The oil thermostat is built into the base of the oil filter cannister and the lines to the oil-to-air radiator leave at that point. When the oil gets up to about 100C, the thermostat opens and oil flows to the radiator. Until then, the oil flows directly to the engine.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970