[DeTomaso] New Rear Window and Engine-Bay Cooling Fan
Asa Jay Laughton
asajay at asajay.com
Sun Oct 2 01:19:33 EDT 2016
I would like to see more photos, outdoors sitting alongside other
But with that said and only seeing the two photos you have in your
gallery, my opinion has changed. I had my doubts that it would look
significantly different, but I must say that I think adding the rear
window easily adds a few thousand dollars to the car's appeal.
Honestly, I think it gives it a really nice clean look. It -does- look
like it's meant to be there.
You did a great job of engineering to make it work. I'm anxious to
read the article.
Asa Jay Laughton - W7TSC, MSgt, USAFR, Retired
& Shelley Marie
On 10/1/2016 8:11 PM, Stephen wrote:
For some time I have been thinking about installing a window in the
opening behind 5332's engine compartment. Originally there was meant
to be glass in the opening, but, according to Tom Tjaarda, there were
overheating issues and the window glass was left out.
I decided to firstly see what would happen with the opening blocked off
and the car idling. One 70 degree F day I blocked the opening and let
the car idle while I monitored the inlet air temperature via the remote
for my MSD fuel injection. With a hot engine and a 70 degree ambient
air temperature I saw the inlet air temperature go up at a rate of
roughly a degree Fahrenheit every 2 seconds. I quit the experiment
when the inlet air temperature hit 150F. As an aside, I had previously
noted when I was stuck in traffic on a hot day that the FI would get
finicky if I sat long enough. I figured the issue was excess
temperatures even with the opening behind the engine open.
Clearly it will get right hot in the engine compartment if one blocks
off the opening.
Earlier this year I did a series of tests to see how significant the
air flow was through the opening at speed. My testing showed the air
flow through the opening was around 20 to 25 feet per second (14 to 17
mph) at a road-speeds of 60 to 80 mph. The flow through the opening
equates to an air volume of around 2000 cfm at 70 mph. If I installed
glass in the opening I figured I needed to install a fan to provide a
reasonable flow to keep the engine compartment from overheating -
somewhere around the air flow rate when the car is going 30 mph -
around 800 CFM.
So, given I intended to install a window in the opening to keep from
pulling water and dirt and rocks and grass and whatever is on the road
up onto the engine when driving at speed, as well as to keep folks from
being able to reach in and take whatever they wanted off the top of the
engine, I figured the first step was to figure out how to keep the
engine compartment cool.
Looking at SPAL radiator fans - wow - even a 10" low profile fan puts
out 800 cfm. I thought this would be sufficient.
Next I looked below the car to see where I could hide a fan. Turns out
there is a great space below the coolant surge and swirl tanks - just
behind the bulkhead and above the frame rails. Measurements suggested
that a 10" fan would fit.
Next - how to keep dirt and rocks and leaves and the like from getting
thrown up into the fan. I did an online search for 12 inch circular
screens and found a rather novel solution - 12" stainless steel flour
sieves. Talk about a slick fit - check out this picture:
wzjK . You can see two of the angle brackets I used to mount the
fan/shroud to the frame rail and inner sill. There is one additional
bracket that mounts to the frame rail. When mounted, as shown in the
next 3 pictures in the above gallery, it is very solid and out of the
I set up a SPAL PWM (pulse width modulated) fan controller with a
Derale 16760 Push-in Radiator Probe to control the fan speed. I like
the PWM controllers - they ramp up fan speed as the temperature goes
above the temperature you choose as your lower target. Then, if the
temperature continues to go up, the fan is at its maximum speed when
the temperature hits your upper target. If you have a second fan, it
will turn on when the temperature hits your upper target. I use one of
these on the radiator fans for 5332 and on the fans for our '69 XKE.
I mounted the temperature sensor to the fuel line going to the FI
throttle body and set the controller to start spinning the fan at 140F,
with an upper limit of 150F, whereupon the fan is spinning at full
With the opening blocked, the fan, at full speed, brings the inlet air
temperature to the FI system down at about 2 degrees per second.
Worked like a charm!
After installing the new rear window Kels and I joined the PNW Pantera
Group for a run up into British Columbia - going to a car show in
Nelson. Logged around 1200 miles on that trip: The fan only came on
once - when we restarted the car after letting it sit for 30 minutes
while we were in a store. Fan came on, temperature dropped and it shut
off within 30 seconds.
When driving at speeds over 10 mph with the rear window in place the
inlet air temperature held around 40 degrees F above ambient. This
jives with what James Fusco told me - he explained that "the air that
comes into the engine compartment has already gone through the radiator
and along the bottom of the car". OK - that makes sense. And, it is
apparent that, even at fairly low speeds, there is a lot of turbulence
in the engine compartment, which keeps the compartments temperatures as
cool as could be expected, given that the air is coming from below the
Fortunately I mounted the engine-compartment cooling fan to one side of
the engine compartment - turning it on at speed does cool the inlet air
temperature. And, when sitting still, the fan is very effective since
it is likely drawing air that has not been through the radiator.
The fan blows air up the passenger side of the engine, across the top
of the engine compartment, and down the other side.
I've included a couple of pictures of the installed window in the above
referenced photo gallery, along with some pictures that I will discuss
when I put together an article for the newsletter. There are
definitely some challenges to getting the rubber around the window laid
in nicely - I will cover those in the article.
I think the rear window finishes the look of the car - it is surprising
to me how much more complete it makes the back of the car look. And,
before anyone howls about modifying the car - well, hmmm - it was
originally intended to be there - except there was no provision for
letting the engine compartment vent hot air when sitting still.
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