Recently we have come across a few issues with the Yanmar 4TNV98 diesel engines, we have had them externally crack tested and machined where required and new gaskets fitted genuine parts, torques to recommend settings and re torqued, with-in a 1000 hrs again we find they are bubbling in the radiator again causing overheating.... we have replaced water pumps on most of them as standard procedure but still having issues with over heating and gaskets failing.. anyone else having/had issues? Very much appreciated thanx