3 MPG GAIN WITH GRILL COVERS

[Chinto]

I read that too but the facts don't seam to support it. At 70mph the ICE will get up to opperating temp and any gains after that have too be aero and I saw 4.5mpg at many different temps.

 

Are you referring to engine temperatures or outside temperatures?  It seems that the shutter system performs poorly in cold weather temps as evidenced by the gains made by simply obstructing air flow through the grill and increasing the engine temperature to optimum.   It seems that optimum engine temperature trumps aerodynamics in attaining optimum mpg at 32 degrees and below outside temps.   

Edited January 4, 2013 by Chinto

[bymaine]

Don't forget to remove the foam inserts before a carwash......

[Chinto]

Don't forget to remove the foam inserts before a carwash......

 

 

Actually I had my car washed yesterday with the foam inserts in place and had no affect on them.  

[plus 3 golfer]

This is what Ford says about the active shutters. 

 

The standard Active Grille Shutters on the C-MAX help to reduce air resistance and increase fuel efficiency. When the Active Grille Shutters are fully closed, vehicle aerodynamics are improved by roughly 5 percent.

 

So if the C-MAX has a C_d = 0.30, the shutters reduce the coefficient to 0.285.  This will equate to roughly a 3.3% improvement in FE at 70 mph all other things being equal (assume reasonable values for frontal area and rolling resistance).   So, from the graph the MPGs at 70 mph at 63*F are about 41 and 44 or a difference of 3 MPG.  That's about a 7.3% difference over 2X what I would expect from the shutters alone per Ford's 5% improvement statement.  But, It's conceivable that the covers could improve the laminar air flow significantly over the shutters which are "inside" the grill and thus lower the C_d to near to Prius range.  If the C_d could be brought down to 0.25 (a reduction of about 17% from the 0.30), the fuel economy impact should be about 10% at 70 mph.

 

I think we need more tests at higher and lower temperatures and at a few more speeds.  When I get my covers, I will run tests but unfortunately (or maybe fortunately) i won't be able to run low ambient temp tests. :)

 

Edit: what we don't know is if the 0.30 is with the shutters closed or open. 

Edited January 5, 2013 by Plus 3 Golfer

[ptjones]

This is what Ford says about the active shutters. 

 

 

So if the C-MAX has a C_d = 0.30, the shutters reduce the coefficient to 0.285.  This will equate to roughly a 3.3% improvement in FE at 70 mph all other things being equal (assume reasonable values for frontal area and rolling resistance).   So, from the graph the MPGs at 70 mph at 63*F are about 41 and 44 or a difference of 3 MPG.  That's about a 7.3% difference over 2X what I would expect from the shutters alone per Ford's 5% improvement statement.  But, It's conceivable that the covers could improve the laminar air flow significantly over the shutters which are "inside" the grill and thus lower the C_d to near to Prius range.  If the C_d could be brought down to 0.25 (a reduction of about 17% from the 0.30), the fuel economy impact should be about 10% at 70 mph.

 

I think we need more tests at higher and lower temperatures and at a few more speeds.  When I get my covers, I will run tests but unfortunately (or maybe fortunately) i won't be able to run low ambient temp tests. :)

 

Edit: what we don't know is if the 0.30 is with the shutters closed or open. 

I don't think the shutters are closed at 70mph for very long unless the ICE doesn't get up to temp. Which means there used for temp control primarily. Would be nice to be able monitor the sutters.

I have a small computer camera that I think I can tape on to grill and plug in to laptop. I need to find USB extension cord.

[MikeB]

Honestly, I think the aerodynamic gains from a grill cover should be really minimal. Given the shape of our vehicle, there's probably more to be gained by tapering the tail of the vehicle than there is by smoothing the nose slightly. Which implies that the biggest gain from the grill cover is thermal, keeping the engine warm. But the active shutters are there for exactly that purpose, aren't they? Which leads me to speculate that the active shutters aren't really doing their job. And if the active shutters aren't working properly, that might also explain why most people have so much trouble reaching the EPA numbers, assuming the EPA test was on a vehicle with functioning shutters.

