Boxster Project: Center Radiator

Radiators

The water-cooled modern Porsches have the radiator split into two sections, one in front of each front wheel. On certain models that require additional cooling, a third radiator is located in the center of the front bumper. In particular, a 986 Boxster equipped with the Tiptronic automatic transmission, a 986 Boxster S, and a 996 911, have center radiators. However, the 986 Boxster with manual transmission and 987 Boxster and Boxster S do not have a center radiator.

Stock Boxster bumper with vents for two radiators. (Click to enlarge.)

But the space for the center radiator is available behind the bumper, and the mounting points are there, too. Porsche sells a "GT3 Radiator Kit" that fits perfectly in the Boxster. I purchased mine used from a friend who was returning his Boxster to stock form in preparation for possibly selling the car. Once place that sells this kit is Performance Products. Make sure that you get everything needed: the center radiator, the two new hoses, the top and bottom mounting brackets, and the inlet air duct; I do not think that the kit from Performance Product (shown below) includes the inlet air duct, so make sure you purchase the correct one for your bumper separately.

Center radiator kit.

Bumpers

Of course, the standard Boxster bumper lacks the center opening needed to feed the radiator with air. Since most modern Porsche 986 and 996 front bumpers are interchangeable, you have a lot of choice. The Boxster S bumper has a center opening. Some 996 bumpers do. I selected a 996 bumper that has a center molding that is ready to be cut. A utility knife is all that is needed.

996 bumper installed with center bezel not yet cut out. (Click to enlarge.)

Cooling System

Boxster Cooling System

From what I've been able to piece together, the Boxster's cooling system flows in the following way. The dotted lines represent the addition of the center radiator. There are additional parts of the cooling system not shown here, such as the engine oil cooler (a heat exchanger), the heater core that uses the coolant heat to provide warm air to the cabin, and the transmission oil cooler (another heat exchanger that is present in Tiptronic-equipped cars).

Boxster Coolant Flow

What I haven't determined for sure is which direction those two dotted lines actually go. It may be the case that the hot water on the right side (rather than the left) is sent to the center radiator, and the cooled water merged back to the left side (rather than the right).

If you're unfamiliar with what a car's thermostat does, the idea is basically this. The thermostat is a simple valve that opens when it heats up. When the coolant is at a cold temperature, the thermostat valve is closed; this prevents coolant from flowing through the radiator, and thus causes the coolant to heat up because it's just cycling through the engine and the water pump, allowing the engine to warm up. Once the coolant reaches a temperature defined by the thermostat's rating (in essence, the desired engine operating temperature), the valve opens, allowing the coolant to flow through the radiator (which cools the coolant because of the air flowing over the fins, letting the heat dissipate into the air), thus keeping the engine at a steady temperature, or at least as cool as the radiators can accomplish. If the radiators do "too good" a job at cooling things down, the thermostat could conceivably close and allow the temperature to come back up. This is why it's important to have a thermostat that is the correct rating for the cooling system design.

If you're unfamiliar with the basic difference between coolant/anti-freeze and plain old water, it's simply this: coolant/anti-freeze has both a higher boiling point and a lower freezing point than water. This means it won't freeze at 0°C and it won't boil at 100°C. It will keep doing its job of flowing through the system and moving the engine heat around, at much lower and higher temperatures than water. The cooling system uses a mixture of water and coolant/anti-freeze. (Of course, because the system is pressurized, even a 100% water mix will not actually boil until something beyond 100°C.)

Temperatures

In my experience, the car has only run uncomfortably hot in certain conditions. First, the ambient temperature needs to be well over 90f°, usually over 95f°. Second, the car must be running an unusual percentage of its time at extremely high RPMs. Street and highway driving never meet this condition. And I do not simply mean driving on the race track. I mean driving on certain race tracks where the gearing of the car requires sustained use of the top of the rev band. In particular, I have found Willow Springs and the outside road course at Las Vegas Motor Speedway to force the car to spend extra time at high revs. At Willow Springs, I think this is because of turns 2 through 6, where a lot of time is spent at the very top of 3rd gear. At LVMS, I think it's because there are 2nd gear corners as well as a series of connected 3rd gear corners. It's also no coincidence that these tracks are very short (sub 1:40 lap times), and the car doesn't get much time at 4th gear at more moderate revs after doing all those extended high revs. Of course, this depends on the gearing of the particular model of the car. If you upshift at redline, the 2.5L Boxster transmission gearing puts you in 3rd gear from about 60 MPH to about 90 MPH; so tracks that have you spending a lot of time between 75 and 90 MPH mean lots of sustained high revs in a 2.5L Boxster.

