Well a little update. Since most posts didn't indicate it to be a common problem and the radiator needed repaired anyway ( wouldn't hold pressure is an understatement, both the front and rear seam on the upper tank blew and the tank bulged outward) I removed it and inspected it as I repaired it. Although the guard in front of the radiator was clean, the fins in the radiator were easily 2/3 or more full of mud/fine grass and who knows what else. It took easily 30 minutes to completely clear them. After clearing the fins, and straightening a few, I repaired the tank and re-soldered it and pressure tested it..held fine. I now believe what happened was that the radiator couldn't dissipate enough heat while I was mowing for the extended period and the coolant got hotter and hotter, eventually turning to steam. The steam was releasing into the recovery tank with such force it kept blowing the top loose. After a certain point the steam couldn't release fast enough through the overflow tube as the heat built up and created enough pressure to blow the seams apart. It's repaired now and the paint is drying, I'll install it tomorrow and give it a test, but am pretty sure that was the problem. I'll post tomorrow with the results. Thanks for all the input, I was afraid that head gasket failure was a common issue...much like some of the V6 Ford engines.
Now.. what about the front wheels??
Now.. what about the front wheels??
