This 80 has an auxiliary fuel tank, but I have not used it yet. Does anyone have recommendations for what would be smart to do or check before using the tank?
If you haven't already, maybe check the fuel isn't dirty.
Otherwise, hit the sub tank button and use up the fuel that's in it.
The hdj80 subtank system has two 3way solenoid valves that switch pickup and return line from main tank to subtank.
When you draw fuel from the sub tank, the spill/return line goes back to the sub tank too. This is because the diesel injection pump relies on recirculating unused fuel back to the tank to lubricate and cool the injection pump.
I used to run the main tank until close to empty, then use the subtank. Refill both together.
This keeps fresh fuel in the sub tank so you don't have to worry about algae growing in the tank.
My diesel cruisers were always daily drivers, so the fuel was being refreshed regularly.