1992 Toyota Previa van, replace head gasket
The toyota previa uses a formed silicone gasket for the valve cover and the cover is held in place by metric shoulder bolts ( 10mm). The valve gasket leaks because you can't get enough preload on the bolts to re-seat the old gasket when it gets old and shrinks. The shoulder bolts only allow you to tighten the gasket enough to seat the shoulder on the bolt. If you continue to torque down the suspected bolts, you will snap the bolt off ( don't ask me how I know this ). You can either 1.)replace the old gasket with a new one or 2.) remove the existing bolts around the leak area and put in new metric bolts that do not have a shoulder. You may want to put in a small sleeve into the existing bolt hole but shorter than the thickness of the valve cover to account for the smaller diameter bolt. You can now torque down the bolt and get enough preload to seal the valve cover without removing the old gasket. Make sure you use a torque wrench ( in-lbs) or be very careful not to snap these small valve cover bolts.
Update (guyinseattle) - Valve cover leaking oil again. I took the valve cover off and added a bead off silicone sealant around the entire periphery and let it sit for 5 minutes to cure. I then installed the valve cover and tightened the bolts finger-tight to squeeze out the silicone and let it set. After 60 minutes, I tightened the valve cover per specification. No leaks so far (Sept 2016 - 1991 Previa with 360k miles so far)
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Our family -- same problem. I have a '91 (435,000 miles), dad's '95 (160,000 miles) both leaked almost profusely. There are 2 major reasons for these leaks. 1) As mentioned above, the valve-cover bolts (actually 6mm - with 10mm head) are too long after years of pulling the gasket tight. a couple washers under each will get you on the 'road to recovery' with this issue. 2) Next if not replaced with the valve-cover gasket, replace the distributor O-ring. This is more easily done at time of VC gasket replacement. And, "yes", use the Toyota silicone. gasket sealer. NOTE: It is ABSOLUTELY recommended that you DON'T use a heavier grade oil, northern climes or not, than that specified (5W30). See (Search: Ferrari Chat Oil)
You will need a new head the block is bomb proof consider a second hand engine also consider the cost and value of the car
For leaking head gasket it has to be replaced.For head gasket leaking and other troubleshooting,there are help links provided.Its suggested to click the link below and go through the troubleshooting procedure to confirm the issue :-----
Leaking head gaskets?
http://schematicsdiagram.blogspot.com/2011/12/leaking-head-gaskets.html
-----------Water in engine oil? http://schematicsdiagram.blogspot.com/2011/12/water-in-engine-oil.html
-----------How to replace head gasket on car?
http://schematicsdiagram.blogspot.com/2011/12/how-to-replace-head-gasket-on-1994.html-------------
How to know what is faulty Cylinder head or Head gasket?
http://schematicsdiagram.blogspot.com/2011/12/how-to-know-what-is-faulty-cylinder.html
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Can I just replace Head Gasket on 1991 Buick Century?
http://schematicsdiagram.blogspot.com/2011/12/can-i-just-replace-head-gasket-on-1991.html
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Location of Head Gasket ?
http://schematicsdiagram.blogspot.com/2011/12/location-of-head-gasket-on-1994-grand.html
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HOW TO REPLACE A HEAD GASKET
http://schematicsdiagram.blogspot.com/2011/07/how-to-replace-head-gasket.html
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How to replace Exhaust Manifold?
http://repairhelpcenter.blogspot.com/2011/11/how-to-replace-exhaust-manifold-on.html
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How to replace Intake Manifold?
http://repairhelpcenter.blogspot.com/2011/11/how-to-replace-intake-manifold-on-acura.html
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How to replace Cylinder Head ?
http://repairhelpcenter.blogspot.com/2011/11/how-to-replace-cylinder-head-on-acura.html
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Is it Easy to replace head gasket?
http://schematicsdiagram.blogspot.com/2011/12/is-it-easy-to-replace-head-gasket-on.html
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Should I only replace head gaskets or complete head gasket assembly?
http://schematicsdiagram.blogspot.com/2011/12/should-i-only-replace-head-gaskets-or.html
---------This will help.Thanks.
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To me this sounds like you actually mean that the valve cover gasket might need to be replaced which is far easier and less expensive than replacing a head gasket. If this gasket is leaking you may get oil dripping out of the engine as you say.
What symptoms have you observed other than the external oil leak that lead you to believe you need to replace the head gasket?
It is wet in that area also I can see from above the oil pan cover
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