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Old 08-18-07, 10:41 AM   #1
phantomcow2
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If I totally blocked off my grill

Should I expect my engine to overheat? As it is, my thermostat has never gotten above 35-40% of it's travel. I guess since I drive for efficiency, it really wouldn't get that hot. I blocked off about 30% of my grill this morning and took it for a 15 mile spin - no change in the thermostat that I could visually detect.
I am thinking about completely blocking it off, but that means no direct air flow to the radiator what so ever.

My initial thoughts are that if I do this my engine temperature will rise slightly of course. But, that's my aim. I want the engine to warm up faster and stay a little hotter for more fuel efficiency. Plus there should be a bit of an aero advantage. I think that it won't overheat assuming I don't go race it. I think that manufacturers include grills because of liability. They don't know what the end driver will be like, or what he/she will use it for. So, they want to prepare for the worse. But for ME, who never has the engine above 3k rpm, I suspect it won't be an issue. I want to prepare for the winter by doing all that is possible to reduce fuel efficiency decrease.

But I thought I would get other peoples opinions on this as well.
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Old 08-18-07, 10:45 AM   #2
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You may need to add a secondary electric fan and ducting to route air to the radiator. That Aluminum engine won't have the temperature tolerance a steel block does, nor will the Aluminum heads, so you'll be risking warping your heads. Personally, I don't recommend blocking the grill, because the aerodynamic advantage will be minimal, and the only time you'd actually see an advantage in cold weather would be in the -15F and lower range where your cars ability to even warm up enough for heat will be seriously compromised.
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Old 08-18-07, 10:46 AM   #3
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I doubt it, since most cooling does not come from the grill.
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Old 08-18-07, 10:48 AM   #4
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This car mod sounds a little risky to me. Ive never heard of it being done for practical purposes.
Definitely research this more. There are other things you can do to increase efficiency like maybe
getting high quality spark plugs.
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Old 08-18-07, 11:02 AM   #5
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Well, they do on http://www.gassavers.org

SOme of these guys are going 200% above EPA estimates. Most people who block their grill and get a pan to cover the undercarriage of their car (or at least the front) are reporting ~5% gains in FE. For me that would put me just at 40mpg.

When the thermostat gives a reading, where is it actually taking the temperature from?
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Old 08-18-07, 11:04 AM   #6
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This car mod sounds a little risky to me. Ive never heard of it being done for practical purposes.
Definitely research this more. There are other things you can do to increase efficiency like maybe
getting high quality spark plugs.
I believe that I have done what I can do when it comes to mechanical modifications increasing fuel economy. It's time to tackle aero obstacles
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Old 08-18-07, 11:04 AM   #7
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Well, they do on http://www.gassavers.org

SOme of these guys are going 200% above EPA estimates. Most people who block their grill and get a pan to cover the undercarriage of their car (or at least the front) are reporting ~5% gains in FE. For me that would put me just at 40mpg.

When the thermostat gives a reading, where is it actually taking the temperature from?
Generally the return water to the radiator just before it exits the block back to the radiator. You could also increase your cooling capacity by adding an external Oil Cooler. That will help if you go to a reduced flow situation.
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Old 08-18-07, 11:09 AM   #8
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I believe that I have done what I can do when it comes to mechanical modifications increasing fuel economy. It's time to tackle aero obstacles
Time for a chop & channel, along with a full shave and flush mount job.
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Old 08-18-07, 11:16 AM   #9
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When the thermostat gives a reading, where is it actually taking the temperature from?

Consider that the OEM water temp gauges on most modern cars are damped so they point to the same spot when the engine is warmed up, even though the coolant temperature will vary slightly in operation. They're pretty much worthless for reading small changes in coolant temperature.

You might look into installing an aftermarket digital temp indicator that provides real time data.
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Old 08-18-07, 11:48 AM   #10
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Will your car have proper cooling when at altitude (where thinner air has lower heat capacity), carrying friends (or perhaps a trunk full of college books... those physics books sure can be heavy) on a hot day up a sustained grade, when your cooling demands are at their greatest? Economy is great and all, but what are the MAXIMUM cooling needs you'll need? Will you have that covered?
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Old 08-18-07, 12:15 PM   #11
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Seems to me that blocking the grill would decrease aerodynamics. At the moment, the frontal air now flows through the engine compartment and while there is some drag associated with that, at least the air is flowing.