 

ptjones, I'd really like to see the results of your camera experiment. And since I'm near by, I'll even volunteer to give you a hand with that experiment. The camera sounds like the simplest path. But as a more advanced experiment, I bet there's a message on the can-bus about opening and closing the shutters, if we had software that knew how to look for that.

[valkraider]

The EPA tests are done in warm temperatures and on a dyno in a lab where there is no actual wind (drag is simulated with the dyno).

 

Assuming the shutters are primarily for thermal management, at warm temps with no real wind a malfunctioning shutter would have much less impact than real world use in a 60mph 30degree airflow...

 

So yet another way real-world just simply doesn't match up with EPA test procedures.

[darrelld]

When our temps dropped into the 20's last week I noticed on ICE shutdown the engine temp would drop rapidly causing ICE restart. They need the water pump to have a variable speed motor to control engine temps better in colder conditions.

[MikeB]

The EPA tests are done in warm temperatures and on a dyno in a lab where there is no actual wind (drag is simulated with the dyno).

True, but apparently the dyno is programmed with resistance information based on a glide-down test of the car, which means both rolling resistance and aero resistance are factored into the test. Of course, then you have to look at how the shutters would function when the car is gliding to a stop, as opposed to actively using the engine. So you are right, this is another area where the EPA test needs improvement.

[valkraider]

Right, but on a dyno there is no wind blowing through the grill. So there is naturally less cooling effect going on regardless of shutters being open (or possibly Stuck).

 

The dyno only simulates drag - it doesn't account for the cubic feet of air flowing through the engine compartment from at purely thermal perspective.

 

This is all assuming that the thermal management of the engine is what is changing the fuel economy...

[ptjones]

 

 

Honestly, I think the aerodynamic gains from a grill cover should be really minimal. Given the shape of our vehicle, there's probably more to be gained by tapering the tail of the vehicle than there is by smoothing the nose slightly. Which implies that the biggest gain from the grill cover is thermal, keeping the engine warm. But the active shutters are there for exactly that purpose, aren't they? Which leads me to speculate that the active shutters aren't really doing their job. And if the active shutters aren't working properly, that might also explain why most people have so much trouble reaching the EPA numbers, assuming the EPA test was on a vehicle with functioning shutters.

 

ptjones, I'd really like to see the results of your camera experiment. And since I'm near by, I'll even volunteer to give you a hand with that experiment. The camera sounds like the simplest path. But as a more advanced experiment, I bet there's a message on the can-bus about opening and closing the shutters, if we had software that knew how to look for that.

Well I did it. I taped little video camera on center grill, I had to get a USB extension cord to connect it to the Laptop. Here are the results.

Shutters start opening at 190degreesF and gradually open in steps to fully open at 213deg.F. This confirms my idea that at 70mph most of MPG gain is aerodynamic not thermal because shutters are wide open. On my my trip to Phoenix and back my WT was 213-216degF 95% of the time. That is when shutters are fully open and there wouldn't be any aero advantage if the covers weren't there.My pics are in my gallery and it's hard to make out the shutters on the Laptop screen.

Edited January 5, 2013 by ptjones

[Chinto]

So your findings point to shutter control is triggered by water temperature. Staying fully closed up to 190 degrees and fully open at 215. So if this is functioning this way why does the WT remain less than optimum in cold, below 32 degree conditions? I would think WT would be more stable with thermal control shutters regardless of outside temps.

