Porsche 996tt Weak Links:  Top 10 Issues for Unmodded or Modded Cars.

Here at Protomotive, we’ve been asked to help out with a list of weak links for those building and tuning the Porsche 996 Turbo.  We’ve seen a lot of them over the years!  And encountered even more due to the high levels of modifications we do on these cars.  Even though the 997.1 turbo is very similar, and some of these cross over, we’ll just cover the 996 turbo in this episode and work on a similar list for the 997.1 turbo owners.

Here’s the youtube video link if you’d prefer to watch! 

My Bungs Fell Out! (Top 10 common failures and weak links for Modded and Unmodded Porsches)

In the next post, we’ll go over the weak links due to power increases.  Today we’re covering some basic weak links that everyone should be looking at.  Some are due to age, others are due to poor engineering or oversight during manufacturing.  Mostly on the engine since that’s primarily what we work with here, but there are a few at the end on the trans and even a/c system.

Don’t get me wrong.  These are amazing cars!  And I love my 996 Turbo.  It’s absolutely my go to car when I want to drive, relax and have a little too much fun 🙂

So, here’s the Top 10 we came up with: 

1. Coolant Bungs

Yes, Porsche actually epoxied in the coolant bungs on these engines.   I’m not sure what they were thinking here other than they didn’t want the cars to last forever.  So let’s build in a few time bombs. The coolant bungs are randomly popping out now, spewing coolant all over your engine leaving you helpless on the side of the road 🙁  We highly recommend taking the time to remove all the castings.  Remove the bungs.  Lol, most of them just fall out when you grab them…  They’re that loose!  (See below) Clean the castings and weld in a set of our billet coolant bung replacements for a permanent fix.  Pinning them is only another temporary fix since the epoxy is already loose and leaking.  Yes, it keeps them from blowing out, but doesn’t stop the leak.  So, please weld them and be done with it!

Here’s the repair bungs to weld in: Click the picture to be taken to the page.

2. Plastic intake manifold problems

We’ve seen quite a few of these now with the plastic intake manifold plenum pinched where the lower hose clamps are placed on the block off for the lower resonance tube.  993s use this with a flap.  And that’d be awesome on these cars too, but there wasn’t space for it.  The plastic is getting deformed by the flat part of the clamp.  Then when it leaks and is tightened, it’s taking that flat and folding it inward to a pinch which now is a leak.  So, the more you tighten it, the deeper the pinch gets and the more it leaks.  This can be gently heated and reformed as long as it hasn’t cracked.  Cracked ones must be replaced since these are PA6GF30 material which doesn’t respond well to any glues, even epoxy.  Nothing sticks to Nylon (the PA6 part).  And the individual runners aren’t that costly.  And they’re relatively simple to replace, even with the engine in.

Here’s the part number → 996 110 215 71

3. Oil pressure senders

These are dinosaurs left over from the 70s, or maybe even earlier.  The 997.1tt got a nice update with a proper new sender.   The 996tt still uses the age-old pressure sender with a wiper resistor.  The wire crimps get loose, the nuts fall off and the senders just plain wear out since there’s a lot of moving parts inside.  So before condemning your engine due to flakey oil pressure, replace your oil pressure sender.

Here’s the part number → 996 606 203 02

Click the picture for a link

Here’s a Rennlist discussion about this and how to replace it! → https://rennlist.com/forums/996-forum/505634-oil-pressure-sender-unit-replacement-diy-6.html

4. Oil cooler

The oil cooler on these engines uses the engine coolant to maintain the oil temps.  Rather than old school air to water coolers, they moved on to a water to oil style radiator mounted on top of the engine.  If for some reason you have milk chocolate coming out of your drain plug, don’t automatically assume it’s a blown head gasket.  These coolers are very delicate and can split internally.  Causing you to chase around this crazy loss of coolant and intermix of water and oil.

Here’s the part number → 996 107 025 73

Click the picture for a link

5. Variable lift intake lifters

These are quite a marvel of technology.  Allowing a very small amount of valve lift at idle and light throttle to reduce drive by noise for TUV, improve fuel economy and reduce emissions.  However…. The original ones supplied in the 996tt’s have a problem that tends to get messy if they’re not dealt with.   The tiny pin that slide back and forth to allow the low or high lift tends to slide out a little too far!  This starts gouging the cam housing.  For some lucky owners it either stops, or merely machines a groove in the housing. The unlucky get a valve stuck wide open and the piston comes back and smashes it and it goes to hell in a handbasket from there.  Porsche superseded these lifters and resolved the issue, but didn’t do a recall as the problem wasn’t too widespread.  So, it’s up to the individual to take care of this and prevent a mess down the road.

