Not a joke at all. Right now I have a mixture of 3 oils in my car; 0W20+5W20+5W30. I honestly did that because it was oil I was going to throw away, but I decided why waste oil that I can just run through my car for like 6,000 miles to "rinse" my engine. Then I realized it seems it dropped my MPG. Since I like to hypermile, I usually get around 60mpg, but I am seeing only around low 50s. So, I was wondering if this mixture of oil is thick and has dropped my MPG. Hence the reason why now I wish to dump the oil sooner. Say sometime between 2,000 to 3,000 miles of use.I hope you are posting this in jest. I doubt that it will it will cause major engine damage………..right away. But it will cause engine damage down the road. Who knows, maybe 20k, maybe 40k…………. But it will. Engines, especially modern engines are designed and set up for specific types or weights of oil. It is not just the inside of the engine block but many other variable parts rely on it. For fun I asked several of my mechanic friends, both on line and in person and everyone was amazed. Not in a good way. Everyone laughed their a$# off over it. Not in a good way. Honestly, and I do not mean any offense, I just want to make my point, only a completely ignorant person would do what you have said you did.
When I drain that oil, I am still pondering on the idea of using 2 quarts of Toyota 0W16 mixed with 2 quarts of Castrol High Mileage 0W20. It is not yet set in stone that I will do that, but I am positive I will try it out and see. That is why I went ahead and bought the Toyota 0W16 oil. If I do put this mixture of 0W16/0W20 oil in my car and at some point I feel uncomfortable about it, I will drain it and put 4 quarts of 0W20 back. I am genuinely wondering if it will have a negative impact. I am still looking into that, though I am willing to give this a shot and see.
If I do end up putting this 0W16/0W20 mixture in my car, I will use it for atleast 5,000 miles or more and send a sample to Blackstone for a Used Oil Analysis whenever I change it. It would be interesting to see what the analysis will say.