[robodog61]

I just foamed up my grill today and used the car's water temp gauge to monitor.  Temperature seemed to be more consistently in the middle and didn't drop too fast when the engine shut off like it did before.  Today was 40 degrees, so that may have had something to do with it.  I saw a small MPG gain and am up to 44 mpg on this tank of about 75 miles. I think there is a big hit on mpg due to low temps in this climate.  It was about 10 degrees a few days ago and the engine would cool down rapidly when the engine shut off.  I also notice that I don't hear movement of the coolant when you shut off the engine, like you do on the Prius.  The Prius has a "thermos bottle" that stores warm coolant when the engine shuts off.  It uses this warm coolant to more quickly heat up the engine when cold so you get up to the most efficient temps more quickly.  

 

I cover about 90-95% of the openings with the pipe insulation foam.  It was real cheap and easy to install, but looks kind of crappy.  I am really worried that if I block off all of the grill, there is a chance of engine overheating.  I mean, if all of the grill was covered and the fan kicked on, would there be enough cool air that the fan could suck on to prevent overheating?  I am starting to worry about causing damage.  All I have is the installed temp gauge.  Do you think it is OK to cover all or most of the openings?

[ptjones]

So your findings point to shutter control is triggered by water temperature. Staying fully closed up to 190 degrees and fully open at 215. So if this is functioning this way why does the WT remain less than optimum in cold, below 32 degree conditions? I would think WT would be more stable with thermal control shutters regardless of outside temps.

I estimate that my grill covers block 90% of the air to radiator, but there is still  air circulating around the ICE cooling it. The Shutters don't work as well as intended. With my covers I only had one time the temp reached 233deg. at 62deg. outside temp going uphill for a long time at 70mph. I have a ScanGuage to monitor WT,it thats the quess work out.

 

I'm going to sell a few more of the covers at $50 then I'm raising the price to $100 a set. There is to much time involved custom making each one of this covers. Not enough volume to pay for tooling to keep the price down.

[valkraider]

Don't read this if you don't want party poo poo. But I'm gonna be a little bit of a buzz-kill with this post...

 

Assuming these give a full 3mpg gain all the time:

 

Using $4 a gallon gas price, going from 37mpg to 40mpg or going from 40mpg to 43mpg will save a penny per mile. $50 break-even would then be 5000 miles. $100 break-even is 10,000 miles.

 

The gains get smaller with higher fuel economy. Going from 43 to 46 mpg saves less than a penny per mile at $4 gas.

 

Realistically lets assume that with temperature, weather, and driving variations that these can reliably net an average 2mpg gain. Lets put gas at the $3.50 point which is roughly current west coast costs. It will take more than 20,000 miles to recoup the $100.

 

I bet there is more petroleum product consumed in the production & shipping of the plastic for the covers plus the energy consumed to cut & shape them, then ship them to the driver will conserve by using the grill covers.

 

Throw in a potential fight with a dealer if there is ever an over-heating issue and all associated cost and hassle...

 

Sorry...

[plus 3 golfer]

Yes, I've thought about the potential risk of overheating and warranty. But as your math shows the return on investment is very good.

 

Manage the risk and reap the benefits.

[CNCGeek]

This is a great thread (hanks PTJones, Chinto and ByMaine for posting your data), and The mpg increase due to drag makes a lot of sense.  Looking into the grill opening, there does not seem to be a good place for the air to flow around the radiator with the slats closed.  It would be like driving around with an open shoebox mounted to the front of the car.  if a license plate frame can drop 1mpg, it would totally make sense that covering the grill could get you 4mpg.  I think I am going to scrounge around for some parts for a DIY cover.

[C-MaxJaxon]

Using $4 a gallon gas price, going from 37mpg to 40mpg or going from 40mpg to 43mpg will save a penny per mile. $50 break-even would then be 5000 miles. $100 break-even is 10,000 miles.

 

 

I was also thinking of ROI and taking into account that I wouldn't risk using them for 3-4 months per year when the weather is warm, maybe both of them only in the coldest weather and one in the spring and fall, so that increases the break even time quite a bit.

