One of the most popular upgrades for the 911 is the addition or upgrade of the external oil cooler. Without a doubt, it is very important on an air-cooled engine to keep temperatures within an optimum operating range. The external oil cooler takes oil directly from the engine, and funnels it up the sides of the car to an oil cooler located in the front right fender of the car.
In 1969 on the 911S, a front mounted radiator-style cooler was mounted as standard equipment in the front right fender well. In 1973, the newer trombone, serpentine, loop or cooling pipe cooler as it was called, replaced the radiator style cooler. This style of oil cooler was used through 1983. The cooler was standard equipment on the 1973 911S, as well as the 1974-75 Carreras, but was optional on all other models up to 1977. In 1980, Porsche began using a 28-tube all-brass oil cooler in place of the trombone cooler (Figure 1) on all European 911SCs and Turbos. This cooler was claimed to have reduced the operating temperatures over the trombone cooler by 30 degrees F. The trombone cooler remained in place in the US, primarily because changing the operating temperature of the engine would affect emissions ratings.
The early trombone oil cooler wasn't designed to act as a traditional cooler. The oil cooler itself is just a few loops of piping that radiate heat. This trombone cooler is basically a turning point for the oil to come back to the engine. Some radiation of heat occurs in the trombone cooler, but a large part of the cooling process occurs in the lines running up the side of the car. A thermostat mounted near the engine controls the amount of oil redirected to the front oil cooler.
Realizing that this arrangement wasn't satisfactory for cooling the engine, Porsche developed the all brass cooler, which performed its job admirably. This brass cooler was used on all US and European 911 Carreras in 1984. In 1984, Porsche released an even better oil cooler. Returning to the finned, radiator style cooler, the Carrera oil cooler was mounted in the same spot as the previous ones, but had a large seal and stone guard to protect it from rocks and debris thrown up by the tire.
In 1987, Porsche added one more option to the fray. An electric fan attached to the front of the oil cooler, and controlled by a thermostat on the top of the cooler added an additional amount of cooling for the motor. The Carrera oil cooler with the fan attached is the desired upgrade for just about any 911 lacking one (all 911s made before 1987). This setup allows you to maintain the stock look of your car, and obtain better cooling with a minimum of modifications to the chassis.
The Carrera oil cooler, mounting kit, and flexible oil lines are shown in (Figure 2). Not shown in this picture is the horn bracket, the fender strut, or the large spongy seal that mates the cooler to the inside fender. When purchasing a used oil cooler, make sure that you obtain it from a reliable source that will guarantee its condition. As these coolers age and get beaten around, they sometimes have a tendency to leak. Make sure that any cooler you purchase has been completely inspected and pressure tested for leaks.
So what's required to implement this cooler setup? It all depends upon what you have on your car right now. Here is a list of all the parts and widgets that you need if your 911 does not have any external cooler installed right now:
- Carrera Finned Radiator Style Cooler (About $450 used, 930.207.053.00)
- Cooler to Fender Seal (about $70 new, 930.207.353.00)
- Rock Guard and air guide for Cooler (should come with cooler, but $45 used, 930.207.319.02)
- Rubber Mounts (3 required, 930.207.239.00)
- Supply and Return Oil Lines that run down the side of the car ($200 used)
- Thermostat in right rear fender well (about $100 used)
- Flexible adapter lines to connect the cooler to the oil lines
- Fan for Oil Cooler
- Seal between the rock guard and the cooler (930.207.361.00)
- Thermoswitch for Oil Cooler (stock 930.606.118.00)
- Relay and relay socket for oil cooler (911.615.109.01 and 901.612.333.00)
- Enough wiring to hook up oil cooler fan and relay
- New Horn Mounting bracket & Fender Support (911.635.107.00 and 911.504.080.00)
- Upper bracket for mounting oil cooler (930.207.927.00)
- Lower bracket for mounting oil cooler
The first step in the installation is to gather all of these required parts. Some of them can be sourced from reliable used parts suppliers. Make sure that any oil cooler that you purchase comes with a warranty and has been properly cleaned and pressure tested. These oil coolers cost a lot of money, and you would hate to get stuck with one that is leaking.
When you are ready to install the new cooler, the first step is to remove the old one. For now, we'll assume that your car is already equipped with a trombone-style oil cooler. We'll go into the details of adding the lines that run up the sides of the car later on. Jack up the car and remove the front right wheel. This will give you plenty of access to the oil cooler and the lines (Figure 3). Now, take two wrenches, and disconnect the long metal lines from the cooler. Be very careful when disconnecting the hard metal oil lines from the small flexible oil cooler lines. There are a set of thin Porsche tool wrenches that are designed to be used in this process. Although it is recommended to use these wrenches, you can also use two adjustable crescent wrenches.
When removing the lines, make sure that you hold both ends steady with another wrench. The lines themselves are not strong enough to support the twisting motion on the ends, and you can actually twist and damage the metal as you remove the lines. Work slowly and carefully, and don't forget to support the lines when trying to disconnect them. The lines themselves might be slightly rusted and corroded. In this case, it may be wise to soak the area in WD-40 the night before. Another trick is to heat the entire connection using a small propane torch. This loosens up the joint, and makes it easier to disconnect. Be careful not to accidentally burn your paint when you are using the torch.
