Its certainly possible if the engine is dirty and you put Redline in with Esters that do more cleaning. Obviously if you don't dompletely drain you would see it. Its a valid question but I don't think its a real big deal. I think you will at least see a trend-up or down. But should be able to sort it out somewhat. Certainly Terry could. It makes sense though for the sake of confirmation and better trends to get several samples of the same oil at different seasons/driving conditions. Again-very valid question.