Onan Coolant Leak
I have been pulling my hair out trying to find a coolant leak in my 8kw Onan genset. Recently, I pulled the heat exchanger and had it cleaned out at the local radiator shop. Replace a bunch of hoses at re-install, ran it for hours and all was good. Put sound shield back on and proceeded to use as normal for the remainder of the season. On our last trip, I opened it up to check oil and noticed some coolant in the bottom tray. I mopped it up and added some more, fired it up and checked for any obvious leaks, found none. I chalked it up to maybe I filled it too much and the coolant was from expansion. Left it and all was dry. 2 weeks later, was down at the boat and decided it was time to change the impeller, opened the sound shield and there was at least a quart or more of coolant in the tray. So, it's leaking from somewhere while not running. Checked all the hoses, connections, water pump, etc. and nothing.
I'm thinking that I need to pressurize the closed side of the system and check for leaks, just like a radiator in a car. Any suggestions, comments, advice?