oil thickness in stock engines

Why does all the non-mechanics I meet say to use the super thick stuff? Last time I had 10w40 in my engine, it made noise, ran clumpy, and when changed out, was sludge like in texture and really dark. I used to change oil at a reputable location in town, and every vehicle with the thicker "junk" in it ran like a retarded kid on crack, the oil came out like tar, and sometimes didn't all come out unless engine was running at warm temperature. I personally wouldn't even put 10w40 in my lawnmower because of this. Actual mechanics I have met said to only use the thicker stuff if you use performance addons, drive in extremely hot climates, or run at high rpm's alot. I don't know about the thicker stuff .. your take? Stock engines now, no mods. Now when I run recommended thickness, 3000 miles later, it comes back out looking almost new, with only a mere slight color change, like it's a new engine again, and runs better with more power.

IMO, that's the reason they AREN'T mechanics. Guaranteed there's people on this website who know more than some certified mechanics.

theres a reason honda engineers recommend 5w-30....

So what if the dealer puts 5w-20 in a 98 ex I4. They tell me it has 5w-30 in it but all my doc says they put in 5w-20. should i make them change it or just roll with it for the next 3000?

its fine