OM 651 Oil in Coolant

Hello,

I recently acquired a 14 E250 with 122k miles.

I noticed one morning that I had a check coolant light on the dash when I started the car. I went under the hood and noticed that the coolant which was once pink now turned black.

Doing some research, I replaced the oil cooler and flushed the system a handful of times, yet it still has oil in the system.

I performed a combustion / block leak test with a co2 fluid (the correct red one for diesel) and it showed negative.

I used a...

OM 651 Oil in Coolant