Vexing Perkins 4.108 cooling issue

[keelbolt]

So during my spring commissioning I thought it best to flush the cooling system as the coolant was starting to look more like cappacino than lime aid. This is easily accomplished on my vessel as there are two convienint flushing/filling ports in the piping that goes up to my domestic hot water tank which is mounted about 2 feet aft of the engine and elevated above it by about 1 ft. Last time I flushed and re-filled, the engine began to overheat on the first run. I simply cracked one of those handy valves with a bucket under it until all the air was out. Temp came back into the normal range and has been fine ever since. That was ~5 years ago.

This time around, I cant seem to get any pressure to build out of the coolant pump. I started with cracking the valve, like last time, and nothing came out. I pulled the t-stat and tested it in hot water, and its fine. I pulled off the coolant pump and it looks like the day it was made. Spins freely by hand with the belt off. I'm thinking there's still a vapor lock somehere, but if I blow into one of those handy vavles, I get pure coolant out of the other one.

There is a bleed valve at the lower right (as I face the engine) that is used to drain the system, if i open that a little dribble comes out until I open either the Hx filler cap, or either of the handy vavles, so I htink the system is sealed up tight and not sucking air anywhere.

Any clues? I've spent the better part of two days scratching my head on this one...

Thanks in advance.

[rbk]

Does your engine have the bowman heat exchanger or marine version (heat exchanger at the rear). Either way make sure the HX is bled as well.

[keelbolt]

It is a Bowman Hx

[rbk]

Maybe the Hx is fouled? Sucked up some weeds? Calcified? I’d pull the core and see what’s going on in there. I’ve never had issues with air locking on mine so I would be looking at the Hx or the raw water intake/impeller, maybe missing a fin or two?

[keelbolt]

I finally figured it out. The suction hose from the hx to the block was air bound. Not sure why its never happened before, but it was an easy fix!