Hey thanks like always "142Guy" you always have the good info I am looking for. If you ever get to NY make sure you look me up so I can buy you a drink77 deg C (170 F) is the coolest thermostat that I have ever seen for a Volvo B18 - 20 and I think that you would have to order it from a European vendor. 82 C (180 F) seems to be the go-to thermostat. If someone is offering up a 160 F thermostat, I would be highly suspect that it is a Volvo specific thermostat. It might fit the thermostat housing; but, may lack the little flap thing on the bottom which closes off the internal by-pass circuit in the block. Without that by-pass close off you will have over heating problems.
The back of the head on the B20E where the temp gauge sensor is located does run hotter than the front of the head where the thermostat and the D jet sensor is located. After protracted idling on a hot day the back gauge on my B20E can be reading up to 15 C higher than the front temperature measurement which is always 82 +/1 Deg C after warm up. This temperature skew rather quickly disappears when the engine is running faster (car moving or just speed the engine up to about 2000 - 2500 RPM). Cruising at 50 kph the front and rear temperature measurements are within 1 or 2 degrees of one another. If you are boiling over or filling your expansion tank right to the top with an 82 C thermostat, I suggest that the radiator and the block may benefit for a trip to a good rad shop that can do a clean out using the very nasty chemicals that are available to them.
I don't know what the warm-up enrichment curve is for the D jet, but, I expect that by 77 C it should be well out of any warm up enrichment.