My '83 W250 was a ranch truck for years and it shows here and there. I had a valve cover gasket leak on passenger side and those old gaskets appeared to OEM, hard and brittle! Pulled the valve covers and decided to soak them in diesel first to remove some sludge and was looking at the valve train which is fairly dirty with some buildup. If I took a spray unit and washed down valve train with diesel, would it simply drain into sump directly from cylinder head? I would then immediately drain sump, (NOT run engine) refill using Rotella ( pretty strong detergents in this oil), new filter and drive truck for a thousand miles, drain and then perform a regular oil service with Rotella again and next time change around 3-5,000 miles depending. Bobistheoilguy is a pretty good site, might weigh in with those folks. There other thought is drain a quart of oil, add quart of diesel and let idle for 15 minutes and then drain as a place to start. Any thoughts on this madness?

 

The consensus at that oil site I mentioned is a rapid change in oil change interval cycle with a good detergent oil and let time do the rest (gentle approach).

 

Yeah, just use a good detergent oil, and change it more often for a while. You don't wanna break all that stuff loose at once.....

 

If there is a lot of sludge don't be surprised if the oil pressure drops. It can get caught by the pick up screen and starve the pump of oil. Another option is run it with diesel/kerosene etc for a short period then let it drain into the pan. Drain oil and remove the pan. Then thoroughly clean everything. This means you can use a spray bottle filled with cleaner of your choice(diesel/kero) with a brush to clean the stuff that didn't come off. Let it drain out the bottom of the motor into a pan(not the one that goes on the motor). Reinstall the pan with fresh oil.

 

Do any scraping of the top end with a shop vac in hand and avoid stuff falling into the pan

Plug what you can with rags and go at it. Remember a strong detergent oil can turn a weeper into a leaker.

If the top end is really nasty you should give consideration to dropping the pan.