[Barry Rooker]

3-4 years ago, back when my engine ran a steady 180, winter & summer, the temp gauge hit maybe 200 on a long grade or at 105 degrees in the desert, the temp gauge needle would plummet, like a rock, when the fan went to 100%.

It was, literally, like flipping a switch. I'm not seeing that lately, suggesting that something has changed in that department.

I've got more research to do: DDEC reader & temp's shown; more infra red gun comparisons with the temp gauge.

My engine coolant thermostats are new & are marked as 180 degree units. The housing was crud-free, no coating seen. That was encouraging. From what you're reading in the Detroit 60 manual, apparently, they open gradually. Hmmm...several variables here.

Newell sounds somewhat baffled when I speak to them about DDEC fan on/fan off temps & the possibility of re-setting them at the DDEC. I'm thinking Detroit shipped these engines with pre-set on/off temps in the DDEC, possibly specified by Newell or chosen by Detroit. But that doesn't explain the apparent change in my hydraulic fan's on/off temp. I'm in way over my head.