I ordered a closed cooling system for my VP 8.1Gi... (block only) and I'm wondering if there are any specific procedures or special coolant needed for this ? or if I can just run down to my local Autozone to grab a few gallons of off the shelf antifreeze ?

Not sure how much water still lays in the bottom of the block. The engine sits pretty low in the hull so there is no way my old a$$ is reaching the block drain plugs down near the pan rail.

Can I just mix/flush system a few times ?

Talk to me...

Problem with that is the water in your engine now is full of minerals and etc. Most prefer to mix antifreeze with distilled for better protection.

That said a bbc block holds about 2 gallons. Add more for Hoses and coolers and etc.

The 8.1, being a marinized GM 8.1, was intended to be used with Dex-Cool, but it really doesn't matter, so long as you don't mix incompatible types of antifreeze. Go green, or go orange, but don't mix them.

I converted my 8.1Gxi to fresh water cooling using the VP kit. I initially went with the Dexcool after flushing and draining the block completely. However, I found that the Dexcool for whatever reason kept silting/claying up which it will do when it goes bad. So, I flushed/drained everything again and went with good old green stuff. No problems after that, but it doesn't have the service life of the Dexcool.

Installing the kit isn't a cake walk and you are going to be knee deep in the bilge anyway, so I would plan on getting those drain plugs out to flush and drain the block really well. Especially if you have salt water hours on it.

Boat has never seen salt and has spent its entire 416 hours on LOTO water.

I've had similar crud issues with dexcool. Never had any trouble with the good old fashioned green antifreeze. I'll grab 4 gallons of the green stuff. That should be enough to flush and fill the system.

No idea how long until the kit arrives. Ordered it from Hardin and the disclaimer basically says its a drop-ship item.

Maybe it will be easier if I lift the rear seat/hatch off the engine compartment. The heat exchanger tank mounts to the rear of the engine and thats the hardest area to access with the limited stroke of the lift cylinder.

If you are possibly modifying this motor or pulling it out altogether, why are you installing the closed cooling kit?

Its a quick easy upgrade that can be carried over to the next engine if/when that happens.
I was just looking at Dart 4.5" blocks and 4.5" cranks today.
I think a mild 572 will be the direction I go with it... but it may take until next year to get everything together.
This has to be a slow roll to fly under wifes radar.

Volvo DPX has left the chat.

I would flush the system with fresh water from your hose.

Drain it all, when you pull the old hoses etc...and pull the block drain plugs.

Use distilled water and the anti-freeze coolant that is recommended for your application.

I prefer concentrated vs the pre-mixed. Pick up a hydrometer ($10) to measure coolant specific gravity.

This all depends on how old the block is. You prob don't want engine block coolant passage oxidation pieces plugging up the heat exchanger tubes.

I'm looking at converting a 370 TRS BBC to fresh water. This engine never sat for long periods of time in salt water moored etc.

Salt can attach to metal when it reaches higher temps.