Pelican Technical Article: Fixing Common Oil Leaks Wayne R. Dempsey
Time: 12 hr
Tab: $40-$200
Talent:
Tools:
Need full set
Applicable Models:
911 (1965-89) 930 Turbo (1975-89)
Parts Required:
New gaskets, o-rings, valve covers
Hot Tip:
Replace all the seals that might leak when you have the engine out of the car.
Performance Gain:
No more oil leaks!
Complementary Modification:
Installation of Turbo Valve Covers, Installing collapsible oil return tubes.
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.
Check out some other sample projects from the book:
One of the most frustrating aspects of owning an older Porsche is the inevitable existence of oil leaks. The 911 engine in particular has a lot of different seals and connections that can often deteriorate with age, resulting in a large amount of oil leaks. Unfortunately, some of these leaks cannot be fixed without the engine removed from the car, or the fuel injection removed from the top of the engine. Its a wise idea to start with the leaks that are easiest to fix, and then move onto battling the harder ones later.
Perhaps the easiest oil leak to fix is the one involving the valve covers. Early covers manufactured out of magnesium had a tendency to warp and leak past the valve covers seals. The easiest solution to this problem is to replace your valve covers with 911 Turbo valve covers. These covers are manufactured out of aluminum and reinforced to reduce the warping that is often associated with the magnesium covers. For more information on installing the Turbo Valve Covers, see Pelican Technical Article: Upgrading to Turbo Valve Covers.
Some of the most common oil leaks cannot be fixed, unfortunately, without removing either the engine or the fuel injection. Some of the components and areas most susceptible to leaking are located in the front of the engine near the flywheel and are completely blocked by the fuel injection components. One such spot is the location where the crankcase breather hose is connected. Tightened around its fixture with a hose clamp, this hose can sometimes come loose or split, spilling oil all over the top of the engine. The solution is to replace the hose and retighten it with a new clamp. The crankcase breather cover where the hose mounts is also a problematic area for oil leaks. This small cover for the top of the engine has a gasket that seals it from leaking. Replacement is simple: remove the cover and install the new gasket with a slight bit of gasket sealer.
Right near the crankcase breather hose is the oil pressure warning lamp switch. Not only does this component often begin to leak out of its housing, but it also can leak at the connection to the case. The fix is to replace the entire sender (about $10). Make sure that the new one is tightened properly in the case, and also use a new metal crush washer gasket. Be careful not to over tighten the switch, as this may ultimately cause its housing to separate and leak oil. This can sometimes be blindly repaired without removing the engine or fuel injection - even though you can't actually see what your doing. On early cars, the oil pressure sending unit which also often leaks, was installed in this location.
Directly adjacent to the oil pressure switch is the thermostat, which controls the flow of oil to the oil cooler. The thermostat has an internal o-ring which seals itself against its housing and prevents oil from leaking out across the top of the engine. The thermostat can see somewhat high oil pressures, so it is especially prone to oil leaks around this seal. To repair the problem, simply remove the two 10mm nuts that hold the thermostat to the case. Gently pry up the edges of the thermostat with a screwdriver, replace the o-ring, and then reinsert into the case. It should be noted that all o-rings when installed should be liberally coated with fresh, clean motor oil prior to installation.
Located in the same general area is the oil cooler. The three seals that mate the oil cooler to the engine case also have a tendency to become brittle and leak. Replacement requires the removal of the oil cooler: a task that can be accomplished with the engine in the car. You need to disconnect the oil line that mates to the oil tank and loosen up the surrounding sheet metal in order to gain access to the three nuts that mount the cooler. Wet the seals with a bit of fresh oil when you remount the cooler. If you suspect that the oil cooler itself might be leaking, then it may be a wise idea to have the oil cooler pressure tested for leaks at your local machine shop.
Connected to the oil cooler is an S-shaped hose that attaches to the oil tank. This rubber hose can develop cracks and leak over the years. Its best to replace this hose if there are signs of weakness in the rubber. The hose is simply connected with two hose clamps, and easily removed. Make sure that you empty the oil from the engine and the tank prior to disconnecting this hose, or you will have a mess on your hands. The other oil lines than run under the engine and mate to the tank have a tendency to leak as well. Carefully inspect all lines for oil leaks, cracks, and breaks when you are looking under the engine.
Underneath the valve covers lie the rockers, which have been known to occasionally leak. The factory originally didnt supply a seal for these rockers. Instead, they use a compression fit to seal the oil inside the internal cambers. The Porsche factory workshop manual summarizes the design quite well:
The rocker shafts are designed so that tightening of the Allen screw compresses the two cone-shaped pieces (nut and bush) against the coned ends of the rocker shaft and spreads the ends. As the rocker shaft ends spread the rocker shaft is tightened in it bore in the camshaft housing and thus prevented from turning or axial movement.
However, this design doesnt always work too well. If the shafts or the cone-shaped pieces dont mesh properly, then there might be room for oil to seep out. A secret fix is a small rubber seal that fits into the small groove of the rocker shaft, and helps to seal the internal chamber. This part was a race-motor part that was not originally used on the production engines, but works pretty well to stop these oil leaks when installed. The part number for this rocker arm shaft seal is 911.099.103.52, and you need two of them for each rocker for a total of twelve.
