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I’m trying to sort out the cabin/bay/domestic water heater engine coolant loops. It appears there are two loops: one to the heat exchanger in the water heater and one that runs through two water-to-air exchangers in the bay and on through an exchanger under the bed then up to the dash heat. I find four valves on the engine. Can someone tell me which are send or return valves? I’m thinking the two upper are send. Looking for affirmation or more knowledge about this system. Thx.

So generally the upper valves are the supply and the lower ones are the return as you said. It’s hard to see exactly where the valves are in your pictures.