Oil discussions will continue to be the bane of forums such as this.
Reciprocating engines' oil is supposed to be black after a while. Give this a shot... change it, wait 1,000 miles, then look at it again. Heck, look at it after 500 miles. It will be dark, prolly nearly black.
The true test of an oil's capabilities comes in laboratory analysis. This will yield such things as metal content, additive breakdown, etc. Nowadays, folks are going amny miles longer on each change, just sampling the oil at different intervals.
The problem with this is that for the average consumer, the cost of multiple analyses is more than changing the oil (unless you are talking synthetic). But if you have access to free samples, say thru work or a lab friend, take advantage of it. You will be surprised at what you find out.
About 15 years ago, I met a man who was on a personal campaign to promote synthetic oil and extended usage intervals. He was using Mobil 1, changing his filter every 25,000, and the oil every 50k miles. When I talked to him, he had over 150k on the car, and it was stil going strong. His goal was 300-400k using that schedule. I wish I could have talked to him later, and see what he concluded. His oil samples were coming back fine every time, he said.
Personally, I am for extended intervals. It is cheaper, and is better for the environment. Until someone can show me where a car was properly cared for & driven, and the extended interval caused premature wear or damage, I am all for it.
Turbine engines are a different animal than recips, in that the oil never contacts the flame areas of the engine, but guess what the drain interval is on a turbine engine?
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Never.