Quote:
Originally Posted by oil pan 4
One thing I found with my summers long lubericheck tests is that air cooled engines with out oil filters were the worst as far as quickly degrading oil.
With in a few tanks of fuel the oil in the engines goes black, then 10 to 15 more tanks later the oil starts to turn to kind of a brownish color. Brownish oil tested as "very bad".
Now these were only honda GC160 engines on a pressure washer.
I'm sure they burned less than 5 gallons of gasoline before their oil was trashed.
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I think what you are seeing is the effects of "blow-by" in the engine. The rings are worn, and combustion gasses are being blown into the crankcase - contaminating the oil.
I have numerous small air-cooled engines, and they run a full season (used weekly) without much change in oil color.
One of my cars does have a similar issue. The oil does get dark rapidly, unlike the others. I attribute that to poor ring sealing when brand new. When I got the vehicle it had a few hundred miles on it, and even though I intentionally loaded the engine to seat the rings they did not seat well. I speculate that's from extended idling when delivered to the dealer. The day we first saw the vehicle it had been idling for some time, and I'm sure it wasn't the first time. Engines need load to seat the rings, and this engine did not get it until it was too late.