I have used Delo 15W40 Multigrade in piston engine on my place from diesel tractor, lawn mower, diesel Benz's, Ford farm truck, Wifes 4Runner, yada - yada - yada, for about 12 or 13 years. I only recently began using anything else, and that is Mobil One in my new C Class, it just made since. The engines that I have taken apart which have run this oil were absolutely spic and span inside.
The added detergents in the universal grades work great in any engine. The only oil you will find that will do a better job of keeping an engine clean is Mobil One for about twice the price.
My advice; get that gas engine to operating temperature, pull the plug and filter, let it drain awhile, replace the filter, drain plug and pour that great Delo lubricatin' juice in the crankcase.
Have a great day,