Found oil leak when changing thermostat

SpeedUp · Nov 16, 2018

Installed a new thermostat, thanks again for the advice from my previous thread. When I was looking at things under the hook more closely I decided to remove the alternator because I saw oil leaking.

The o-ring on the old thermostat was almost 2x too big. Seriously, it would not even fit into the groove, I have no idea how it wasnt leaking bad.

After I removed the alternator I snapped a few pics, how bad does this look? Where does it look like its coming from? Does it look like some coolant mixed in?

Mooseman · Nov 16, 2018

Could be the valve cover gasket. And to replace that, you have to remove the intake manifold. If you decide to not fix it, cinch up the intake bolts while you're there.

SpeedUp · Nov 17, 2018

Thank you Mooseman, I will check that out.

mrrsm · Nov 18, 2018

On the problem with the Valve Cover "O" Ring Style Gaskets held in with "Trapped Fasteners".... they tend to flatten out severely on High Mileage Motors... so avoid using more than 87 Inch Pounds of Torque when re-tightening them. If they have REALLY flattened enough to allow the Cover to make contact with the Engine Head... No amount of Cranking Down on them will make any difference.

And while you have easy access to the lower bolts of the Intake Manifold... please take note of the image of this pair of Intake Valve Ports from my 2004 Donor Engine during tear Down. You can see how much of the Re-Cycled, ingested Motor Oil coming from the PCV Rubber Elbow feeding into the Resonator Box just above... winds up collecting and contaminating inside of the the Intake manifold. You can see that the color and texture of that Black Mung Oil looks an awful lot like what is right there underneath the IM Ports showing in your photos.

So if those similarly "Trapped" Fasteners get real loose... that Dirty, Black Oil could also be oozing out from the interface in between the Aluminum Engine Head Intake Port... and the Black Plastic Intake Manifold that... coincidentally... Shares the same style "O" Ring Gasket as the Valve Cover. Again... Only tighten these down to 87 Inch Pounds. :>)

mrrsm · Nov 18, 2018

To complete the On Topic Subject of the Cause, Origin ...and Cure for this Problem:

Back when I was designing and building “The Franken-Oiler Machine” as a Functional Electro-Hydraulic Engine Pre-Oiler…

http://s557.photobucket.com/user/60dgrzbelow0/library/ENGINEPREOILER?sort=3&page=1

… I also modified a GM 4.2L LL8 Valve Cover to sport some Glass “Viewing Windows” on top of the Oil Vapor Collection Chamber in the cover so I could observe the performance of the Valve Train in real time as the Fresh Motor Oil was being distributed under pressure by the Pre-Oiler Machine.

At that same time… while removing the Old “O” Ring Style Valve Cover Gaskets and replacing them with a New Set... I could NOT believe just how much they had all flattened out over time… so much so in fact that when viewed in profile ...you could see why GM only required a mere 87 Inch Pounds of pressure to slightly squash down the Gaskets… as they literally completely suspend the Valve Cover up and off of making direct contact with the flat flange surface of the Aluminum Head floating on those “O” Ring Style Gaskets. Take Notice that even the “Trapped Fasteners” themselves...are completely isolated from ever making Direct Contact with the Valve Cover Hold Down Flange via Black Rubber Grommets.

But with time, temperature and the wear & tear caused by Engine Heat and Vibrations… they eventually 'Give Up The Ghost' and after losing their “Plump”… they fail to separate the actual Composite Nylon Cover-Lid from making contact with the Aluminum Head. By then… Hot Motor Oil has long since migrated from the inner Valve Cover Gaskets down inside of the Spark Plug Wells...where it can cause all sorts of mischief.

Likewise ...this very same phenomena occurs with the Plastic Intake Manifold… that oddly bounces and jostles up and down due to the “Teeter-Totter” of the weights of the Throttle Body on one side… and the PCM bolted up on the opposite side. In time… ALL of those Gaskets Flatten Out and Fail...and this results in the Fasteners loosening, too as the Gaskets give way. Here are some very illustrative images of what these Gaskets look like in profile… when Brand New: