Is your coolant leaking? It could be your coolant expansion tank

instructions FOR models:
  • 911 GT3 RS 4.0 - 997.2
  • 911 GT3 RS - 997.2
  • 911 GT3 RS - 997
  • More

Coolant is either your best water-cooled 911 friend or your worst leaking enemy on any 996 / 997 Porsche. With these cars aging one of the most common coolant leaks is actually quite easy/cheap to fix and involvea the replacement of the coolant expansion tank. The example below is from when we first started in 2005 and shows a 996 C2 going under the knife. But over 17 years later this same coolant expansion tank (and cracking issue) is found on any water-cooled 996 / 997 including the 996 TT, 997 TT, GT2, G3, GT3RS , GT2RS. What you can't see from the top with the decklid open is the bottom side of the coolant expansion tank which over time will harden and crack and leak out below on to the motor itself and floor (if it sits). Any time there's an engine out service for the GT1 based engine (Turbo, GT2, GT3) for a coolant-pipe fix we also change the coolant expansion tank. However, the expansion tank in those cars can also be replaced with the engine in the car.

Rewinding back to 2005

A customer called a few days ago saying his 996 Carrera had a coolant leak, asking if we could fix it. We focus on performance upgrades here, but he was hesitant to drive the distance to his dealer and since we are the closest shop, we decided to make an exception.

Coolant is a pretty nasty substance and this is a particularly messy job.

The car was a stock '01 Carrera with about 66,000 miles on the odometer. The car was not overheating or throwing lights, but would leave a small puddle of "something" after a long drive.

Once on the lift, it was clear there was something leaking right above the driver's side exhaust.

Looking inside the engine compartment, coolant appeared to be leaking from the lower half of the expansion tank. I removed the cap up top, and drained the coolant (using 5mm hex to remove the drain plug).

And while here, it's a good idea to change the thermostat, so I removed the four bolts holding the thermostat housing. To make these more accessible, it's necessary to remove the 3x10mm bolts holding the smaller hard line in place.

Here's the housing, removed from the car:

The thermostat's a bit tricky to remove from the housing without the proper tools, so I had James work his magic to remove it. :) I cleaned the surfaces of both sides, and replaced the gasket to reinstall in the housing and plug.

The culprit, seen from above, requires removal of the intake and air pump.

The tank attaches to a few hoses, the coolant level sensor, and a zip-tie. Once these are removed, it still has to slide out of its corner, which proved to be the most difficult part of the replacement.

I also had to disconnect two fuel lines, and lower the engine a couple inches in order to remove the tank.

The old tank, finally removed from the car:

I also replaced the coolant level sensor, because it was brittle and worn.

Here's the picture that tells the whole story... the new tank versus the old tank:

Just 8 years and ~60k miles ago, that yellow tank probably looked just the same! Next time you notice a small puddle behind a 996, 997, Boxster or Cayman, follow the leak up and you'll probably see something similar to this. But don't panic: it can be fixed.