Q – I own a 91 Carrera 4 and I love the car, the color, the interior, the sound…the whole package.   I would love it a lot more if I could drive it in the summer but I can’t because it leaks oil and the AC has never worked well for me.

I heard that the AC systems in these cars are really inadequate and that R-12 coolant is very hard to find. I have never really had it checked out.   Last year was really a scorcher and we drove it only 300 miles.   Two years ago, I had a major service: spark plugs, valve adjustment and had some oil leaks fixed but last year, the oil leaks were back.   I took it back to my guy and he tells me that the engine needs to be removed to replace the camshaft seal, something he did not work on before. So I am thinking that since I don’t drive it, I might want to sell it.   A family member expressed interest and I would want to get it fixed up before I sell it.   I am looking for a second opinion. What do you recommend?  Pete

A – First of all, I feel your pain!   When the AC doesn’t work, it is hard to get your honey to ride in the car! Oil leaks are another very annoying bad habit that some old Porsches have. I hate that stuff however, it’s job security.   We will start peeling the layers of this onion and as with an onion, there may be tears.   Hopefully you will not be crying a river.

Starting with the oil leaks first, the only external “cam seal” on your motor is called the power steering pump drive output shaft seal. They rarely leak but since the area is all wet, it is a possibility. The power steering pump sits right above that area so it must be considered a potential source as well.   Since the motor can shift around on its mounts, the lines that attach to the pump can loosen up or shrink.   This IS a common source of leaks in that area.   But diagnosis is where you begin.

I would remove all the external shrouds that conceal the valve covers, etc. Then, wash the engine with a cleaning solvent such as “Gunk Engine Brite”. This is almost always necessary, because oil leaks on 911’s usually go on for quite some time before they ever make their way to the ground; as they ooze slowly, the oil mixes with dirt and creates a wide-spread film of dirty, oily paste. This residue obscures the original source of the leak, a sort of “trees for the forest” camouflage.

After scrubbing and brushing the oily residue off the engine, add leak detection dye. After warming the engine up, the suspect areas can be viewed with ultraviolet light and the easy leaks can be spotted.   Then the car needs a good long test drive up to full operating temperature to locate the smaller hard to find leaks. Bear in mind that there are so many areas that can leak, and so few that are easy to actually view with the naked eye, that leak detection can involve multiple rounds of detection and repair. It can be incredibly difficult to be sure you’ve found them all. Don’t get discouraged! Every little bit helps.

I would be surprised if the areas that were resealed 300 miles ago are leaking but it has happened before.   On the 964 and 993 engines, every one I have seen eventually leaks from the valve covers, the timing chain boxes, or covers.   The youngest one was only 10 years old with 17,000 miles. The material was changed during the design of the 3.4 & 3.6 engines; where aluminum and gaskets were used on the older 3.2 liter engines, now magnesium and O-rings are the new standard.   To keep the magnesium from corroding, the parts were powder coated. This is a definite improvement, but moisture works its way into the cracks between components. This process lifts the powder coating and causes the underlying magnesium to corrode extensively.   The O-rings harden, oil begins to seep, it ends up on the exhaust system and then your sweetie says, “What’s that burning odor?”   Annoying, isn’t it?

When restoring these surfaces there are three things that I recommend.   First, the channels where the O-rings sit need to be media blasted (and for good measure I usually prep the more visible exterior as well). Then, a couple coats of good quality paint are applied, taking care to block off any oil passages or threaded holes to avoid clogging them with paint. Finally, during installation, a light layer of RTV oil resistant silicone sealant is applied to fill the space in the channels around the seals and O-rings.   The sealant not only keeps the oil in, it also helps keep moisture out of the cracks. The securing studs and nuts should not normally leak or seep but they do. I seal these too.

Resealing the power steering pump drive sprocket seal is tricky.   Your former mechanic is right about removing the motor.   Information in my data bases agree with him. However, that is not how I would do it.   If you remove the passenger’s side heater box, you can remove the aluminum casting which holds the seal and O-ring for the power steering pump drive.   This method will save hundreds of dollars alone. Corrosion is almost never a problem with that area since it is aluminum.   When the casting removed and the area exposed, you can more easily see the power steering pump and determine what is actually leaking.   While you are in there, preemptively replace the crush washers that seal the hose fittings.

On the AC issue, R-12 Freon is getting hard to find and very expensive too.   Shops that service older classics have this, but it’s getting more expensive by the year. You may want to consider changing the system over to the less-expensive R-134, but that’s a different forum! The place to begin is with a test of pressures and inspection for wetness around the O-ring seals where rubber hoses meet the metal components.

A hard to find slow leak that is common to these models is often found at the filter/dryer which is located in the left front wheel well…hiding behind the inner fender liner!   Assuming that you have no obvious leaks, have the system charged, look again for leaks, and cross your fingers. This might take a few tries. Systems that have been dormant for years will often leak just after a fresh charge since seals and O-rings can shrink from lack of use. It is a challenge to keep an older AC system working reliably but for me, I gotta’ have it! There is nothing I like better than driving my Porsche with the top down on a hot summer day with a cool breeze in my face, stereo blasting.

Yes you face some challenges and potentially expensive repairs.   That is always tough when you just want to drive and enjoy your car. You are a fine gentleman for putting the car in top shape for your relative. But once it is cool again, not smelling, nor dripping oil, I bet that you will think twice about letting it go.   Remember the joy your felt when it was fresh and new?   You can have it all again. MC