If you block the thing completely, you're putting a big wall up there you have to push through the air. I suspect that the engineers who designed the car designed it for air to flow through rather than have a flat, impenetrable wall leading your vehicle.

That said, a couple of other considerations. You took it for a spin this morning, but it was pretty cool up here (New England) this morning. Even running the car normally with 90*+ heat could have an adverse impact. Also, do you have air conditioning/ If so, you have an AC radiator up there to dissipate heat, too.

Finally, since I have a diesel, I do use a "winter front" to help keep the engine warm in the winter. Much more important for a diesel, or "heat engine". Much abot 65-70* and I really see a spike in my temp. The front blocks probably 60% with the vents open and I can close it down in increments to pretty much 100%, but I only do that on the very coldest of days.

Obviously, since a gas engine provides its own heat (the spark from a spark plug), this is an imperfect analogy at best, so it's just to show you that blocking the front will have an effect and if you're not careful, could be too much of one for your engine, no matter how much you baby it.
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Old 08-18-07, 01:56 PM   #12
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Keep in mind any extra heat will have to be counteracted by more fuel to ward off preignition (detonation). Heat is also the enemy of all moving and electronic components. I blocked off my grill for 200 mph runs down the George Bush tollway one time, and the temperature spiked after the first run, although I did get an extra 8mph on the top end.
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Old 08-18-07, 02:04 PM   #13
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i doubt blocking the grille is really blocking much if any airflow to your radiator. your cooling fan pulls air through your radiator and there is probably plenty of air coming up from under your bumper.
try blocking off a small portion of the actual radiator...a small portion. that will do it
careful attaching it though. you don't wanna hurt the core of your radiator or you'll be replacing it.

you really need to be able to monitor your temp. accurately and i bet the factory gauge isn't that. you also should know what temp it is really running at so you probably need an aftermarket gauge.
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Old 08-18-07, 02:06 PM   #14
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I could be wrong about this, so if I am, feel free to correct me, but I think the radiator thermostat switches the fan on and off. It could be right now your fan only has to run 50% of the time to keep a constant temperature, so if you block off part of the radiator, it may be running 80% of the time now with no change in temperature. This will be fine and you can keep blocking more of the radiator and you won't notice anything until the fan has to run 100% of the time and can't keep up, then your engine will suddenly overheat.

Again, this may be totally off base, but that's how I thought it worked.
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Old 08-18-07, 02:11 PM   #15
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Keep in mind any extra heat will have to be counteracted by more fuel to ward off preignition (detonation). Heat is also the enemy of all moving and electronic components. I blocked off my grill for 200 mph runs down the George Bush tollway one time, and the temperature spiked after the first run, although I did get an extra 8mph on the top end.
Did you say 200MPH? Sweet! Fastest I've EVER hit was 181 in a highly modded '69 Cougar. (429 Super Cobrajet under the hood w/ Dual 1150 Strip Dominator Holleys, .488 Torquer cam and a nice little 4500 cfm Rochester Supercharger, wide ratio 5 speed/OD transmission).
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Old 08-18-07, 03:02 PM   #16
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Did you say 200MPH? Sweet! Fastest I've EVER hit was 181 in a highly modded '69 Cougar. (429 Super Cobrajet under the hood w/ Dual 1150 Strip Dominator Holleys, .488 Torquer cam and a nice little 4500 cfm Rochester Supercharger, wide ratio 5 speed/OD transmission).
-Dallas Street Races back when I had even less common sense. Mine was a single Schweitzer turbo setup on a former World Challenge 1LE Camaro. Most of the others were modded Vettes, Vipers, and a bunch of Callaway Twin Turbos. Used to make my car payments + upgrades out there.
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Old 08-18-07, 03:14 PM   #17
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Well, I blocked off about 80%. All that's left to do is wait. By the way, headers DEFINITELY gave me a little FE. I can't say exactly how much, but I am noticing an improved trend for the past 2 weeks that they've been on.
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Old 08-18-07, 03:31 PM   #18
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Back in the day....I used to block half of the grill on my '69 Nova. It was a
250ci. six and we used to go on weekly ski trips through-out western and
upstate New York all winter. Sometimes the heater just didn't keep us very
warm, soooo I kinda helped things out by blocking some of the cold (frigid)
air from the radiator.