Another common oil leak comes from the oil return tubes. The seals at the end of the tubes expand and contract many times over the years, and develop small oil leaks. For more information on the replacement of these seals, please see Pelican Technical Article: Replacing Oil Return Tubes, Replacing Oil Return Tubes.
At the lower rear of the engine are the cam housing covers. These are sealed with thin paper gaskets that can develop leaks if not installed properly. Replacement of these gaskets is a bit of a pain, requiring removal of the muffler, and the rear engine shelf sheet metal. For more information on replacing these gaskets, please see Pelican Technical Article: Upgrading to Late-Style 911 Carrera Chain Tensioners, Upgrading to Carrera Chain Tensioners.
On the top-rear of the engine are the camshaft oil feed lines. These lines supply the cam towers with oil to lubricate the cams and the rocker arms. These lines have a tendency to vibrate and develop leaks over the life of the motor. Replacement is an easy process, although you might have to remove the distributor in order to reach one of the fittings. Make sure that you use new sealing rings when you remount the lines. Project 16 details the installation of these lines in further detail.
Adjacent to the right cam oil line on the later cars is the oil pressure sending unit. This unit has a tendency to leak where it is attached to the case, and also from its own housing. Carefully inspect the sender, and replace it if you think that it might be leaking. Since access to the sending is fairly straightforward, it is not necessary to be cautious: dont replace it unless it is leaking. On the early cars, this unit is located towards the front of the engine compartment.
The flywheel seal is another one of those common and mysterious leaks on the 911. Unfortunately, the flywheel seal cannot be replaced without removing the engine and the clutch. For more information on the replacement of this seal, please see Pelican Technical Article: Clutch Replacement, 911 Clutch Replacement.
On the very rear of the engine is the pulley seal. In order to replace this seal, you need to remove the muffler, rear engine shelf, the motor mount bar, and the rear pulley. Removal and replacement of the seal is similar in nature to the replacement of the flywheel seal. Be careful not to scratch the outer surface of the crankshaft when you replace the seal.
Figure 1
Valve covers are notorious for leaking, especially on the 911s equipped with magnesium valve covers. If yours are leaking, replace the gaskets first. There are available silicone beaded gaskets which more pliable and supposedly stop oil leaks much better than the standard gaskets. If your oil leaks persist, consider upgrading to Turbo Valve Covers (See Pelican Technical Article: Upgrading to Turbo Valve Covers).
The crankcase breather hose mounts to the top of the engine and is sealed to the case by the gasket shown here. Replacement of this gasket requires removal of the engine or fuel injection system, and should be replaced every time that you have access enough to reach it.
The crankcase breather hose could be another source of oil leaks. It sometimes has a habit of coming loose and slipping off of its mount. Make sure that you have a clamp on the hose to secure it to its mount (shown by arrow).
The oil cooler thermostat o-ring is another source of troublesome oil leaks. Replacement is almost impossible without removing the engine or the fuel injection. Install the o-ring wet by placing a little bit of oil on the o-ring seal when you install it.
The oil pressure switch located all the way behind the fuel injection is one of those annoying $3 parts that have a tendency to fail. It is recommended to swap this part out with a new one every time that you have access to it (usually when the engine or fuel injection is removed).
The rocker arm seal is one of the best kept secrets. Not an original production engine part, this little seal fits in the small groove of the rocker arm (shown in photo), and helps to seal the shaft from leaking. Normally, the expansion of the end of the shaft in the cam towers is supposed to seal the rockers, but this sometimes fails, especially on rebuilt engines.
When the engine is out, access to the oil cooler is easier than when its in the car. The oil cooler seals are well known for their ability to spring leaks. Replacement of these three seals (two identical sized ones on top, one on the bottom) is easy once the oil cooler has been removed.
The flexible oil cam lines deteriorate over time, and spring leaks at the points where the rubber meets the hard lines (shown by arrow). These lines are generally pretty accessible from the rear of the car. The only component that might get in the way would be the distributor, which is easily removed.
This photo shows the distributor o-ring that seals it to the engine case. Although not a high oil pressure area, this seal does sometime fail. Make sure that you place the engine at Top Dead Center before you remove the distributor. That way, you can make sure that you replace the distributor into its proper position again.
The oil pressure sender can leak from its base or directly from the main unit. Replacement is easy since the unit is located near the rear of the car. Wrap a bit of Teflon pipe sealing tape around the connection to assure that it wont leak.
Underneath the crankshaft pulley is located the main shaft seal. Replacement requires removing the motor mount, the pulley, and a few other parts to reach the seal. It can be removed and pressed in similar to the replacement of the flywheel seal. This photo shows the seal as installed inside of the number eight bearing, prior to the crankshaft being installed into the engine case.
Comments: our customers car a 1974 targa seemes to be leaking oil from the center right front area we have seen it coming from what looks to be an open tube perhapes the breather the oil level in the tank seems to flucate up and down and at one point there was alot of oil in the air filter box any ideas?
March 21, 2012
Minimo
Comments: My 2.7 engine smokes when started after it sits for a few days. If I drive the car daily it doesn't smoke when started.
I removed the spark plugs and noticed one plug coated in oil.
Is the oil coming from worn out valve guides or the rocker seals? Rocker seals would be easy to install.
December 3, 2011
Check out some other sample projects from the book:
