• Wiki power - includes the definition of work as force over distance

As a practical exercise, I ran a highway trip at 65 mph to South Carolina two years ago and the MPG per segment varied in direct proportion to the air density as a function of air temperature. The warmest segment was 35-40F and the coldest 15-20F. It was a practical example of physics at work.

I went back and checked my sources but it appears the problem has more to do with cold temperatures causing the tire pressure to decrease and thus increasing the drag. Usually we lose a little more than 1 psi per month but when the temperatures cool, the tire pressure can decrease even faster making them relatively under inflated. It is likely to be more a problem of tire pressure maintenance when the temperatures cool.

Bob Wilson