my fc is reading very low it's around 108 F my temp sensor is placed below the thermostat on front of the water pump housing. i tested the sensor to see if it was bad and it checked out ok. is this a sign of a stuck thermostat?

 

No,a stuck- or even absent- thermostat couldn't keep the water temp that low.
There's a problem with the sensor or it's placement.

 

it might not be exposed enough to the flow i'll go and check that.

 

That would make it slow response. Yours seems to have an error indicated temp vs. actual temp.

Are you sure that the sender belongs with that gauge? The sender might be working correctly but a mismatch with the gauge would make the gauge read incorrectly.

Good Luck.

 

The most likely cause would be either a seized thermostat in a "fail-open" mode, or a missing thermostat all-together. Are you getting any heat from your vents? If not... then you probably need a new thermostat.

 

"Most likely cause" in your dimension maybe...in this world, no.
No running IC engine- Wankel or piston- has a coolant temp of 108°, whether the thermostat is stuck open or sitting in the passenger seat.
You take showers in hotter water than that.

 

A stuck thermostat would yield a low temp... for a while. But eventually the temp would come up to full. My old set up (previous owner + build) had the haltech temp sensor drilled and tapped haphazardly blocking the t'stat. My car would take about 20 minutes of driving before seeing the water temp gauge reading normal. How long is the car running when you are taking the reading? If it's after than an hour, then we can definitely say it's the sensor.

 

it wasn't long i drove it around for about a hour the other day and the temp went up to 130 ish i tested the sensor in a pot of boiling water but when i took the pot off the stove and walked out side it cooled down and my sensor read only 193 so i'm sure it is working right i just don think the sensor is far enough into the coolant i checked and about 1mm of the sensor was only in the flow.

 

Seems like too much of the sensor bulb is shrouded and the surrounding metal is acting as a heatsink, resulting in an artificially low reading.

 

But the surrounding metal should also achieve a temp equal to that of the coolant. Perhaps the guage itself is screwed? Or possibly isn't grounded well?

 

Are you sure where you drilled the hole for the sensor, that the sensor is now reading the output of the radiator going into the water pump instead of reading the output of the water pump going to the radiator?

Once upon a time..........I installed a sensor in the passage where the drain plug for the *block* is. It read low temperatures/false readings. Because that passage is a dead end passage and ther is no water flow in that particular passage. Just FYI. Not much to do with what your doing.

 

isn't the coolant sensor for the guage on the rear housing( i know s4 is), the sensor on the waterpump housing is the coolant sensor for the ecu

 

The stock sending unit is located there but I think the OP has an aftermarket unit installed.