Fun times. Now that all the 3.6 engines are getting to be thirty-somethings, we are seeing something we have yet to see on the 3.2 and earlier (930 based) cases, case through bolt breakage and/or leaking. Since this is a pressurized area the leak isn't a weep like a valve cover or oil return tube, it's a steady drip and gets worse with RPMs and oil pressure and temperature increase. Difficult to ignore.
We first saw this around 2005 when a customer decided to do an IG-RS conversion with VarioRAM on a 95 engine. That conversion adds solid rockers, better springs, a 7500 ROM rev limit and 993 EuroRS valves and bumps the horsepower to 325 or so. A nice upgrade if you are in for a top end. On that motor the upper through bolts above cylinder #1 and #4 broke about 3 years after the top end, and, these being pressurized they leaked like crazy.
We next saw this in the early summer of 2014 on a 964 engine that also had a recent top end. The engine was a 1990 low mileage engine with the head gasket issue but was otherwise in very good condition. The leakage began within a month of the top end, luckily before the engine was delivered to the customer. We warranted the repair.
A few months later we saw the leakage on another 1996 engine, the photos of that are below. Again this was an otherwise clean engine with perfect leak down and a legitimate 38,000 miles. We had been saving this engine for just the right customer and it back-fired. The first photo was taken through the fan-shroud cap opening and shows the leakage above cylinder #1. Remember that the upper case through bolts are pressurized and carry the oil to the main and rod bearings. Thirty hours later and $6000 the motor had a top end which it otherwise did not need.
Porsche and aftermarket suppliers have now issued their third revision of case through bolts. The originals, and all that come with bottom (case) gasket sets are blue silicone. The optional nitrile seals available since 2005 or so are green and are supposed to be better. The latest revision are a different durometer nitrile and are now red in color.
So if you are doing a top end or updating to late head gaskets on an early 964, add this to your list.
Now for the repair:
- Remove everything down to the cylinders. This cannot be done with cylinders in place.
- Protect rings from the studs and vice versa (nicks to either can be catastrophic)
- Remove and replace case through-bolts one at a time.