[DeTomaso] New Rear Window and Engine-Bay Cooling Fan

Sat Oct 1 23:11:48 EDT 2016

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:
http://www.snclocks.com/TheRestofourWorld/Autos/Technical-Bits/i-mN7wzjK .
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 way.

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 speed.

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 car/the radiator.

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.  

Stephen Nelson

-------------- next part --------------
   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:
   [1]http://www.snclocks.com/TheRestofourWorld/Autos/Technical-Bits/i-mN7
   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
   way.

   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
   speed.

   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
   car/the radiator.

   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.

   Stephen Nelson

References

   1. http://www.snclocks.com/TheRestofourWorld/Autos/Technical-Bits/i-mN7wzjK