Case Studies

Porsche 911 / 996 Coolant / Water Pump Failure and Correction

Atlantic Motorcar Shop – Porsche 996 – Coolant Leak, Water Pump Bearing Failure

No, that’s not a green icicle in the photo; rather, it’s a small stream of coolant coming from this Porsche engine.

Tech Findings

One of our AMC Service team members, Dylan, found and documented this interesting failure yesterday. Although it is on a Porsche, it is pretty instructive to what a water/coolant failure looks like in almost any car.

Signs and Symptoms

Fortunately, the client wisely shut down the car and had it towed in before any engine damage occurred. A rather catastrophic support-bearing failure of the engine coolant pump impeller at 50K miles, occurred without warning.

Failure Mode

If you follow the photo, you can see where the pump pulley has worn through the left side of the pump case, cutting a nice curved slot for about 3 inches. The failed bearing allowed the pump pulley to cock out of alignment, and the drive belt tension pushed it against the aluminum base, cutting a grove right through and creating a substantial coolant leak.

One always wants to determine the cause of any failure; parts do wear out by nature of mechanical systems, but something that should not fail, or fails catastrophically, deserves a second look with an eye to prevention. On the engine coolant pumps on most engines, the pump impeller shaft is supported by a sealed roller bearing.

This bearing is lubricated for the life of the pump, but over time, the rubber seal that separates the bearing from the engine coolant can start to leak, allowing coolant to seep into the bearing, washing out the lubrication, and causing scoring and corrosion. The bearing eventually fails like this one, and often the bearing failure is the first sign of the pump problem unless coolant comes out of the water pump seal or weep hole.

In this case, there was little that could have been done to prevent the problem, or even diagnose it early, as no external coolant leakage was present. You’ll usually note coolant seepage at fitting, hoses, and pumps, by the build-up of a crusty substance around the source of the leak; this is a solid red flag. But in cases like this, there is little, other than proactively replacement of the pump, that could have been done.

Being a rear-mounted engine, with the engine radiator conventionally mounted in the front of the car, the 911 series has some very long coolant pipes and hoses; (see the diagram), all of which should be inspected during this service. Also, because of the length of the cooling system pipes and hoses, is very important that a proper and thorough bleeding procedure is done to remove any and all air from the system. Ideally, a vacuum bleeding machine should be used for service and filling of the system.

Correction will be the removal of the failed pump, and cleaning the engine and coolant system passages from any metal filings. Replacement of the coolant pump, replacement of the thermostat (right in the same area), replacement of the drive belt (soaked with coolant), then flush, fill, and bleed the air from the cooling system.

An Ounce Of Prevention
If you’re an Atlantic Motorcar client, we’re going to be keeping an eye on this for you.
If you’re not, make sure it gets checked, kind of like that old bromide about voting, “early and often”. 😉

Our Goal For You and Your Car
Our goal is to save you money, not spend it. This is why each and every car that we service gets a free Courtesy Maintenance Inspection during its first visit. Our goal is to let you know about the small problems before they become big ones. Right now, we have a number of customer cars with well over 200,000 miles, and several approaching 300,000! And these cars are not just limping along – most look and drive pretty much the way they came out of the showroom.

Proper maintenance is an investment in the life of your vehicle.
Knowing, not just doing, but actually knowing and understanding the difference, makes all the difference.
Be sure your car is properly loved, our professionals will attend to both you and your car’s needs.
Atlantic Motorcar…Extraordinary Service for Extraordinary Cars, just a phone call away, (207) 882-9969.


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