Blocking Air Intake/winter Driving

Why do you block the top and not the bottom? I am afraid to block the entire grill, but I blocked the bottom, since it is uglier when the top is blocked. Am I the only one with the "bottom only" blocked?

 

That's what I'm going to be working on right now. I fabbed up some pretty thin Aero hubcaps, and it was pretty easy to do, so I'm thinking of making it out of aluminum. I'm going to cover the edges with some kind of rubber trim to protect the paint on the car, and make a clean seal to the car to block air better. I'm also thinking about going to an auto store and buying some of that paint that matches the OEM color so the grille block would blend in better with the car.

I'm thinking about making one for the lower grille as well, but flat black, and with just a small opening in it for the summer time, and still be able to be blocked off by foam in the winter.

 

Can someone provide some technical explanations for this ?
Most contemporary engines have water cooling bypass valves which skip the radiator until the water temp has reached it's optimum, so blocking the grille should not have any effect on the internal combustion engine warming up faster.
I can understand an improvement in terms of aerodynamic drag at freeway speed, but I am surprised that this would offset the loss in battery efficiency resulting from colder temperature.

 

Hi ze_shark,

It really does not offset the decrease in battery efficiency as there is little to no change in battery efficiency with cold temps. Conductors get lower resistance at lower temps. Battery power on the other hand does drop because chemical reactions are greatly effected by temp. And this causes the engine to be used at a high power level, up outside its max efficiency more often.

When a car is cold, any car, its thermostat is closed. Its only getting cooled by conduction through the coolant, and air flow over the engine. Cut down on the air flow through the engine compartment, and the car warms up faster. Ever stick an ungloved hand out of a car window at 10 F and 30 mph ? Although, there is evaporative cooling in that example, its shows the issue.

The thermostat does not open to about 185 F (boiling of water at standard temp and pressure is 212 F). In full hybrid mode the engine is cutting out during low power requirements, and the car runs on battery then. In cold weather, as there is not a stove for heating the passenger compartment, the engine must run when coolant temp is too low to heat the passenger compartment. All the while the air is blowing through the engine compartment. In winter operation with the Prius in city traffic, there is allot of time the engine is off, and its cooling then, just by conduction and winter winds blowing through the radiator.

The Prius was also designed as a min-emissions vehicle. So, it operates differently during warmup, to reduce emissions, than once it is warmed up. This warmup phase runs at about 25 mpg, versus more like 50 afterward. Even in 13 degree weather like my drive home today. After warmup I had 50 mpg straight across the consumption display for 1/2 hour on the highway at 63 mph. The first 5 minutes of warmup was 15, and the second was 35 mpg. Even though that was on slower secondary road travel.

 

Hi Winston,

The top blockage is perfered for aero and rain ingress reasons. But the bottom slit is preferred to be open, as the hybrid system is cooled in the lower third of the radiator. It has no thermostat, they want the transistors as cold as possible.

The engine on the other hand has a thermostat, and will increase the cooling rate if it gets too hot. So, its safer to block off the engine cooling in preference to the inverter cooling.

 

The real short answer is that below ~40f, with the grill open the engine may NEVER get to to 185F, especially in short jaunts, and stop and go driving. Remember, it is a small engine, running very efficiently and not running much of the time. (The longer answer is why does the engine need to be warm to run efficiently,,,asked and answered on other threads)!

Toyota has to design for warm operation, even at the expense of efficiency at lower temps. Grill blocking overcomes this somewhat.

Icarus

 

Can someone post a picture of this "Blocking" Technique? I am very interested. I live in Rochester MN where we stay in the negatives all week and I'm only averaging 28-30 MPG's. Not really what I expected. In fact, I'm kind of disappointed.

 

Your model is especially helped with a block heater. Late in the season, it can also be used in the spring and fall. Our Japanese friends use it year round.

GOOD LUCK!
Bob Wilson

 

its easy to understand your concern, but i block both, have done it for a long time and do it for all driving conditions at 50ºF or below...

here is a situation from this morning about 10 am. driving 35-40 mph...OAT actually about 33ºF (when blocking grill, the temp actually picks up engine heat hence the higher reading) . car sat outside overnight (overnight lows probably not much different...no lower than 30 probably if that). driving in suburban conditions. at time of pic...water temp was 175º but had ranged from 160-185 in last minute or two.

 

oh oh, tried to post pic, did not work... we will try it one more time



*edit*

finally after about 10 tries, got the pic to load...now before i started blocking, i would have been at 15-30 on the first 5, 25-50 on the 2nd 5. so as you can see, a pretty good improvement.