Can anyone quantify the effects of winter grill blocking on engine water temps/cabin heat and mpg.

That test won’t really show the real benefits of grill blocking. If the car is just parked engine passive cooling is just a same as parking it after drive. Idea of the grill block is mainly to reduce the passive cooling to engine block (and other pars) at speed.

With no grill blocked engine temperature difference to outside temperature half at maybe a bit less than an hour. With full grill block that might be slowed down to maybe one and half hours. So for example if engine is 70c and outside temperature is -30c after that time engine is cooled down to 20c. At the same time heater use can lose many degrees of Celsius per minute. So heater is the main cooler of engine.

Grill blocking while driving has the main benefit of engine reaching higher operating temperatures. For example if the engine temperature would reach 70c without grill block and 84c with grill block and engine would be started at 62c you will have a lot longer time before engine is turned on for heat.

I don’t have any accurate date. I haven’t really seen the need for the data. The benefits are easy to proof and with almost no negative effects or cost I see no reason not to (partially depending on temperature) block your grill when you’re not using your AC for cooling.

But yes heater use has huge effect in fuel economy on gen 2 Prius. Normally I use the heater on lowest temp setting 16c and lowest fan speed. You won’t really need any warmer than that while driving.

 

Perhaps @Mendel Leisk has some insights. I believe he uses grill blocking in addition to year round engine block heater, IIRC..

 

You can clearly see that many people do block the grills on their regular cars just for the engine to stay warmer. And it does help even if they have good/new thermostat.
And as the gen 2 Prius will start its engine just to produce heat you can clearly tell that it does help.

Because blocking the grill in gen 2 Prius will increase engine temperature you can tell that the effect of reduced drag reduction is less than effect of less airflow around engine. If it wasn’t grill blocking would cool the engine.

 

CAUTION:

This discussion is NOT for Gen 4 Prius that already have active grill shutters fulfilling this purpose.

Some people like me browse the different forums so I posted this disclaimer.

 

i don't recall any scientific studies being done, but i have to agree with valde, it would only help at speed, the faster the better, and i would think that done correctly, it would improve aero, not reduce it.

 

I'm not sure, but I don't think the foam tubing style of grill blocking would help with aerodynamics, or not much.

 

no testing on that either.

fwiw (not much) i can't see a noticeable improvement in mpg with grille blocking. or increased tire pressure for that matter. it would probably take controlled testing over long distances.

 

Grill blocking will help aerodynamics regardless of how it’s done. That’s because aerodynamics of the outside of car are always better than aerodynamics in the engine bay. Texture on the surface of blunt front end isn’t really that important.

 

I've only got 50% block lower too, any effect basically lost in the noise I think.

 

This winter I was doing my commute without a grill block (was installing LED driving lights behind my grill to come on with my brights, so had them out). When removed I noticed about a 2mpg loss and regained about 2mpg when I put the grill block back. My commute is 35 miles each way, 95% highway done at ~75mph. I use the pipe insulators cut in half and have 100% top grill block (except LEDs) and 50% bottom. Watching my scanguage, the car does seem to come up to temp faster, and requires just a touch less rpm to maintain speed on the highway. I do 42-44mpg going to work and 50-55mpg (in normal conditions - wind, rain, very cold, etc and these drop) coming home on my winter tires at 42-44psi .

So doing the math, a grill block seems to provide a ~4% increase in fuel economy on a highway commute. I think it's a combination of allowing the car to get up operating temp faster, better aerodynamics, and slightly warmer air reducing engine pumping losses.

 

Here's what I've done each winter for the past several years:

…and yes, I use the same pieces each year (I hate waste!) The ICE warms up much quicker, the interior of the car gets nice and toasty within about ½ mile, and the gas mileage goes down as it usually does in the winter (as the formula changes with the seasons) - the overall gas mileage doesn't change much (see my fuelly figures), part of which might be explained by using the Hybrid Automotive Prolong Charging System (I bought mine back in Jan 2014) - but, as they always say, YMMV!

 

For that 2c heat lost per minute while stationary most of is due to heater use. And for the part that’s not effect of the grill block is still small. Like I said earlier main benefit is for the engine to reach higher temperatures when driving which then means that it will stay off longer before it needs to start to provide heat.

Probably the best way to test is to test higher speed (where engine is on all the time) fuel economy with fully warm engine. That way you can test only the aerodynamic drag reduction benefits of grill block. Then compare that to normal drive with cold start.
But doing fuel economy tests on normal roads is hard. And you should you should think about the margin of error.

If fuel economy improvement is better on normal drive with cold start then that proves that the heat loss reduction has more effect that aerodynamic drag reduction.

 

The site ecomodder is a good resource for your discussion with him. The purpose of grill blocking is two fold - first is to reduce drag on the car, and second is to give you a faster warm up time. The engine bay of a car is much like a parachute in reverse; it's a large concave area that traps a lot of air and does not easily let air escape. Similar areas on a car are the wheel wells. Running the heat in a Prius will be more detrimental to efficiency because the engine will need to run more, but the energy used to actually circulate the heated engine coolant is negligible because the water pump is running any time the engine is turning. In a Prius, the loss of efficiency is more from running the engine rather than running the heat. If the engine is already running, as it does with highway driving, then running the heat will be inconsequential. If the car is sitting parked and running the heat, then yes, the engine is running only to generate heat, and this heat is by definition wasted energy from the engine, the purpose of which is ideally to transport you from one place to another, not to serve as a fireplace to keep you warm.

 

Reading many threads you would think the purpose of a car is a mobile entertainment system.