Low ash oil

We were discussing oil weights and such. A friend mentioned that IH went to low ash oil to alleviate a problem with burned valves in their gas engines. What is the main purpose or benefit of low ash oil and how would it affect the valves. Does anyone see a problem in using multi - weight oils in these engines aside from the detergent issues?

i am a firm believer in multi viscosity, detergent oils in everything.

There are a few places that multigrades shouldnt be used such as airplane engines, aircooled engine in hot weather, and old slowspeed engines.  The old slow speed engines should not use a detergent oil as they have a special sump for sludge to settle out in since they don't have oil filters.  Any engine that has been on a non detergent oil should have its pan dropped and cleaned of sludge before switching to a detergent oil as it cal break up the sludge and plug the pickup screen.  Detergents also neutralize acids. The is nothing wrong and is very much recommended to use high quality multigrade oils in water cooled oil filter equipped engines, preferably with oils that don't contain Pennsylvania crude base stocks.   Cant  go wrong with the oils by valvoline(napa/carquest), shell, mobile, and oils sold through major oems (agco, case, jd, cat, ect)

Ash provides lubrication to valves against the seats, but to much ash doesn't allow thermal contact between the valve and seat and causes over heated/torched valves.  Natural gas engines burn hotter than diesel so the need all the valve cooling they can get, where diesels have more impact(compression) on the valves so need a little more lubrication at the valves. Natural gas, depending on the source, can contain many impurities that can cause major damage to valves as well.    Modern high temp super alloys have reduced valve and valve seat problems so the ash content can be reduced significantly without the risk of valve seat and valve recession. 

As a side note, every one is going to low ash oil because of the impending EPA Tier four emission regulations.  Using an ash oil will cause the particulate filter to plug. 

In the IH gas engines use only the low ash oil.