A very important note to make here is that you should be aware that the lines will leak oil when they are disconnected (Figure 4). Make sure that the right side strut and brake assembly is out of the way when you disconnect the wheel, otherwise you will soak it in oil. If this happens, you will probably have to take it apart piece by piece to clean your brake rotor and pads.
Once you have the lines disconnected, then you should be able to easily remove the cooler from its bracket (Figure 5). Be careful when removing it, because it will most likely be full of oil. Now, set up the new Carrera oil cooler to be installed. Install the top bracket into the flange at the top of the wheel well. This bracket is angled, and has a small stud sticking out of it. Attach one of the rubber mounts to the bracket, and then bolt the bracket to the car. The rubber mount that mates to the oil cooler should be pointing towards the rear of the car.
Affix the two rubber mounts to the bottom of the cooler. Make sure that you place the small rock shield that covers the bottom in the correct orientation. It should be attached to the rubber mounts, fitting flush up against the right angle bracket. Install the right angle bracket to the bottom of the oil cooler, capturing the air guide.
Now, make sure that the rock guard is firmly attached to the oil cooler. A set of clips, similar to the headliner clips should keep the shield firmly planted onto the cooler. There is also a seal that goes around the two oil inlets, and between the cooler and the shield. Make sure that seal is in place prior to clipping the rock guard together with the cooler.
Now, press on the large spongy seal that goes around the edge of the cooler. This seal is quite flexible, and should be pressed onto the cooler until it snaps and locks onto the edge. Make sure that this seal follows the edge of the cooler around every curve and turn that the shield makes.
The thermostat should be installed and wired at this point. The original factory thermostat clicked on the fan at about 240 degrees F - way too hot for some people's tastes. There is an alternative thermostat switch that will start the fan running at a much cooler 210 degrees F. This switch is actually a compatible BMW part. Install this thermostat switch using a new aluminum sealing ring to make sure that it won't leak. Run the two wires from the switch to the fan, and couple them with the fan's own two wires. These wires need to be routed into the front trunk. I recommend threading them through one or more of the holes that exist for the wiring of the front headlamps and side marker lamps.
Another problem you will probably experience is a conflict with the horns. The large fan on the front of the car will most certainly impact with the horns. The solution on the later Carreras was to install a different fender strut and horn support bracket. The old one can be removed by loosening the three bolts, including the one that is located inside the headlamp bucket. You will need to remove the headlamp to do this.
The relocation of the horns is the trickiest part of this project. A new hole must be drilled in a very tight space for the fender strut to be mounted to the inside of the car. This hole, indicated by the white arrow in (Figure 6), can be drilled in the sheet metal support that is welded to the inside of the fender well. It is possible to reach behind this area to place a nut on a mounting bolt. Figure 7details the mounting points. The green arrow shows the nut that is welded to the fender strut. The bolt that threads into this nut is located at the bottom of the headlamp bucket. The yellow arrow points to the spacer used for the fender strut, since the newer style struts do not align exactly with the older style valance panels. Attach the fender strut to the fender, and then use the hole in the fender strut to align your hand drill to the proper spot to place the hole. On the outside of the fender, you will probably need a small spacer, as the new fender strut does not match up perfectly with the older valance. (Figure 8) and (Figure 9) show the horns relocated into their final position.
Once you have relocated the horns, it's time to install the oil cooler. Lift the cooler up into the fender well, and let it hang on the upper bracket. Fasten down the bracket with a nut to make sure that the cooler doesn't fall off, but leave it slightly loose at this time. The lower bracket eventually needs to be welded. We will assume here that the welding of the bracket is going to be done by someone else. The best bet in this case is to install the cooler, mark the location of the bracket, and then drive the car to the welder so that the bracket can be attached. The cooler does not need to be removed in order to weld the bracket in place - it can be pushed and manipulated out of the way. You can drive the car a short distance with the cooler hanging from the one top bracket. Just make sure that this bracket is installed very tightly when you leave your garage.
Once the cooler is mounted, you can now attach the oil lines (Figure 10). Loosely attach them to the hard oil lines that come from the engine. Then try to mate them with the openings on the oil cooler. This may require some tugging and bending of the oil lines, as they are a tight fit. If necessary, remove the oil cooler, and bring it closer to the metal oil lines. Have an assistant hold the cooler for you while you get the threads on the lines started. Once the nuts have been started on the threads, remount the oil cooler to the top bracket. Finally, tighten up the lines after the cooler has been placed back into position (Figure 11). Make sure that you use two wrenches in order to prevent the lines and the oil cooler connections from twisting.
The Carrera oil cooler is shown installed in the front fender well in Figure X. The lower bracket must be welded to the inner fender well in order to firmly mount the cooler. Note how the large seal that surrounds the cooler mates with the inside walls of the fender. The rock guard for the cooler is clipped onto the side of the cooler, and prevents rocks and debris from hitting the finned portions of the cooler.
