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Have you considered heat exchanger?

I got rid of Setrab oil cooler on our track E30 and replaced it with water/oil heat exchanger. Bliss. No more oil thermostat, water thermostat takes care of everything. Oil is heated up quicker whole installation is easier as we do not need oil hoses going over radiator. Visco fan is removed too, so car relies on air moving. Radiator upgraded to "tropic".