Mad Sludge

[scatgo]

Have the heads of of my 1999 Forester and I can see lots of a black tar like goo all over the top of the heads. I can clean this off no problem because the heads are off but i would guess the inside of the engine looks just as bad. Are there any oil additive you guys would recommend to remove heavy sludge deposits from inside a engine. And what would cause such a situation? Maybe a bad PCV valve?

 

Thanks 

 

Chris

[montana tom]

Tar like goo on top ? you mean the outside of the head near where the manifold bolts on ?  Or inside where the valves are ?  If you mean under the valve cover at what would be the bottom , then don't worry too much . Oil pools there and does not easily flow away.... the heat bakes it into goo.   

Edited February 21, 2015 by montana tom

[ccrinc]

My gut says the engine oil hasn't been changed regularly and that the oil being used is one with high sulphur and/or paraffin content.

Good ol' Rislone will help clean that up.  Do an oil change (obviously, at this point, you have to), put in 1/2 qt. Rislone to 3.5 qts.+ of cheap oil.  Run for about 50 miles, then do another complete oil change with new filter.  Side effect: helps re-expand withered internal seals.

 

It's old school, but it still works!

Edited February 21, 2015 by ccrinc

[keith3267]

If it is the area under the valve covers, then it is possible that it won't be in the rest of the engine.  The main area of concern would be the oil drain back passages.  This is where the oil drains from the heads back into the pan.  If this gets blocked up, and it will if the sludge problem gets too bad, then the oil will get trapped in the top of the head.  When that happens, some will get sucked into the combustion chamber through the valve guides, even if the valve seals are good.  You could also suffer oil starvation when the pan goes empty.

 

The sludge builds up when you shut down a hot engine.  Oil stops flowing so the oil that is trapped has to absorb all the heat from the engine.  The trapped oil gets much hotter than normal and begins to cook.  That makes it thicker.  Most of the time, when the engine is restarted, this thicker oil gets flushed away, but it mixes with the rest of the oil and so it causes all the oil to become a little thicker.

 

Over time, the bulk of the oil in the pan has become thicker and then during subsequent shutdowns, the remaining trapped oil starts out already thicker, becomes a goo we call sludge.  It is generally confined to the tops of the heads where most of the residual heat is dissipated.  It will build up in the oil drain back system too.

 

When I see this, it is usually because the oil was not changed as often as it should have been or an oil with too much viscosity improver (VI) was used, i.e. 10w40 or additives like STP or Lucas were used on a regular basis.  Synthetic oils do not sludge as easily as conventional, but they will if the oil change interval is stretched too far.  Group III synthetics can go for 7.5 to 10k, Group IV can go for 15k or more.  6K is about the limit for conventional oil, but 5k would be better.

[Fairtax4me]

If its hard crusty stuff like chunks of asphalt, pull the oil pan and make sure the pickup tube screen isn't clogged with the same crud. Have seen lots of clogged pickup tubes cause bearing failure on other cars because of this.

The other thing you should do is pull all of the PCV and breather hoses off and make sure they're clear. Make sure the PCV valve is clear (replace it if its old) and make sure the PCV port in the manifold is clear.

Make sure to clean the valve covers thoroughly. Might even consider having a machine shop hot tank them to make sure the breather baffles are clear.

[scatgo]

Thanks

[keith3267]

I don't think I would hot tank an aluminum head, I have done that on cast iron heads and one time, it cracked even the cast iron.  I would only clean it mechanically.  Thats scraping, brushing and Calgon detergent.