TxGoat wrote:
You can add MMO to crankcase oil at up to 20% and leave it until the oil needs changed. One quart in 5 is plenty. The same is true for Rislone.

I would not add harsh, volatile solvent, like B-12 Chemtool, to the crankcase oil.

I would not add diesel fuel or kerosene to the crankcase, either.

If your engine has an oil filter, I'd replace it.