This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.
One of the most important elements of your 911's exhaust system is the heat exchangers. Not only do they funnel the exhaust out from the engine, but they also provide heat for the interior of the car. However, the heat exchangers take quite a lot of abuse, and they have a tendency to be one of the first components on the car to rust. Salt, water, and other debris can easily get washed up onto the bottom of the heat exchangers causing them to begin to rust.
In addition, oil leaks from the engine can drip down on top of the heat exchangers, causing them to smoke when the car is running. Oil that seeps down onto the exchangers can also cause dirt and grime to build up on the inside. When the car is warm, and the heat exchangers hot, this grime and oil heats up and smokes. This smoke is often channeled right into the cockpit of the car. This smell of burning oil is very reminiscent of older cars of this type, and is sometimes called "that air-cooled car smell."
The only way to rid yourself of the air-cooled problems is to fix all the oil leaks on your engine (covered in Pelican Technical Article: Fixing Common Oil Leaks) and replace your heat exchangers with brand new ones or good quality used ones.
Brand new heat exchangers from the factory can be quite expensive. New exchangers for a 911SC list for more than $1000 each. The older style heat exchangers can actually be had for less, but they are still very pricey indeed. A good compromise is a set of used exchangers that have come from a relatively rust-free environment like California. In some cases, it may be difficult to find a really good set, but if you keep scouring the classified ads from Porsche sources around the world, you should be able to find some.
Another alternative is brand new stainless steel heat exchangers from a company called SSI. These exchangers will most likely outlast the life of your car. Made from 100% stainless steel, these are guaranteed to never rust and never corrode. Occasionally you can find a set of used SSI heat exchangers, but it's not very common. These exchangers are built so tough that they are usually snatched up really quickly by people looking for them. A typical used set sells for about $500, which is about half the cost of a new set.
Removing your heat exchangers can sometimes be a very risky task. The rust, combined with the high heat of the cylinder heads, can temper the studs on the heads to the point where they have a tendency to break off when you try to remove the heat exchanger nuts. It's very important to use plenty of WD-40 and let the nuts soak for a few days before you try to remove them from the studs. Tom Woodford of Factory Tour recommends the use of a torch to heat the nuts prior to the removal attempt. The heat from the torch will expand the nuts and reduce the chance that the studs will break off. If the studs break, then you will have a very difficult time removing them from the heads. You may have to resort to EDM methods such as the one described in Pelican Technical Article: EDM Broken Bolt and Stud Removal. It's a wise idea to be very careful when removing the nuts from the studs.
To access the heat exchanger barrel nuts, you will need to have an angled 13mm wrench and a special heat exchanger barrel nut removal tool. The removal tool is basically a very long 8 mm Allen hex key with a socket end on it. You can remove these nuts by placing the removal tool through the access holes located in the heat exchangers. The nuts are a small, special type of barrel nut that will fit through the holes in the heat exchangers.
When reinstalling new exchangers, make sure that you use new exhaust gaskets at the heads, and at the exhaust pipe end. It's wise to coat the nuts with a little bit of anti-seize compound in order to prevent them from rusting and sticking together.
While you have the heat exchangers off, take a look inside the heads and see if you can see anything that doesn't quite look right. Lots of black carbon built up on the outside of the valves and the chamber is an indication that the mixture might be set a little too rich. One cylinder looking different from the others is also a sign that there is something wrong. In general, all the cylinders and their exhaust ports should look similar. If you have any doubts, you might want to take the car into your mechanic for an expert opinion.
Truly a sight to be seen, here is a picture of a brand new 1965-74 stainless steel heat exchanger. These exchangers bolt up to a dual-inlet muffler, and are the type of exhaust that many people place on their 1974 and older 911s. Stainless steel heat exchangers for the 1978-1989 911SC and Carrera are available as well. Stainless steel heat exchangers keep their value and are a worthy investment. A used set of heat exchangers can simply be cleaned and bead blasted, and they will look and perform as good as new. They are basically indestructible.
Good, rust-free heat exchangers can be difficult to find. This one is for a 911SC, and is one of the best examples around. The 911SC and Carrera heat exchangers, surprisingly enough, are identical for both left or right. Finding a really good used pair can be difficult, but well worth it when you consider the cost of new ones, or the cost of stainless steel heat exchangers.
The heat exchangers are attached and secured to the car by their connection to the heads. The top arrow points to one of the nuts that bolt the heat exchangers to the heads. The lower nut points to the access hole in the heat exchangers that must be used to remove the small barrel nuts that are difficult to remove with a regular tool. Be careful when removing these nuts. The heat from the heads combined with rust can lead to a situation where the stud breaks off when you try to remove them. If this happens, then you will have a very difficult time removing the broken stud from the head.