1997 Chevy Lumina

  • 6 CYL
  • FWD
  • 196,500 MILES
Occasionally, in the past, my "check engine light' would come come on, I would get it diagnosed at Autozone as a EGR valve problem. I would clean out the carbon deposits, put it back in place and the problem would be resolved. There was never a problem in engine performance.
This last time, when it was again diagnosed as the EGR valve, I routinely went to clean it, but it was filled with a muddy sludge that I never saw before. Again, there is no problem in engine performance. What is this stuff, and does it represent a bigger problem?
Do you
have the same problem?
Thursday, November 19th, 2009 AT 11:33 AM

1 Reply

With the 196500 miles, problem with carbon deposits is common issue
As the miles add up, motor oil loses viscosity and gets dirty. The oil no longer has the same viscosity range it had when it was new, and it contains a lot of gunk (moisture and acids from combustion blowby, soot, dirt and particles of metal from normal wear). You can't really tell much about the condition of the oil by its appearance alone because most oil turns dark brown or black after a few hundred miles of use.

The oil filter will trap most of the solid contaminants, and the Positive Crankcase Ventilation (PCV) system will siphon off most of the moisture and blowby vapors, if the engine gets hot enough and runs long enough to boil the contaminants out of the oil. Even so, after several thousand miles of driving many of the essential additives in the oil that control viscosity, oxidation, wear and corrosion are badly depleted. At this point, the oil begins to break down and provides much less lubrication and protection than when it was new.

If the oil is not changed, the oil may start to gel or form engine-damaging varnish and sludge deposits. Eventually this can cause your engine to fail! Oil sludge can damage engine bearings, piston rings, cylinder walls, valve guides and lifters.
Was this
Saturday, November 21st, 2009 AT 2:26 PM

Please login or register to post a reply.

Recommended Guides