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MAX Update No. 80: Cooling Tests and Travels

Back in October of ’09 (MAX Update No. 35: Nose Job for Better Aerodynamics) I mentioned I believed MAX could get away with a much smaller air inlet for the radiator—about 1/3 the size of its original area (which was one square foot). And I calculated that this smaller inlet would reduce drag by about a horsepower in cruise, which is a significant bite of MAX’s modest horsepower needs. And then about a year ago (MAX Update No. 52: Cooling System Bug Report) I did some test driving with the air inlet partially blocked off, which gave me confidence in my calculations…enough confidence to make the cooling air inlet in MAX’s streamlined body about half the size of the inlet in the Escape from Berkeley body.

And my static experiments with low power fuel consumption (MAX Update No. 68: Idle Speculation and MAX Update No. 70: MAX's Theoretical Max) made me daring enough to start last month’s trip to Ohio with a small roll of white duct tape in my tool box, so I could experiment with closing off the inlet even further.


So here’s how MAX looked when I left Cave Junction (ignore the cardboard box in the passenger’s seat, it was a shipment I had to drop off at UPS on the way) with the radiator opening taped up to 60 square inches of inlet area—about 40% of its EfB size. Purists may think me snooty because I didn’t use the traditional silver-grey duct tape, but with the pink bandana on my face and the red plaid Elmer Fudd hat on my head, I think I looked sufficiently proletariat that the white duct tape passed without notice. It’s not like I was putting on airs.

The advantage of duct tape was I could hop out and tear it off if I had an overheating problem—remember, I’m still experimenting and still learning, and at this stage I preferred expedient to classy.

Up through Oregon (including a bumper-to-bumper traffic jam in Portland) through Washington, across Idaho, climbing into Montana and across the Great Divide and into Wyoming…no overheating problems, so I added more duct tape and narrowed the 5-1/2” tall radiator inlet to 8” wide. That’s 44 square inches, less than a third of the Escape from Berkeley nose opening. And that’s how I drove across South Dakota and into Minnesota, and by the way, did I mention there was a record heat wave going through the Midwest in mid-July?


This is MAX, a little south of Minneapolis, and this is Bill who is making a MAX of his own. Minnesota isn’t exactly on the short cut between Cave Junction, OR, and Lexington, OH, but I wanted to visit Bill and see how he was doing (quite well, by the way) plus take advantage of the heat to test MAX’s cooling system. If you’re wondering why the photo is fuzzy, it’s because even though the temperature was in the hundreds, the dew point was 81 degrees and fogged the camera lens. It was miserably hot and humid, but MAX’s temperature gauge never got out of the high hundreds so I narrowed the air inlet even more.


And here’s MAX in Indiana, with it cooling air inlet taped down to 5” wide and 5-1/2” tall. That’s 28 square inches; smaller than a paperback book, smaller than 1/5 the size it was during Escape from Berkeley. It cooled fine, though it was right up at the high edge of fine (I saw 220 on the temp gauge a couple times, when I was stuck in traffic) so I left it at that. That’s the size the opening has been ever since, and the minimal cooling drag is one reason MAX gets better than 100 mpg.

What have we learned from this? That by judicious reduction of airflow through the radiator, we can practically eliminate cooling drag’s contribution to MAX’s fuel consumption. There’s not much mileage to be gained by making the air inlet any smaller than it is now, but I can sure make it prettier, and adding an electric fan for traffic jams would make MAX a better city car.

Photos by Jacky Leggitt and Jack McCornack 

Browse previous MAX Updates.

Check out the 100-mpg Car page for all things MAX.

bill goodrich
9/3/2011 9:55:31 AM

Say Jack, I understand the fan because of effiency and safety, but what about using a choke pull to set up a sliding panel over the opening to reduce or enlarge as need manually? Remember the old cars had those to add vents to the inside of the vehicle.

9/3/2011 12:28:07 AM

Instead of a canopy, consider a tonneau cover over the passenger compartment. You could even tailor it in a similar fashion to a kayak cover and cover most of the driver's area. I have driven in Oregon for years and unless it's a downpour, this will keep you drier than you can imagine. I was a sport-scar mechanic for 20 years and founder of a club for Datsun Roadsters. I have lived in Oregon all my life. A tonneau is sufficient for most oregon rain. It's also cheap and easy to make and can attach with snaps.

9/2/2011 6:00:46 PM

A reincarnation of the Jag type E from the early 60's. One of the most beautiful cars ever. Lookin good!

abbey bend
9/2/2011 3:49:54 PM

Taking the turbulence out of the equation by covering the passenger compartment will more than make up for front area changes. Turbulence is a bigger factor than frontal area, all things being equal. As for the frontal intake area, if you want to really reduce the amount of drag caused by air going into the grill and forced under the vehicle, while improving cooling there is a simple, proven and effective method. Place a shield behind the grill, metal or wood, a few inches in front of the radiator. Have approximately a one inch gap around the shield's edge. Place a fine mesh screen, like window screen, in front of the grill or just behind it, but in front of the shield. This will improve the cooling on any vehicle because the air moves through the radiator slower, reduces the amount of air moving through the radiator and being forced under the vehicle. The screen causes a bow wave to form in front of the grill, creating a smoother flow of air over the top of the vehicle, reducing power consumption. Also if you make an air damn under the chin of the body, you will reduce the drag by reducing air flow under the vehicle, forcing the airstream over the top of the vehicle. Even with a full belly pan, over the vehicle is better than under the vehicle in relation to turbulence. All of these tricks are easy, cost effective and well proven in competition and speed trials. They also work at any speed over 25 MPH.

9/2/2011 10:24:47 AM

As I said before, being a diesel, the likely heat load required to overwork that radiator is so large (compared to the work it is doing) that blocking the grill off completely and only letting in the air pulled from beneath the nose flow through, is sufficient. I ran my F250 Diesel for a few years with the grill blocked of completely and even in the hottest 100 degree summer days, in stop and go traffic, my truck never threatened to overheat. What's with all this sneaking up on blocking it off? Just close it off and see!

jack mccornack
8/28/2011 8:44:48 PM

Jason, I do intend to give MAX a windshield/canopy--there's enough spare change left in the budget for an enclosed cockpit and it'll make MAX a year 'round Oregon car. But I'm not expecting an aerodynamic benefit. I believe enclosing the cockpit will reduce the drag coefficient, but will increase the frontal area more than it reduces the Cd so I predict it will hurt mileage a bit. But then again, I'm a bit of an Eeyore, and we really won't know until it's done and driven. However, even if an enclosure (my plan at the moment is a removable hardtop) hurts mileage a trifle, if it makes MAX practical for rainy days (of which we have many) then I'll drive MAX more and other cars less, which will save considerable fuel.

8/24/2011 8:00:44 PM

So what would happen if you made that a rear mounted radiator, and used an electric fan full-time to pull air from under or behind the vehicle rather than the traditional open nose system?

8/19/2011 9:22:44 PM

At last! more full body pictures! Do you think Max would benefit aerodynamically from a windshield/canopy? Do you have any plans in that area? If not, may I suggest a double bubble like the Batmobile? To the Bat-Cave Junction Robin!