Here’s the part number→ 996 105 255 25

Click the picture for a link

6. Piston rings on the ends of cams

Yes, I covered this in another video more in depth.  “Engineering Explained (Porsche cam tech)â€.  But quickly here, the rings degrade and cause the cams to lose control.  The 997.1tt got a huge upgrade here, but has its own share of camshaft issues with the slipping sleeve issue.  So, whenever you’re there, replace those rings.  Or if you’re having cam control issues, it’s most likely that the rings have gone away.  We see this most in extreme hot weather conditions cars, or poorly maintained with bad oils.  The ring can wear, or break into little pieces then disappear into the rest of the engine.  Many times, causing no other damage other than the cam losing control and flagging an error.

Here’s a link to the YouTube video I made all about this! → 

Engineering Explained (Porsche cam tech)

7. Intermediate shaft bolts

No, this isn’t at all the same as the dreaded Boxster, Cayman and Carrera intermediate shaft issue.  These are the Metzer engines and have a really nice design for this.  But someone at Porsche decided to leave off the locking washers that have been there from day one.  And go figure, the bolts back out.  So, if you’re getting funny cam deviation values, or a rattle at the lower back of the engine (back of the car that is), this could be the intermediate shaft gear coming loose and getting ready to cause chaos.  When the bolts back out far enough they get into the chains and well, that’s just not a good thing!  The GT3’s used a one piece intermediate shaft to resolve this issue, and a lot of high performance builds go this way.  But with proper locks, peens, wires, loctite or even welding, the oem shaft is perfectly fine.  We just need to keep the bolts in place.  Unfortunately, these are at the very heart of the engine, so not easily accessed.   But if you’re down there for any reason, please take care of this.

Gt3 intermediate Shaft left :: 996/997.1 Turbo Intermediate shaft with bolts to main gear right.

Here’s a Rennlist thread from people experiencing this issue → https://rennlist.com/forums/996-turbo-forum/980176-mezger-engine-noise.html

8. Oil gallery plugs

Here’s yet another thing that was never an issue, till they changed it.  The “new improved†oil gallery plugs are more like coolant channel plugs you’d see on a Chevy V8.  Designed to blow out in cold weather to save the block from cracking under extreme pressure from the ice.   However, oil doesn’t have that issue, so why are they there?  Cost?   The early 911’s had machined aluminum plugs press fit into the case.  The newer engines get these formed steel caps knocked in place.  Porsche released a TSB on the GT3’s having these pop out of the bottom of the case, dumping all the oil out of the engine and ruining the engines.  Luckily it’s not so prevalent on the 996 or 997.1tt but it does happen.  Following the TSB and peening the plug in place along with epoxying over them can save your engine from sudden disaster.  This is most prone to happen on extreme cold starts where the pressure is very high for a moment.  But can also happen as we’ve seen at high speed flying down the Autobahn!

9. Differential side plate

For most this will never be an issue.  But for track use or overly aggressive downshifters on the street the differential side plate is weak.  Even on a stock car, when downshifting very aggressively, this can break.  There are billet side covers available to remedy this.  A simple fix, easily accessible.

Here’s the part number if you’d like to see for yourself → 996 301 312 50

Patrick Motorsports has some you should check out 🙂 →  https://patrickmotorsports.com/collections/sidecover

  10. A/C and Heat flap

The foam has degraded over time and the flap will no longer close.  So in the winter your heat won’t work, but the a/c works fine.  There are great how-to’s online already.  I believe Rennlist has this writeup.

Here’s one of many Rennlist threads on this issue → Why does my car not blow warm air? No Heat. AC works. – Rennlist – Porsche Discussion Forums

And a link posted on this Rennlist thread explaining how to fix this issue → https://www4.rcf.bnl.gov/~nieuwhzs/986%20Heater%20Flap%20Repair.pdf

I’m sure there’s plenty more.  But these are the highlights.  If you think of any more, please tell us in the Comments!  We’d love to make this a great compilation of basic items for any new or long term owner of these amazing cars to be aware of.

Thanks so much for reading, be sure to watch our YouTube video on this topic and don’t forget to show the channel some love so we can keep making helpful videos for you!