I had the same code showing generator overheat just two weeks ago. I was charging batteries (see my other posts about why I was doing that!). Went to bed and woke up as the bilge pump kept cycling on every couple minutes. Turned out the Sea Dog strainer was leaking around the seal under the clear plastic twist-off cover. Shutting off the raw water sea cock let me get back to sleep that night. I'm sure glad I was on the boat when it happened. It is likely that the reduced water inflow (due to the leak) is why the generator overheated.
Well, the sea strainer costs about $10 on Amazon so I ordered the same # part (#364136 5/8" strainer) that I pulled off the boat.
The correct model came but it has tubes on the size way bigger than the one in the R15. It seems to have a 5/8" inside diameter, while the old strainer that came on the boat was about 5/8" outside. You can almost shove the old strainer's input/output tube right into the tube on the new one from Amazon. The new one has a fine mesh screen (see the picture above) whereas the old one from the boat has a nice coarse screen. The fine screen is sure to clog quickly from normal goop sucked up. I checked and both have the same part number. I figured something was wrong at the factor so I ordered the next smaller SeaDog, but that one came with a fine mesh screen and too small tubes to be of use, it is #364135 with 50 mesh for 1/2" hose. To make matters worse, if you pull out the O-ring to try to match it so as to buy spares, you won't be able to get it back into its seat. It's too big!
Ach! I sure don't want to work in that engine compartment trying to force the hose from the sea cock and the generator onto the larger tubes attached to the replacement SeaDog strainer, nor do I want that fine mesh. I'll see if I can reuse the old one and maybe just stick a new clear dome from one of the new ones I bought on it to stop the leaking. Beware, keep your old parts as you may have to reuse them. NOTHING IS EASY!
PS. For those of you having difficulty twisting off the plastic tops of these things, filters, etc. Keep a set of these on board, they work great:
$15 at Amazon and cheaper elsewhere, even a Walmart.