With the oil cooler installed, and the lines attached, the only thing remaining is the welding of the lower bracket, and the wiring of the fan. Bob Tindel, Technical Advisor for Pelican Parts, offers us a good procedure for integrating the fan wiring into the car:
1. Grab your relay and relay socket. Examine the relay and socket to determine which relay pin sockets connect to which terminal on the relay. The wiring of the cooler fan should be routed through a relay that can easily be placed in one of the free spots in the 911 relay/fuse box. Shown in (Figure 12) is a standard black relay and socket that can be easily used to power the fan. The fuse box in (Figure 13) offers a handy placement for the relay, right next to the other ones that control the major systems of the car.
2. Wire terminal 30 of the relay socket to the bottom of fuse 13 (counting from the front of the car, in this case an SC. This fuse is a 25-amp, for the sunroof, rear wiper, and mirrors.) Use heavier gauge wire, such as 10 gauge.
3. Wire terminal 87 to the fan motor positive terminal, using 10 gauge wire.
4. Wire terminal 86 to the bottom of fuse 14, using 16 gauge wire (16 amp fuse, wiper/washer and cigarette lighter.
5. Wire terminal 85 to the thermoswitch, using 16 gauge wire (if you want to include a manual switch, also run a 16 gauge wire from terminal 85 to one terminal of a switch, and connect the other switch terminal to ground. A rear wiper switch works well for this, and can be located in the stock position. On many cars, the hole is already cut in the metal dash. You can locate it by pressing on the dash along the left of the steering wheel below the instruments. Cut out the vinyl with a razor knife, and the switch snaps into place.)
6. Wire the fan motor ground terminal to ground.
Before buttoning everything back up, confirm that the fan works properly and that it blows in the desired direction. It should activate when the ignition is on and the manual switch is closed, or the thermostat should turn it on at about 210 degrees F.
With the oil cooler installed, the only thing left to do now is to take the car to your welding shop to have the lower L-bracket welded to the side of the car. Needless to say, if you have your own welding equipment, you can install the cooler, take the measurement, and install the bracket yourself.
If your car doesn't have the oil cooler lines that run up to the front of the car, you will have to install them and the thermostat yourself. You will also need new lines that extend from the oil tank to thermostat and from the thermostat to the engine. The installation process is not very difficult. First, remove the rocker panel from the right side of the car. This should give you enough access to run the lines down the side of the car. It's a wise idea to take a look at another car with the lines already installed, just so that you have an idea as to where they should be mounted. The mounting tabs and brackets for the lines are held into the side of the car with sheet metal screws. Simply drill a small hole and then screw in the small rubber/metal brackets that hold the lines. The early cars used a different rear oil line setup than the later cars (1975 and up), so make sure that you get the proper lines for your car. Specifically, the rear mounted oil line will not fit onto cars with the later style heat exchangers.
There are quite a few more options other than the factory Carrera oil cooler for installation into your 911. Mocal carries an oil cooler that will fit within the fender well and costs a lot less than the stock factory oil cooler. (Figure 14) shows the lines and the thermostat, which is located in the rear right fender well, just in front of the wheel. The two lines that bend downwards go to the rocker panels, and run to the front mounted oil cooler. The two lines that exit out of the thermostat go to the engine and the oil tank.
Installation of the oil lines from the rear of the car is not too difficult a process if you have all the correct parts.
What about the air circulation in the fender well? On the late-model Carreras, Porsche notched the bumper to allow more airflow into the region where the fender-mounted oil cooler is located. This particular car is a 911SC, and the bumper removed and notched at a local machine shop. Notching the bumper and adding the oil cooler scoop are probably the two best methods for increasing the air flow to your oil cooler. (Figure 15) shows this notch cut into a 911SC bumper.
A brand new product, this oil cooler scoop replaces the side marker light on the right side of the car. Molded and formed out of fiberglass (Figure 16), the matte surface matches the rubber of the 1974-89 911s perfectly, and looks very much like a standard factory accessory. It is a bolt-on air scoop that replaces the 911 side marker lamp, and provides additional cooling to the inside of the fender well, as shown in (Figure 17). The scoop channels air from the front of the car into the fender well where the front mounted oil cooler is located. This area is sealed off most of the time, and actually receives very little fresh air. For the cars without the cutout bumper, this scoop provides the necessary air and cooling that is needed to take full advantage of the oil cooler. At the time of this printing, the scoop is available only from Pelican Parts (1-888-280-7799). It is a bolt-on air scoop that replaces the 911 side marker lamp, and provides additional cooling to the inside of the fender well.
For more information on this installation see the following resources:
- Our Pelican Article on the Oil Cooler Scoop Installation
- Up-Fixen der Porsche Series from the Porsche Club of America. Volume IX has a detailed article on this procedure starting on page 22.
- Porsche Cars North America has a Technical Bulletin, dated December 17, 1984 regarding the upgrade of the brass tube oil cooler to the new Carrera radiator style cooler. Part Identifier 1741, Number 8406