If your Onan leaks coolant after it warms up check this out.
My Onan 8000 Quite Diesel generator started leaking coolant after the cooling system warmed up. At first it was minor and I thought it was just coming out of the overflow. Not so and it got worse. I replaced the radiator cap as required by the manual every two years but that did not solve the problem. At this point I knew it would be necessary to explore inside the generator and took the top off. I could see that the leak was coming from the bottom of the radiator near the lower hose but accessing that location was very difficult. I attempted to tighten the hose clamp but it seemed tight. Through not an easy task, I removed the radiator and the photo below shows what I found. Onan apparently used a hose clamp that would not close small enough to sufficiently seal the hose. I found two of these hose clamps, both on that hose. The other hose clamps would close further and I tightened them. There was one that was not accessible without a drastic dissemble of the generator. I have my fingers crossed on that one.
Bob, Pam, and Wheatens Buffy and Bo
2006 Diplomat 40PDQ
2007 Ford SportTrac
2006 Honda in standby