Just my 2cs, but when I looked at my own Mocal SP1T sandwich adaptor, I was aghast at the poor attention to detail in terms of the restriction of
oil flow within the internal passages in the thing. I spent some time with a die grinder, especially around the inlet/outlet ports, and around the internal opening made when the thermostat "opens". I would recommend a long hard look and think about this item, unless it has changed, and I did have a long talk with Mocal tech about it a couple of years ago, since I was so concerned about the restriction to
oil flow it represented.
The thermostat on mine does work as advertised (can feel no temp at all in the
oil lines or cooler until the oil is right up to temperature). You could try a replacement "waxstat" - accessible when you unscrew the black hex headed plug on the side of the thing, and available from Mocal as I understand. Could be yours is "tired"??
And I used dash 12 lines to and from the oil cooler/accusump. Jolly expensive, all those -12 fittings, and as for the -12 non-return flapvalve!
HTH