The stat on my V6 was stuck open.
The heater only got warm, not hot. The temp gauge didn't get to 70.
With a new stat, the heater gets hot and the gauge is at 85 on a run and the fan kicks in just over 90.
What does your gauge get to?
Also, have you changed the pollen filter since you've had it? It's under the scuttle panel on the passenger side. My 'properly serviced all its life' cars filter was choked and that was restricting air flow into the car.
I got half a bag of 'compost' off of the bulkhead at the same time