I ran distilled water only in mine when I changed over. I changed it about 4 times before putting dexcool in. 502 mag mpi . It’s now a carbed 540 and still using the same system.

I seem to recall I did something similar.

Drained block, filled with distilled water with no thermostat, ran it and drained it again. Repeated that exercise a couple times. Then filled with 50/50 AF/Distilled water. I used the green stuff because that's what CP Performance told my to use and it was their kit.

Mine are 800hp 565's - greatest money I ever spent on a boat going to Closed cooling. Temps are unbelievably consistent and never climb over 150*

I did on my VP 8.1GXI because it just never ran right with the raw water cooling. The consistent temps went a long way to sorting out its usability issues. In the end, the stock Volvo tune was just not very good on that motor.

Closed cooling on fresh water lake. Running a 160 stat compared to a 180 stat. Any advantage bumping to a 180? Eng. 406 cubes Dart Block.

Ive run mine a few times on regular chlorinated city tap water and it seems to stay pretty clean.
I fill a 110gal tub with water and lower the drive into it. Works better than any muffs ive used and doesnt overpressure anything. My tap water is probably 75psi.

Really looking forward to closed cooling and actual antifreeze in the engine.
Estimated ship date on the system is 10/31... so now we wait.

I assume this blue fitting is to flush the current system ? (never had anything VP before)

This is probably the most frustrating part of my VP ownership... the lack of aftermarket support and tuning options. Mine has what I believe is "California emissions tuning" which I'm sure makes it run sub-par and lean.
Maybe I will bump the fuel pressure up a few PSI. It's about the only thing I can tamper with. (the regulator is adjustable.)

My Merc 496 MAG had the same sticker on it.