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Evil, thy name is Sludge Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Wed, 13 May 2009 11:12:29 In Reply to: Where does oil pressure come from?, EricG, Wed, 13 May 2009 08:50:19 Members do not see ads below this line. - Help Keep This Site Online - Signup |
A common cause for a sudden (and catastrophic) loss in oil pressure is sludge. This is the, well, sludge, that accumulates in the oil pan. A chunk of it floats up and covers the oil pickup screen. Cover enough of the screen, and the oil pump can't pull oil, sucks air, and then oil pressure drops to near nothing.
Sludge has become more prevelant in recent years. In the interest of improved fuel economy and performance, engines run hotter and with tighter tolerances, stressing the oil. Crankcase ventilation flow has been reduced, to improve emissions, but this can overheat oil. Manufacturers are going to longer and longer oil change intervals. Sludge accumulates, and unless actually cleaned out, just builds up.
The 9-5 had a major sludge issue, partially due to low crankcase flow, mostly due the exhaust running right under the oil pan. The 9000 had sludging issues, primarily in the '90s. Part of that was due to a lot of lease cars with spotty maintenance. But you can change the oil frequently and still get sludging.
If you drop the oil pan, you can see if the oil pickup screen covered with gunk, you've found the problem. The 9000 oil pump was very robust, and rarely failed. The oil pressure relief valve spring could fail. But I'm betting on sludge.
Sludge isn't just a Saab issue - most cars since the mid 90's have a sludge issue to one extent or another. The vaunted Toyota had a major issue with it.
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