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Just finished replacing my valve cover gaskets on my 400 with 150,000 miles. While I had the valve covers off, I decided to clean them up as best I could. I noticed lots of caked on sludge...almost like the oil had been burnt. I spent hours cleaning them.
Is this normal? Any recommendations on preventing this in the future? Are there any additives that will clean areas I couldn't get?
no matter what anybody says, old engine or new engine, sludge is not normal.
First additive that comes to mind is seafoam. There are some others out there, but I've only used seafoam. Oil drain is very dark after running it through, so i guess it's doing its job.
Make sure everything is NICE and tight. If it's not, and that sludge you cleaned off was actually helping seal things up, cleaning it up and breaking it down might not have been the best for the engine. Unless you did a complete engine breakdown/cleaning/rebuild, then that's another story. If seafoam is started early and done every so often, I could see the benefit, but when you first start it on a high mileage motor, you're breaking down deposits that have been sealing the motor up on the inside, and sending those deposits everywhere. All you have to do is read about it.
I seafoamed my SC4 when I had it, and it had over 150K on it. She blew some nasty smoke out (that was normal), and after an oil change, and sparkplug change, she hadn't really changed that much to be honest. Some folks will swear on the stuff and tell you it's a night and day difference. However, when it comes to a high mileage engine, as they say "if it ain't broken, don't fix it".