You could use either Seafoam, or a home brewed seafoam alternative in your crank case to clean it out.
How to use SeaFoam to clean your Engine – The RIGHT way!
OK, you’ve got another can of Seafoam, right? Good. This can is going to be used to clean oil rings and lifters, clean built-up oil residues and contamination from the crank case, and clean the PCV system. You’re going to use 1.5 oz per quart of oil. Check your owners manual (or, again, ask on the forum). If you have a 5-qt oil capacity, you’ll be using 7.5 oz of Seafoam (roughly half a can). While the company claims you can leave the Seafoam treatment in your crankcase until your next oil change, I’ve found that most engines with higher miles have a LOT of nasty buildup, which can really take a toll on your oil filter. Therefore, I like to do an oil change roughly 50 – 100 miles after adding Seafoam.
The other half of the can? Add it to the crankcase after you change the oil if you had a lot of sludgy buildup, OR dump it in your fuel tank at your next fill-up. Seafoam is safe to leave in the crankcase with clean oil until your next oil change, and it’s also a great product to clean your injectors and fuel system. In fact, it’s even credited with helping remove some of the deposits that cause a faulty fuel gauge reading in some cars!