[plus 3 golfer]

Like most purchases, if you buy something and don't use it, it likely was not a smart economic decision to purchase it.  One pays a premium for a C-MAX hybrid.  If you don't drive it at least 100k miles, you'll likely never recover the additional cost of a hybrid (42 mpg) over a gas vehicle (30 mpg). At $4.00/ gallon that amounts to $3800 in fuel savings in 100k miles.  Same applies to the grill cover.  

 

In my case even living in the desert southwest, I'll likely get at least 10k miles per year use of covers at 70 - 80 mph as we travel back East usually in March / April and Oct / Nov each year. 

Edited January 6, 2013 by Plus 3 Golfer

[ptjones]

I was also thinking of ROI and taking into account that I wouldn't risk using them for 3-4 months per year when the weather is warm, maybe both of them only in the coldest weather and one in the spring and fall, so that increases the break even time quite a bit.

And here is the Positive spin on it.

 

If you look at my graph the average improvement is 4mpg and add in 1mpg for license plate holder for a total of 5mpg. So you will always have a center cover on, Summer time you would have one with cut out which should be good for 2mpg.

In reality the only reason for changing the covers at all is for the AC to work efficiently and if your speed is above 62mph all the time. If you are only using the ICE half the time it shouldn't get that hot.

With those numbers you could pay for the covers in one winter or 6-10 fillups.

 

BTW there is something plain wrong driving an CMAX  getting 31-35mpg during the winter and people ask what kind of MPG's are you getting. At least with the grill covers your getting 36-40mpg and people are still impress compared to what their getting.

 

BTW everyone that has seen the Grill Covers thought they looked good. Ford dealers,salesmen,service people and customers. Nice to do some to your car that improves MPG's and makes it look better.

 

You people are way over emphasizing over heating.  Having a ScanGauge changes the picture on over heating. The problem is just getting up to 200-220degrees to where the ICE works the most efficiently. Hopefully one of these days when it gets warmer We will be able to figure out what the range is on the CMAX temp gauge .  It would be good to know the temps for low and high marks.

 

I looked up on google the boiling point of 50/50 water coolant mixture at 21psi, 21psi is on the top of radiator cap,  is 285degF. So in theory as long as the coolant doesn't boil your OK. I would imagine there might be other problems prior to reaching 285degF.

ScanGauge is a good info tool, you can see issues before they become problems.

[valkraider]

License plate holders do not cost 1mpg.

[ptjones]

License plate holders do not cost 1mpg.

Did you test it? One of the other members though it did.

I thought you would be curious on how much range you would gain from grill covers on your Energi.

[valkraider]

On a 35 to 45 mpg vehicle, 1mpg is such a tiny change in fuel economy there is no way that a normal person in real world conditions could reliably determine if a license plate holder could cause that change.  It is all just hypothetical.

 

The license plate holder on the C-Max is largely flat and adds very little texture to the front of the vehicle - in fact the license plate is smooth and is applied over the decorative ridges on the front of the car, so just as easily the license plate holder could smooth air flow.

 

There is no way for normal people to know this without incredibly controlled tests.  Even figuring this out in a wind tunnel would be a complex process.

 

In the real world there could be differences in temperature, barometric pressure, wind direction, cargo weight, tire pressures, road moisture, humidity, or driver behavior which could cause the 1mpg difference which is being attributed to the license plate frame.

[C-MaxJaxon]

I question the accuracy of all MPG improvement claims posted online since it's very difficult for all the variables to remain constant or be adjusted for. Things like starting engine temperature, outside temperature, wind speed and direction, traffic, etc. all change between test runs with and without a mod in place. Then there's the possibility of the tester consciously or unconsciously behaving differently during the tests and getting the results they are hoping for. Doing a double blind test like scientists do would be necessary for a completely objective test.

[ptjones]

Having worked on airplanes I can tell you the license plate holder doesn't improve aerodynamics and mounting it on the cover does. I agree it would be hard to say how much.

I'm looking forward to you answering the rest of my post.