What year is your car? On our 1994 940, the resistance of the temperature gauge sender is about 2500ohms with a cold engine, and about 200ohms fully warmed up.

If your new sender really is showing 4 ohms at room temperature I would think it is faulty. Did you mean 4k ohms?

BTW, these gauges have some kind of compensating circuitry in them to dampen out needle movement once the engine is warmed up - ie: minor temperature fluctuations do not move the needle. I observed the sender resistance varying considerably when comparing normal speed to idling in traffic with my multimeter connected to the sender terminals, but duplicating the driving conditions later, the gauge needle never moved from the 12:00 spot.
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Bob: son's 81-GL, dtr's '94-940, my 83-DL, 89-745(V8) and 98-S90. Also 77-MGB and some old motorcycles.