Small Engines (Lawn Mowers, etc.): JohnDeere GX345 with bent push rods, grass clippings, push rods

Question
Good evening Mr. Bridges.  You are highly respected on this forum.  Keep up the great work!
I have a 2005 JD GX345 with 360 hrs. Serial #MDG3458114794
water cooled Hydro 54" with a Kawasaki V-twin.  I mow 4 acres.  I took a break while mowing the other day and when I tried to restart, it wouldn't.  Check everything I knew to check and gave up to take to shop where I bought it new.  Just out of warranty.  They serviece it every spring for me.  The had to disassemble the engine  to diagnose.  They found bent push rods and had to do the following:
Replace push rods, valves, gaskets and seals and have the head shaved. Drained and flushed radiator.  All totaled $700.  I check all fluid levels between mowings.  I did have the temp overheat light come on just for a second earlier in the season.  I imeadiately stopped and cleared grass clippings from around the front grill screen and radiator.  It ran fine up till I tried to restart after mowing about 2 hrs the other day.  What are some reasons that the push rods could have bent?  Is this unit running hot even though it's water cooled?  I use cool guard from JD in the radiator.  Any ideas on what could have gone wrong?  ....John Deere was nice enought to reduce the cost by 25% since it was just out of warranty.....

Thanks!

Jeff

Answer
Hello Jeff:

Paul the Truth Miester is the JD Expert here and I Answer the Questions if I Know a Reason for the Problem. Paul Works on the JD Equipment Everyday and has More Experience with JD Products. However, I have Found that Under Certain Conditions, the Water Cooled Engines Do Tend to Run Hotter than Expected. This will Cause the Valves to Stick and Bend. If the Humidity is High and the Temperature is Also High the Engine will Run Hotter than a Hot Day with Low Humidity. This is More of a Specialized Question that Would be Seen by a JD Mechanic more than I. The Few Times I have Seen this, the cause was a Restricted Cooling System. Did they Flush the Engine when they Flushed the Radiator? Some Flush Only the radiator. Is the Thermostat New? The Engine Cooling Ports can become Restricted and Cause the Valve Bending Problem. Usually Flushing the Radiator and Engine Corrects the Problem. Hope this Helps. I am Here if You Require More Assistance. Let me Know What Happens, Please. Thanks.

Good Luck

Respectfully

John