Porsche 964 C4 Oil Leak Repair Rennsport Kansas City

Had this little C4 in the shop this week to fix a couple of nagging oil leaks.

One of them was a leaking oil line from the reservoir tank to the thermostat. A real bugger to get out actually.

Then we had a nagging leak from the main oil line from the case to the reservoir. The old style line was rubber crimped, which ran right next to the hot exhaust. That doesn’t work over time. The downside is that the entire exhaust has to come off to replace this line.

Because it runs up over the top of the factory heat exchanges to the case. Not enough room. With aftermarket headers, it is possible without full removal.

So off comes the exhaust.

And a better shot at where the line attaches.

New, updated line in place with the upgraded braided hose to resist the heat of the muffler.

The downside of pulling heat exchangers on these old cars are broken studs. No matter how careful you are, if you do enough of these, you will break studs off due to corrosion. A steel stud in an aluminum head over time will create galvanic corrosion and they will become one.

But I have a way of dealing with broken exhaust studs on heads. I love this tool

After selecting the correct die for the exhaust port, the tool is installed over the broken stud, and a pilot hole is drilled using the proper bushing.

A hole clean through the stud. Next, you change to a larger bushing and drill bit and drill you next size.

Once that is out, you simply take a small pick and catch the only part of the stud that is left….the threads.

And with a pliers, carefully pull the stud threads out of the threads of the head.

The tool is so precise, it drills close enough to remove almost the entire stud WITHOUT damaging the original threads in the head. All that is left of the old stud are the threads. The procedure will work on pretty much all exhaust ports of different model heads. It is slow, very precision work, but it does a fantastic job of not messing up the head. Trying to center punch and drill out a stud while keeping everything perfectly straight is almost impossible. You might get lucky, but the odds are against you.

A thread chaser will clean the threads and will almost always just turn in and out by hand.

And at that point, the exhaust can go back on.

More from the Blog


Leave a comment
Frans Bunschoten

October 23, 2012 at 7:58 AM

Nice job on the stud drilling! Wouldn’t it be possible to simply weld a nut onto the broken off stud? the heat shock might also break the bond between it and the alloy head. It has worked for me on broken off studs in aluminium suspension parts, don’t know if it would work on a cilinder head.


    October 23, 2012 at 11:46 AM

    Often times on a stud large enough, you can weld a nut (especially if the shaft is exposed) and get it to turn out. On a small 6mm bolt though, your only access is to weld through the center of the nut, which is a pretty small opening to get a hot enough bead to not only weld the nut to the stud and keep it from just breaking off again when you apply torque, but also enough head to break the stud loose.

Udo Reisinger

October 31, 2012 at 12:38 PM

Fantastic 964 posts. I might have to share a couple to these projects with the guys over at Rennlist.com (964 forum). As a 964 owner, I really appreicate you showing us your work. I also like your style, you seem very relax during these projects. I always feel it’s a pain for my mech., would love to drop my car off at your shop if I didn’t live in North Carolina.

    Udo Reisinger

    October 31, 2012 at 12:39 PM

    appreciate…not appreicate…


    October 31, 2012 at 12:44 PM

    Hi Udo,

    My pleasure! I try to document work for owners so that they can see what is being replace and why rather than telling them “XYZ part” has gone bad and needs replacement, and them not really understanding what is happening. No matter how you explain it to them, people are visual learners, so the blog helps! My handle at Rennlist is PorscheDoc


Udo Reisinger

November 5, 2012 at 8:53 AM

Thanks for the reply Karl. I’ll keep a lookout for your post over at RL.

Steve Burleson

October 31, 2013 at 7:36 AM

I have a broken head stud on my 91 964. I am being told by every Porsche mechanic that to fix this, the motor needs to be removed and a top end rebuild must be done. The shops are estimated 12-15k for this! Other than the “popping noise” I am hearing when the motor is running, it is running fine!

Do you have any suggestions? Any help you can provide is greatly appreciated.


    October 31, 2013 at 7:41 PM

    Hi Steve,

    Unfortunately pulling the engine and breaking down the side with the broken stud is the bare minimum that should be done. While you could get away with doing just one side, it would probably be foolish to not tackle all the studs on both sides as they will eventually fatigue and break as well. There is no cheap solution unfortunately. While you can probably do a bandaid fix of just that one stud, it will still likely run you 6-7k parts/labor.

Leave a Reply