I would assume that 40 years of automotive engineering has made this practice
a thing of the past.
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Old 08-18-07, 03:32 PM   #19
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I could be wrong about this, so if I am, feel free to correct me, but I think the radiator thermostat switches the fan on and off. It could be right now your fan only has to run 50% of the time to keep a constant temperature, so if you block off part of the radiator, it may be running 80% of the time now with no change in temperature. This will be fine and you can keep blocking more of the radiator and you won't notice anything until the fan has to run 100% of the time and can't keep up, then your engine will suddenly overheat.

Again, this may be totally off base, but that's how I thought it worked.
The thermostat is a mechanical restrictor in the water flow-path; typically in the head. The only function the thermostat should have is for cold engines. It completely blocks off flow out of the engine to the radiator until the water's temperature is up to proper operating temperatures. By limiting this flow, the engine warms up faster. Then typically around 160F, the thermostat starts opening and by 180F, it's fully open. The variable-opening of the thermostat allows the engine to operate at a fixed temperature regardless of the outside air-temperatures (and thus the radiator's heat-shedding capacity). Engines typically operate with water-temps around 200F.

The thermoswitch is an on/off binary switch that's installed in the radiator and controls the auxilliary radiator fan. Modern cars and those with laterally-placed engines, like the OP's Civic, typically have two fans. One that's on all the time and one that's controleld by the thermoswitch. When temps get around 210F or above, the thermoswitch closes and turns on the 2nd fan. Some thermoswitches have two contacts and can run the fan at two speeds, low & high depending upon actual water temps. The off temperature is also independent and is usually around 180F so that you don't end up with a continuous on/off cycling of the fan as temps drop through the initial ON temperature.

Finally, the thermosensor drives the dash gauge. This is typically is an analogue sensor that varies its resistance based upon temperature and has a negative temperature coefficient. That is, was temperatures increase, the resistance through the sensor decreases. A voltage is applied to the sensor and the sensor's resistance is detected and used to drive the dash-gauge. Some ECUs also use the temperature to compensate air-fuel mixtures for changes in air-density as the hotter engine will heat up the incoming air more and reduce its density.


As far as the OP's car is concerned, go ahead and try blocking off the grill. As JSchen mentioned, you should design the measurable parameters of the experiment to gather actual quantitive data over a wide range of driving conditions. Always test the worse-case scenario to find the envelope of performance required.
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Old 08-18-07, 03:35 PM   #20
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i doubt blocking the grille is really blocking much if any airflow to your radiator. your cooling fan pulls air through your radiator and there is probably plenty of air coming up from under your bumper.
try blocking off a small portion of the actual radiator...a small portion. that will do it
careful attaching it though. you don't wanna hurt the core of your radiator or you'll be replacing it.

you really need to be able to monitor your temp. accurately and i bet the factory gauge isn't that. you also should know what temp it is really running at so you probably need an aftermarket gauge.

+1 check that clear space in front of the actual radiator and crawl underneath to check out the open space. My pick up has plenty of open space from undearneath. Closing off the grill would accomplish squat.
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Old 08-18-07, 03:48 PM   #21
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Where I am, it isn't too mountainous. We have hills, but nothing major at all. If I travel north 60 miles, you get into the white mountains, a whole 'nother story. I made the grill block out of sheet metal, and it slips into little slots I ground with my dremel. So if I find my engine getting too hot for my own comfort, I can easily remove them.
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Old 08-18-07, 04:02 PM   #22
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I'd block off the grill when I lived in North Pole, AK but temps were in the sub-zero range for several months.
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Old 08-18-07, 04:04 PM   #23
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It looks like I am not alone in my thinking. It makes sense that racing cars would be concerned about aerodynamics, as it can reduce the load on the engine and accelerate you quicker.


Notice the partial grill block, the front air dam, and there is probably a cover for the undercarriage.
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Old 08-18-07, 07:24 PM   #24
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Thanks for clarifying, Danno.
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Old 08-18-07, 07:44 PM   #25
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You should definitely at least get the Moon discs, because those look cool on damn near anything.
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