When this happens, all it takes is half a lap of short-shifting (upshifting at, say 5000 RPM instead of at the 6700 RPM redline in the 2.5L) to cause the engine temperature gauge to fall noticeably. But that's not what you want to do when you are trying to do a good lap.

Bumper Removal

The first step is to remove the bumper. I would recommend reading Skyler's excellent instructions for this.

Skyler's bumper removal instructions »

However, it's quite simple, so I will outline the procedure briefly:

It is not necessary to remove the headlights.
Remove the wheels.
Remove the wheel well liners. There are several plastic rivets, several plastic nuts, and several screws. In fact, you don't have to fully remove the liners, but rather can detach the front half and fold the liner back to provide access to the front of the wheel well.
Remove the hood latch cover. Rotate the 4 plastic caps 90 degrees. Pull the cover off, carefully maneuvering the opening around the hood latch mechanism.
Remove the bumper itself. There are 2 screws on the top front, 3 screws on the bottom front, and two screws each at the side marker light (one accessed from below, one accessed from behind the light).

If you do remove the wheel well liners completely, it's a great opportunity to really clean and condition them with rubber/plastic conditioner. The before and after is pretty dramatic.

100K miles of road grime. (Click to enlarge.)

Cleaned and conditioned, like new again. (Click to enlarge.)

Radiator Access

Once the bumper is removed, you have to do a little more to get to the radiator plumbing:

Remove the metal bumper impact structure. Two large bolts.
Remove the radiator inlet ducts. Five torx screws each.
You'll probably need to unscrew the two plastic mounts that hold the AC line that runs across the front of the car between the two front AC radiators. Otherwise, there won't be enough slack in the AC line to move the radiators around.
Detach the radiators from their mounts. Several torx screws. Make sure that when they are hanging free, they don't put undue stress on the lines; hang them from the car using a wire if necessary.

This is another opportunity to do some cleaning and conditioning of the visible rubber/plastic material that turns grey over time. Clean those inlet ducts!

Before. (Click to enlarge.)

After. (Click to enlarge.)

You should definitely take this time to clean out the debris that accumulates between the AC condenser and engine cooling radiator on each side. If you look closely, on each side there are really two radiator elements. The front one is the AC condenser (basically, a different kind of radiator for the air conditioning system), and the rear one is the engine cooling radiator. There's about a 1/4" gap between them, and an astonishing amount of junk can manage to get in there, and this restricts the airflow and makes the car run hotter. You can push the AC condenser towards the center of the car until the little tab slides out from the slot. Leaves and feathers and cigarette butts and dust will suddenly fall on the ground. Gently brush and vaccuum off whatever junk remains on the radiator fins. (Skyler shows how to separate the two radiator cores in his instructions.)

This is the difficult part. Particularly on the right side, it's a cramped space to work in, which makes fitting and tightening hose clamps somewhat awkward. But it's doable. I would recommending getting a complete set of good, new screw-tighten hose clamps for all fittings. You probably can't re-use the spring-loaded ones already on the car, they're inferior anyway, and you need a additional clamps for the new hose connections.

Pinch off the hoses that you disconnect, in order to limit the amount of coolant that will spill out. Use a clean bucket to catch whatever drains out so that you can re-use it. It's bad for the environment and there's no point in not re-using it.

You don't need to attach the center radiator to the car until you've re-plumbed the left and right radiators. Just verify that you have all the mounting bolts and that it's correct before you dive into the plumbing.

Right Side Plumbing

The lower hose is replaced on the right side. The new hose has a Y in it to provide a new tube that runs behind the horns and over to the center radiator. Unfortunately, the rear hose section, which connects to the hard line on the car, is larger in diameter than the original hose. This means you have to really tighten it down to seal it.

Looking forward from inside the wheel well, you can see the new Y-shaped section of hose. The blue arrows show how the hose is oriented. It goes downward slightly to the radiator, and the new branch goes up and to the inside to the new radiator. (Click to enlarge.)

