I've decided to take SVOboy's advice and make a grill block for my van. The only question is I'm really not sure where to start. I've taken some pics of the front to get some ideas. I'm planning on using foam and corrugated plastic as SVOboy suggested. Also I live in Southern Mississippi where it can get pretty hot. I"m not sure if I should cover the top and bottom middle portion. Both lower sides will definately getting covered because the openings serve no purpose without fog lights. I called a sign shop and they have
4' X 8' corrugated plastic for $15 and 18" X 24" for $1.50. How much do you guys think I will need?
i'd try to see where the radiator actually is. the grill may not represent the actual radiator surface, for example i only recently found my radiator is offset to the right. so try to figure out wich areas of the grill are most effective and block everything else off...
also you might want to try to make a cardboard or tape grillblock first. you can start with a small portion and add more surface untill things get to hot. so you don't waste any material and once you've determined what works best you can make an extra effort to make it look good.
If you want to give this a test before you make any significant investment, you can. On the van, their is a plastic cover over where the radiator and condensor are located. Their is a gap of about 3/4 of an inch between the two. You can remove the cover and put a sheet of cardboard in it, to block off the air's ability to pass through the radiator.
When I had one on my wife's van, I had to leave about 1/4-1/3 of the radiator unblocked, in order to keep the temperatures from climbing beyond their normal 25 percent point. I was pretty surprised at how much of an improvement it made. I took it off because it is primarily driven by her and I didn't want her to experience any problems because of my tinkering. I do think it was effective, on the order of 10-20 percent improvement in mileage, but you can give it a test run, before you go more permanent, if you want. You may very likely get a little better results with a more elegant approach, but this would give you a pretty good rough cut.
Gary I looked under the hood and there is a descent size gap between the radiator and grill fins. If I were to place cardboard behind the grill fins, then the block wouldn't be flush. Is being flush an issue or is blocking the grill the most important thing?
Well, ... ? I don't know, for sure. From what I've read, mostly here and my own experiments, it is probably slightly less effective than a gap cover or fill, as you are considering. When the gap's are blocked, the air inside of them doesn't have any place to go, so it creates a sort of mini bubble, which is probably not quite as finished in terms of airflow, as a nice smooth surface. However, from what I experienced, I suspect that it probably addresses better than 80 percent or maybe 90 percent of the opportunity, on a relative basis.
On my wife's Town & Country, 98, the first pass I used Saran Wrap across the whole front of the car. The second pass, I used the cardboard. I haven't done a more finished test, but I would expect it would be as good or better than the cardboard quicky test.
Remember that the goal is to improve the aero, not necessarily reduce cooling.
The engine can probly cool OK with a third of the grill open (depending on the car). If you use the AC in high heat and you have very little air coming through the condensor (sits in front of the radiator), the compressor will have to work a lot harder.
Reality is merely an illusion, albeit a very persistent one. - Albert Einstein
My take is, it's both aero and cooling.
Any air that skips over the hood or is pushed cleanly to the side is better than having it bang around in the engine compartment and under the car. That's the aero improvement. For that to work optimally, you want a nice smooth surface at the front of the grill so the air can slide off cleanly. But even blocking it behind the grill is better than letting it get in, as far as aero goes.
Cooling probably becomes more important in cold weather but it has to have an effect in warmer weather also. Cold air flowing through the engine bay cools the engine so the system has to sap off combustion heat to keep the engine up to temperature. The point is, any air going thru there that's in excess of what was needed to provide cooling at the radiator and for a/c is going to cause some unwanted engine cooling. (Remember the original Beetle was entirely air-cooled).
Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.