speaking of sludge . . .
I, like many others on this forum, perform an oil and filter change every 5K. It’s an easy number to remember, and I rotate my tires at the same time, in addition to checking out the brakes, hoses, belts, etc.
Anyways, this time around I also resealed the engine oil sub-pan and changed the o-ring for the oil level sending unit, because it was seeping. On this engine, you have to remove the sub-pan to gain access to that o-ring I mentioned
I might add I had absolutely no trace of sludge in the engine. Considering I had the sub-pan off, I had a pretty good look at the innards of the engine.
Even though this particular car calls for oil changes every 10K, I do them every 5K. When I had that sub-pan off, I had visual confirmation that I’m doing the right thing.
Oil is cheap. Installing another engine, even it’s cheap and from the junkyard, is not.