Looking directly back from the front of the car, you can see how the new branch is routed behind the AC lines and horns, along the front trunk wall, and to the new radiator. (Click to enlarge.)

Left Side Plumbing

The upper hose is replaced on the left side. The new hose has a Y in it to provide a new tube that runs back, down, and then forward over to the center radiator.

Looking forward from inside the wheel well, you can see the new hose, with the long, oddly shaped new section. The blue arrows show how the hose is oriented. It goes directly forward to the radiator, and the new branch goes back, down just forward of the metal line, then wraps under and around the lower hose, and finally forward to the center radiator. (Click to enlarge.)

Looking directly back from the front of the car, you can't see much except where the new long branch of hose leads out to the center radiator. (Click to enlarge.)

Center Plumbing

The center radiator mounts to the car's existing mounting brackets in the obvious places, with 3 bolts on top and 3 bolts on the bottom.

Bleed and Test

Now that you have everything hooked up, you have a bunch of air in the system; you need to re-fill the lost fluid, bleed out the air, and watch for leaks where you've connected things.

Mount the radiators back in their proper positions first.

Here are steps given in the service manual for bleeding the air from the coolant system:

Consider covering the trunk with plastic in case of a coolant overflow.
Remove the radiator cap, oil filler cap, and dipstick.
Pop the cover trim plate off the filler access area. This reveals the bleeder valve. If you remove the little screw above the trim plate to do this, be extremely careful to not drop the screw into any of the filler necks.
Flip the bleeder valve locking clip up to release it.
If you have an automatic transmission, remove fuse B1 (the ATF cooler valve).
Fill with coolant up to the bottom edge of the filler neck.
With the engine idling, occasionally revving the engine, fill up with coolant until there's no more room when the engine is revved. (Revving may raise the level a bit.)
Replace radiator cap.
Warm up engine until you are sure the thermostat is open. 10 minutes at 2500 RPM should do it, and you should hear the radiator fans come on.
Run 5 more minutes at 2500 RPM, revving to 5000 RPM every 30 seconds.
Carefully open the radiator cap, and top up the coolant.
Replace the radiator cap.
Run 5 more minutes at 2500 RPM, revving to 5000 RPM every 30 seconds.
Idle until the radiator fans cycle on and off once.
Carefully open the radiator cap, and top up the coolant.
Put everything back the way it was.

Check for leaks in your hose connections. Make sure everything is finished before you start putting the bumper back in place.

If you have the 996 bumper with the black plastic center bezel, you'll need to cut a hole in it. I'm not sure how universal this procedure is to other types of bumpers, but this is how it worked for mine.

If you look at the front of the bumper, there's an indented line that you might think is the place to cut. It is not. Look at the back of the bumper and the line traces a slightly different path. This is the place to cut. It fits the center radiator's air duct better, and more importantly it's all on an area where the plastic is fairly thin and is an easy-to-cut material. If you use the line marked on the front, some of the plastic is way too thick.

Use the contour marked with the green arrows here. Don't use the contour marked with the red arrow, which is the contour visible from the front. (Click to enlarge.)

Do a test fitting of the center radiator air duct against the bumper. This will help you see where the cut should be and where you wouldn't want to remove material. The black plastic insert on the bumper is contoured on the back to make a perfect fit to the rim of all three radiator inlet ducts. To be honest, I was pleasantly very surprised that it fit this way. I was expecting a much less exact fit. But in fact, these pieces were designed to fit exactly right.

Using a utility knife, make a careful, smooth cut along the line. You want to keep the cut as clean and straight as possible so that it won't be visible. My cut was not perfect, but any little flaws are all but invisible from the front.

Center hole cut from bumper, viewed from the back. (Click to enlarge.)

Center hole cut from bumper, viewed from the front. (Click to enlarge.)

Once you've tested the new plumbing and the new bumper-to-duct fit, you can put the bumper back. It's just the reverse of the removal procedure.

Of course, the first few times you drive the car, keep a close eye on the temperature in case something isn't right. If possible, after a week or so, re-tighten the hose clamps on the oversized hose connections that I mentioned earlier; this will require removing the front part of the wheel well liner. Check for any signs of leaks around the connections. On the other hand, if there are no symptoms of high temperatures or fluid loss, then everything is probably OK and you might elect not to worry about that.