Any tips for finding a coolant leak and or recommendations for a dye? Does the coolant need to be replaced after this dye is added? Took off the undershields to add a famoto oil pan valve and see what looks to be dried up coolant staining on the subframe and the felt material of the undershield. Will post pictures soon.

 

Check the coolant lines going into the turbo. Both are susceptible to leaking. Very common on P400s, less common (but still possible) on P300s.

I had a faint smell of coolant for years on my P300 Defender. Finally decided to poke around as my warranty was running out and found the same staining on the under shield and felt. Traced it to the lines going into the bottom of my turbo. (not sure if the lines are also at the bottom or the side of the turbo on P400 engines, but you'll see it if that's the issue for sure).