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Date: Tue, 19 Jun 2007 08:25:21 +0100
From: "Tomnospamtech" <>
Subject: Re: Anyone diagnose this?

"Véritable Rosbif" <> wrote in message news:IJKdnSqpkOJ_P-vbnZ2dnUVZ8vSdnZ2dnospamom... > > "Véritable Rosbif" <> wrote in message > news:xt-dnS0xw8z6GOvbnZ2dnUVZ8sKlnZ2dnospamom... >> Saab 9-5 [2.3-litre petrol] low-pressure turbo. 110,000 miles, >> replacement >> turbo at 70,000. It has started blowing off blue-ish smoke from the >> exhaust >> when changing up 2>3, 3>4 and 3>5. It's not worse when driving 'hard', >> and >> happens on even the gentlest of changes. No difference if the engine is >> cold or hot. As the revs drop for the change, there's a small billow of >> smoke. It doesn't do it if you by-pass 3rd gear, and it doesn't do when >> changing down, as the revs increase. Any ideas of its cause? > > Asking this question elsewhere has got the quick response of "rings > possibly, but more probably valves and/or valve-guides". If so, is this a > time-consuming and complex [that is to say, expensive] job on the Saab > engine? >The reason that the smoke happens on upchange is that the turbo is spinning >at a fairly constant speed, Thus pushing oil in the turbo housing out into >the exhaust system, missing third gear allows to turbo to slow somewhat and >the boost pressure is lower, therefore less or no smoke. If it were piston >rings or valve stem oil seals, smoke would appear after a period of overun >when the throttle is reopened slightly. There are three main causes of oil in the turbo housing, Most likely is the check valve from the cam cover to the throttle body is not working or the hose is split or the bung in the cam cover is a poor fit and or poor crankcase ventilation caused by split or collapsed hoses. There is now a new type of mod kit to rectify this problem. There is a modified bango bolt that fits to the turbo coolant pipe where it fits to the side of the cylinder head to increase the velocity of water flow to the turbo thus keeping it cooler, preventing the crystalisation of oil in the housing which causes oil build up inthe housing. This should have been done when the turbo waas swapped. The other possibility is a stuffed turbo.......... regards, Tom, Saabtech.

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