While Porsche has gotten along with air-cooling for their sports cars for the past 50 years or so, it has come to my attention that all Porsche models are water-cooled, and have been since 1999. The reason for this new-fangled water-cooling is that it maintains a more uniform control over cylinder head temperatures. Air-cooling was much simpler and best of all, never suffered from coolant leaks. Or always did, but that was OK as well.

For better or worse water-cooling is here to stay, so we better get used to it. Modern cooling systems are sealed and once filled should never need additional coolant.

If a cooling system does lose its fill, it is imperative for us to find the source of the loss. If the coolant was there and now is not, there can only be a few reasons for its exodus. It might have leaked out of the cooling system and escaped to the ground. (A burst cooling hose or failed water pump is the most common failure).

A less popular escape route would be a leak into the engine itself. Coolant can find its way into the engine through a crack in a cylinder head or block, or by a failed gasket. If this is the case evidence will be found in the oil pan or exiting the tail pipe.

The method of determining the source of the loss is as follows:

Top off the cooling system. If coolant does fall out on the ground, trace it to its source and repair it.

If the coolant does not fall onto the ground in an obvious manner, you must pressurize the cooling system to simulate operating conditions. (See Figure #1)

Figure 1: Coolant pressure tester and adapters are Installed to replicate pressure under operating conditions

If the coolant does not escape quickly, you must leave the pressure on the system until the level drops notice- ably. If the coolant leaks into the cylinder, the engine will not turn over. You then remove the spark plugs, rotate the engine, and watch to see from which cylinder “Old Faithful” starts spraying.

If it leaks into the crankcase, the coolant will mix with the oil. After sitting for some time the oil and water will separate. Since oil is lighter than water, the water will settle on the bottom of the oil pan and pour out first when the drain plug is removed.

But what if none of these things happen? What if cool- ant is being added to the car slowly over time, and shows no signs of escape. This was the case for me a several years ago. While waiting for something to happen after pressurizing the system, I noticed a drip of coolant escaping the car.

But this was not a normal location for a coolant leak. The coolant was not leaking from the engine, but out of the right rear jack lifting point! Now this was a little perplexing as there are no cooling system components in the area. Then it hit me, (OK, maybe it actually dripped on me). The only thing that was even in the vicinity of the drip was the coolant reservoir mounted in the rear trunk. I looked in the trunk and started pulling carpet out to access the coolant reservoir. Under the carpet is wooden flooring, so out it went as well.

With all the coverings and floorings removed, there it was. A green fog of coolant spray was coming from the bottom of the coolant tank. A green lake had formed on the trunk floor. As the coolant collected on the floor it found its way forward through body panels until it escaped at the jack lifting point. (See Figure #2)

If you find that your Boxster is losing coolant in a mysterious fashion, you can simply pull back the carpet surrounding the coolant tank. Complete removal of the car- pet and flooring is only necessary when the tank is being replaced.

Coolant Tank Replacement

At first glance this seems to be a very straightforward process. The tank and mounting bolts are right there in the trunk. There is also an oil filler pipe integrated into the tank but that doesn’t look to be a problem. The problem lies not in the trunk, but on the other side of the firewall in the engine compartment.

That is where the coolant and oil hoses connect to the engine. They are connected with a series of pressure

Figure #2 Notice the lake of coolant on the trunk floor and the coolant deposits on the side of the tank.

clamps that you may have seen before on Japanese cars. You must remove these pressure clamps before removing the coolant tank. Getting to the clamps is another Issue. They cannot be accessed from the trunk or the top of the engine compartment. They must be accessed from the bottom of the car. Unless you are 10 Inches tall you will also have to remove the large aluminum protection plate on the bottom of the car. This is also not as easy as It seems. The plate is sandwiched between the chassis and some aluminum braces, which all must be removed.

If after all these obstacles, you still want to tackle this project, continue reading and I will attempt to guide you through the process. A factory service manual is highly recommended for this service procedure. This is due to the fact that there are several small details that may be omitted here due to space constraints.

  • Remove coolant and oil filler caps.
  • Remove reservoir cover and release coolant bleed valve (pull steel ring up into the locked position). Remove the top sealing ring of the reservoir.
  • Safely raise car and remove the plastic engine protection cover, and aluminum protection plate from the underside of car.
  • Drain the coolant at the bottom of the engine cool- ant housing. Reinstall the drain plug and tighten after coolant has drained.
  • Remove coolant pressure clamps and hoses from tank fittings. These are located on the engine side of the trunk wall, up high between the trunk and engine. (See Figure #3)
  • Now go top the top side of the car and remove all the trunk carpeting and wooden flooring.
  • Remove the electrical plug attached to the coolant level sender at the bottom of the tank.
  • Now remove the three mounting nuts and bolts holding the tank to the trunk wall.
  • The tank is sandwiched between Itself, a gasket and the firewall.

Figure #3: Fittings are way up Into this cavity between the engine and trunk firewall. (This is a good time to find a small-handed helper.)

  • Remove the oil dipstick and guide tube attached to the reservoir.
  • Carefully twist and juggle the tank while separating the gasket from the tank and it will come out. (The gasket should stay with the car)
  • Check the bottom of the tank to verify that the tank is actually cracked and the leak is not from the coolant sending unit. (See Figure #4)

Figure #4: Hold tank up side down and look for discoloration at leak points.

  • Once the tank is out use a wet/dry vacuum or other means to remove all the coolant from the trunk floor.
  • Transfer the coolant level sender and the three elbow hoses from the old tank to the new one.
  • Instead of reusing the pressure-style clamps replace them with screw type clamps. (This is a directive from Porsche when the pressure clamps leak, but is a good idea at replacement time as well.)
  • Mount the new tank (996.106.147.08 – price about $300.00) to the trunk firewall.
  • All earlier coolant tanks, 996.106.147.03/.04/.06/.07 have all been superseded to this 996.106.147 .08 tank. • From the bottom of the car, reattach the one oil hose and 3 coolant hoses to their original locations.
  • From the top of the car, reinstall the oil filler cap. Release the bleed valve, leaving the bail in the upright position. Turn the heater control to Max. Heat.
  • Fill the cooling system slowly with Porsche factory coolant part # 000.043.301.05. Mix this coolant with dis- tilled water at a 50% mixture. It is imperative to fill the system very slowly so as many air bubbles as possible can come to the top.
  • Fill the tank until the coolant meets the bottom of the filler neck. Now start the car let it idle, add coolant as necessary to maintain a level at the bottom of the filler neck. Install the reservoir cap. Raise engine speed to 2500 R.P.M.
  • Rev the engine quickly, several times during this process. The surging of coolant flow is needed to get all of the air pockets out of the system.
  • Let the engine temperature increase to 185 degrees and then close the bleed valve bail.
  • Continue revving the engine every few minutes until the coolant temperature reaches 195 degrees. After the engine temperature stabilizes, check below front radiators for hot airflow. (Cooling fan actuation)
  • Let engine come down to an idle and verify that the cooling fans are cycling on and off.
  • Check car for any coolant leaks.
  • If all seems well and no coolant leaks are present, reinstall the two lower covers.
  • After the car cools off completely the coolant level should be between the Min/Max indicator marks on the tank. If they are not, correct the coolant level.
  • As an extra precaution, you may want to re-pressurize the car cold, to make sure there have been no over- looked leaks.

    Good Luck