430 starting issue

OK all you wonderful diesel guys. I need your help. Was using my 89 430 mowing. mowed 2 hours, drove it 6 blocks to fill with fuel. Started it up left for home. Saw a friend working on a 46 truck, stopped to chat. went to start the tractor nothing. It was kicking in the fuel solenoid but would not engage starter. pulled home 6 blocks and left it in the barn for 4 hours. went in and tried it and it started. Seems it won't start when warm. what the hey. any thoughts. thanks Doug