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Front Oil Cooler Venting for '74-'89 911s
By Steve Grosekemper
A popular update for '74-'84 911s is adding a front fender, radiator style oil cooler, as installed in '85-'89 factory 911s. While this cooler does a very good job lowering engine oil temperatures, it
has one design flaw. The problem is not in the cooler, but in the installation. Placed in the right front fender behind the headlight, turn signal and fog light, it doesn't get much direct airflow at
speed.
The way the cooler
does get its air is quite interesting. As the right front
wheel spins in a forward motion, air is drawn down over the
back of the cooler's louvers and creates a low-pressure area
that draws air through the cooler. The front of the cooler
draws air in from the only place it can, below the front spoiler
and from the tiny gap between the bottom of the bumper and
top of the front valance
The biggest improvement you can make is to increase airflow through the cooler. There are three stages of improvement, each one increasing in complexity and effect.
Stage 1
The easiest is to
remove the right fog light in '84-'89 911s ('74-'83s have
no fog light hole in the valance). Remove the 17mm lock nut
on the bottom of the fog light. Now you have a fog light in
your hand and a large wiring harness connecting it to the
car. It is not easy to disconnect the harness, so cut it between
the fog light and the car. Yes, that's right, I said cut the
harness. Then install a polarized 2-pin marine plug. This
allows the fog light to be removed and installed in less than
a minute! The marine plug is to keep dirt and moisture out
of the connection. When you are done, this setup will look
factory installed.
Stage 2
This modification is superior to Stage 1 because it introduces cooler air to the center of the oil cooler, instead of warmer air to the bottom of the oil cooler. Whether on a racetrack or on a hot
desert road, the same is true: the higher the air, the cooler the temperature. This is because asphalt temperatures can be as high as 150 degrees on a hot summer day. The air absorbs that heat, and
transfers it to your car.
This modification is made by removing the right front turn signal assembly in front of the oil cooler, thus creating a high pressure column of air forced directly into the cooler, which removes more
heat from the engine oil.
The procedure is as follows:
1. Recruit someone with very small hands (no joke).
2. Remove the turn signal lens screws and lens ('84-'89 911s*).
3. Reach up between the oil cooler and the front bumper, and locate the light housing mounting bolts.
4. Remove the two 5mm mounting
nuts and washers using a 1/4" drive ratchet and 8mm socket (your small handed assistant may now be dismissed).
5. Pull the housing from the bumper and let it
hang from its two wiring harnesses. One harness goes directly into the light assembly. Cut it about 2 inches from the bumper assembly. The other splits into two wires--brown and black with a white
stripe. Mark the housing with a permanent marker (brown and black/white) so the connections will not get reversed. Unplug the wires from the back of the light assembly and set it aside.
6. Take the housing, remove the Philips screw holding the chrome reflector. Remove the reflector and its wiring.
7. Take the bare
housing and turn it upside down. On the back you will find two 5mm studs on two vertical corners. In the opposite two corners you will find two circles cast into the housing. Drill a 1/4" hole
in the center of each circle. Take the reflector and grind or file out a 1/2"round piece from the top right and bottom left (bulb socket facing you). Reassemble the reflector and housing. You
will notice that the ground out corners are for access to the holes where our new mounting screws will go.
8. You will notice four mounting holes on the bumper where
the housing came out. Install a threaded insert into the top right and bottom left holes to quickly mount the light assembly from the front. There are several ways to accomplish this. One is to
install a Nut-sert, an aluminum or steel insert threaded on the inside and smooth on the outside. Installation requires a special tool that squishes the insert and makes the center expand and conform
to the hole in the bumper. You can ream the hole in the bumper so it is slightly smaller. Take a long 6mm bolt, thread it into the insert and press fit the insert into the bumper with a small hammer.
The last and ultra shade tree mechanic method is to take a 6mm nut and grind or file down the outside diameter to be just slightly larger than the hole. Then press fit in the nut.
9. Install a 3-pin marine plug on the three harnesses you cut. Install the male end of the plug on the light housing end to avoid short circuit problems with the light
removed.
10. Take your housing and plug in your new 3-pin connector.
Return the brown and black wire with white stripe to their
original locations (which you marked). Place the housing back
into the bumper, install two 6.0x1.0x15 mm cheese head screws
into the housing and the new inserts and tighten down.
Replace the turn signal lens and tighten the mounting screws.
* '84-'89 911s have an additional safety device (not on earlier cars)--an aluminum brace behind the bumper which may need to be removed in order to access the turn signal mounting nuts. It is held in
place by four long 8mm bolts. After the bolts are removed, the oil cooler may have to be partially removed to slide the brace out of the way.
You now have a quickly removable light assembly which will greatly increase airflow to the front cooler.
Stage 3
This modification is for the most die-hard racer who runs the car in long track events. We have covered venting the fog light and the turn signal. Now the headlight bucket! This air is the highest
(and coolest). The headlight bucket is a large opening, allowing the most air to be forced through the cooler.
Instructions are as follows:
1. Remove the headlight, unplug the bulb and set aside.
2. Draw a 5" x 6" rectangle in the bottom of the headlight bucket. Draw a line down the center. You may want to remove the cooler
from its mounts and let it dangle out of way of the saw blade. Yes, I said saw blade!
3. Now hold your breath and cut down the center line with a saw. Cut a 5" horizontal line on the
top and bottom of the rectangle. Fold the sheet metal down toward the oil cooler (we fold the metal down out of the way instead of removing it so it can be re-welded into place later, if you'd like).
4. There are two options. Either fabricate ducting between the bottom of the headlight bucket and the top 2/3s of the oil cooler, or fabricate a block-off plate from the bottom of the cooler to
the bottom of the spoiler. The air pressure is so high, it will escape from the bottom of the car and not get a chance to go through the cooler.
5. After the duct work is complete, a scoop must be added
to the top of the headlight bucket. The bucket is tilted so
far back much of the air falls out the top. Light fabrication
is necessary for this modification. You need a chrome headlight
rim from an early 70s' 911. Remove the plastic insert from
the inside and install a chicken wire grille to keep out rocks
and low flying birds.
Now install the headlight for street driving and the scoop for track events! A chicken wire grill should be installed in front of the fog light and turn signal openings just as was done in the
headlight scoop. One rock through the oil cooler, and your right front tire gets a 12-quart oil bath in a matter of seconds!
Here is a list of parts needed for each update:
Stage 1
1- 2-pin connector (Pollak Pt# 11-200)
1- one square foot piece of chicken wire
Stage 2
1- 3-pin connector (Pollak Pt#11-300)
2- 6X16mm cheese head screws
2- 6mm nut inserts
1- 1 square foot piece of chicken wire
Stage 3
1- 901.631.102.02 headlight rim
1- one square foot piece of chicken wire
1- lots of sheet metal and fabrication skill
Good Luck!
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