thermostat

[ca3k]

Hi all new here and will appreciate any and all assistance here.
For the last week or so when my 97 cutlass supreme sl is stopped at a light or parked and idling i get a faint noise in the cabin. Almost sounds like its consistent with the idle but then seems more random at times. The car seems to be running a little cooler than normal(right around 1st white line) but occasionally gets within the normal zone(in between both white lines). it also seems to not have the noise when its at the normal temp zone. usually you can barely hear the noise but at times gets a little louder. the gf says she can feel it in the floor with her feet.

My thoughts are to change thermostat and flush coolant because ive read running cooler means thermostat is stuck open. I thought of cleaning out the heater core if possible, i cant locate the heater lines.
My heat seems to blow pretty warm not hot but def not cool, it is about 75 degrees here i would expect at least warm air to blow. And i actually seem to be getting better fuel mileage the last few weeks 24+ city. This seems inconsistent with what ive researched about stuck open thermostat symptoms

thanks in advance for any adivice

[Schurkey]

For the last week or so when my 97 cutlass supreme sl is stopped at a light or parked and idling i get a faint noise in the cabin. Almost sounds like its consistent with the idle but then seems more random at times. The car seems to be running a little cooler than normal(right around 1st white line) but occasionally gets within the normal zone(in between both white lines). it also seems to not have the noise when its at the normal temp zone. usually you can barely hear the noise but at times gets a little louder. the gf says she can feel it in the floor with her feet.

I can't help you with the noise.

My thoughts are to change thermostat and flush coolant because ive read running cooler means thermostat is stuck open. I thought of cleaning out the heater core if possible, i cant locate the heater lines.
My heat seems to blow pretty warm not hot but def not cool, it is about 75 degrees here i would expect at least warm air to blow. And i actually seem to be getting better fuel mileage the last few weeks 24+ city. This seems inconsistent with what ive researched about stuck open thermostat symptoms

Good plan. Yes, thermostat is probably stuck open. I've dealt with that on other vehicles including one Lumina. Your symptoms are logical for a stuck-open thermostat other than the improved fuel economy and the "noise".

Don't forget to open the block drain plug(s) to remove the flush-water (and settled rust/contamination), otherwise you'll likely have too much water and not enough anti-freeze when you finish.