If you are running a diesel, and you are on a diesel forum so I'll assume that is the case, you should already be using a 40 weight oil. The number that matters once the engine is warm is the last number. If your blow by is excessive with 40 weight oil, the next step is a 50 weight oil. It can be hard to find diesel ratings on say a 20W50, but there are some out there. Mobil 1 has a 15W50 with a diesel rating. The Motor Honey approach will work, but you have no idea what your oil viscosity is after adding a bottle, so I would try the higher viscosity formulations first.

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