Slipstream - February 2014

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Tech Corner: Too Much of a Good Thing By Ed Mullenix, Tech Session Chair Dr. T has a beautiful blue ’99 Carrera that is now on water pump #7. Sadly, the water pump on the Boxster, 996, and 997 cars is not the most reliable part of the design. The life expectancy of the water pump is unpredictable. I have customers with well over 100K miles on their cars and they still have the original pump. I also have some that have had to replace the pump at as little as 30K miles. Dr. T’s car has around 60K miles at present. Not nearly enough miles to expect seven pump replacements. His first pump replacement was about five years ago at about 40K miles. That pump lasted slightly longer than a year. The number three pump went about a year and a half later. Dr. T. Decided to take his Carrera to a different shop when #3 started leaking. Pump #4 lasted less than a year, as well as #5. The good Doctor brought his car to my shop and was concerned about its chronic water-pumpitis. I would have started looking for some anomaly with the cooling system after the third pump started leaking. True, the pumps don’t last all that long, but three in a year should have caught someone’s attention. Modern cooling systems use a 50% mixture of anti-freeze and water to protect the engine from not only frigid temperatures but also to improve the boil-over protection. To further improve the boil-over protection, the cooling system is provided with a pressure cap (used to be called a radiator cap when it sat on top of the radiator). In 1977, when Porsche introduced the wildly popular 924, the pressure cap maintained one bar (14.5 psi) of pressure on the cooling system. The pressure caps on the current cars maintain 1.5 bar (22 psi). This pressure raises the boiling point of the coolant to about 265 degrees F. The components of the cooling system, i.e., pump, reservoir, and radiator, are designed to withstand that pressure. The lonely pressure cap sits on top of the coolant reservoir. It’s pretty reliable and doesn’t get much attention, and therein lies the problem. When a car comes in for servicing and the coolant level is low, standard procedure is to pressure test the system and look for a leak. Apparently, many of my colleages don’t test the pressure caps. When I tested his pressure cap it went to 50 psi, the max pressure on my gauge. His pressure cap never vented any pressure, so excessive pressure would develop, with the resultant pump leakage. I am surprised that he didn’t have other components fail as well. Thinking that all was well and I had cured the water pump issue, pump #6 that I just installed started leaking; it didn’t even make it out of the shop. No pressure problems this time -- just a pump that was made on a Monday morning after Oktoberfest. I SO enjoy a challenge! More Too Much of a Good Thing Porsche recommends Mobil 1 synthetic oil be used in their engines. The viscosity of factory-fill is 5W30, an acceptable oil for most climates and uses. Bring a Porsche to Texas in August, take it to the track, and see what happens to the oil pressure and ultimately, the engine. Oil is a cushion that separates the metal of the crankshaft from the metal of the bearings. I like to compare oil to one’s shoes. I can walk barefoot on pavement. I prefer to wear running shoes if I am out running. I wear hiking shoes when I go hunting. I don’t run barefoot or in hiking shoes. Bill, a 996 customer of mine who suffered an engine failure a while back, is keen on doing some of his own maintenance. After the engine rebuild, I recommended he use Valvoline VR-1 20W50 racing oil, since he tracks the car a lot. The parts store he goes to didn’t have VR-1 20W50, although they did have VR-1 straight 50-weight. That’s the oil he installed when he changed it. The car performed great last winter and this past summer. This year when it got cold, the 996 developed a running problem. Bill lives in Sherman, where it is usually ten degrees or so colder than it is here. I brought the car into the shop and ran the test protocol. Nothing, no component or sensor issues. Great compression, ran great. I left the car parked outside overnight. The next morning when I drove the car, it started up fine and ran about a block when the engine died. I had to wait about a minute before it would restart. It would crank over but would not start unless I waited a minute. Thinking it must be an intermittent sensor issue that only manifested when it was really cold, I replaced the engine coolant temp sensor, 26 <strong>February</strong>
Since 1971 Providing personalized service on all Porsche automobiles. • Complete servicing and repairs on all air or water cooled models • In-house machine shop • M96/M97 reconditioning • Performance and track mods 2530 Tarpley Road • Suite 700 Carrollton, Texas 75006 (972) 417-0997 parked it outside again, but the next morning showed the same result -- it died after driving about a block. If I let the engine warm up a bit before driving, it ran fine. Sitting in a chair in the shop, staring at the uncooperative 996, I pondered what it would be like to be a lottery winner instead of a mechanic. Then I had the “light bulb moment.” The M96 engine has hydraulic valve lifters. It also has valve springs with reduced tension (in order to improve fuel economy). I called Bill and asked him what oil he used when he changed it. He admitted to using the straight 50-weight because he couldn’t get the 20W50. I changed the oil in Bill’s 996, using 20W50. The problem went away. With the straight 50-weight, the oil was so thick that when it was cold, it would allow the lifters to hold the valves off of the seats, with resultant compression loss until the engine got warm and the oil thinned a bit. I maintain some club racers and serious track cars that use straight 50-weight oil. Those cars don’t sit outside overnight so the 50-weight oil isn’t a problem. Oil viscosity -- a little is good, more is better, but too much is NOT just right! 27
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