5.56 wrote:idk where this myth came from: "switching oils will cause damage". its pure garbage. you can pour half a cup of every single motor oil on the market (as long as they are slightly similar weights) - NOTHING WILL HAPPEN.
you can switch back & forth between synth, organic, mix. heck you can even mix 2 bottle of 5w-30 syth and 10w-30 organic and NOTHING will happen to your motor.
funny story: i was in walmart the other day, specifically the engine oil isle all the way in the rear, and some guy was "educating" his girlfriend on engine oils. he said "you dont need synthetic. because once you switch, you can never go back; its cause all kinda of sludge and ruin your motor. so since synthetic is super expensive. so just stick to the normal oil."
-if she was hot enough, i would have stolen her form him right then and there lol. but lucky for that fool, she was kinda busted LMFAO
Having previously worked in the motor oil industry, I can tell you the myth around switching oils dates back quite a ways. It originates from a time where there were some early synthetics with high concentrations of detergents and some cheap oils had very little to no detergents. This would lead to deposits of fairly low-density sludge building up in an engine. When someone switched to a motor oil with a high detergent content, it would potentially break a chunk of the sludge loose and clog an oil passage...
However, that was a long time ago. Now all motor oils contain detergents and moderated levels of them, so that deposits dissolve slowly. Sometimes adding in a bottle "oil treatment" to your oil, however, can cause this problem. With industry standards like ILSAC GF-5 (or the upcoming GF-6), motor oils are typically more similar than they are different and there is relatively little disparity in performance parameters.
http://www.gf-5.com/
Regarding "high-mileage", not all high mileage oils are created equal. Some just have slightly higher levels of detergents and are mostly marketing. Others also have product-specific or elevated levels of anti-wear additives, seal conditioners, friction modifiers, etc. It is best to do your homework.