Field note: chasing an overheating Waukesha VHP
It wasn't the radiator. It wasn't the water pump. It was the AFR table — six years out of spec.
By Megawatt Maintenance
We took a call on a Waukesha VHP L7042GSI that had been creeping hot for months. The customer had already swapped the thermostat and the water pump — twice. The temps kept climbing under load.
When we got on-site, the obvious things checked out. Coolant flow was fine. The radiator was clean. Charge air cooler was within spec. The engine ran cool at idle and turned ugly above 80% load.
What we found, eventually, was that the AFR table on the ESM had been hand-tuned by someone six years earlier and never revisited. The engine was running lean enough that combustion temps were elevated — exactly the kind of issue that wouldn't show on a quick visual but would compound under continuous duty.
We reset to factory baseline, ran a controlled re-tune, and verified with EGT probes across all cylinders. Temps dropped 14°F under full load. The engine has been steady for six months since.
Lesson: when the mechanical side checks out, look at the tune. Especially on engines that have changed hands or service vendors.