that's air in your cooling system,,,, and your hearing it in your heater core

 

You need to park your truck on an incline (front pointing up), open up the rad cap and let it run for about 10 to 20 minutes. You need to give it enough time so it can get up to temp so the stat can open and release any trapped air. Then just top off and your good to go. You'll know you bled all the air out when you no longer hear that rush off water sound.

 

mine used to sit around 195ish. but since a new radiator and thermostat it hangs right in the middle between the 210 mark and the first mark above 130. maybe thats why i get 12-13mpg now a days and i used to get 13-14.

 

Weird, I went with a 165 or something and I run at about 180, I used to be at 210 or so, but I too noticed it getting a bit less in the fuel milage. But I get about 18 from my 360.

 

18 from a 360? i think you're listening to the lie o meter instead of the odometer and a calculator.

 

My temp gauge is recently reading exactly between 130 (not the mark above it) and 210 and I've noticed a loss in mileage. Would you go ahead and replace the thermo with a 180 or 195 unit?

 

i used to be around 200 put in new t stat and id say around 180-190 its amazing my heat gets warmer faster and the truck seems to be healthier

 

My truck was running 20-30 deg high and found the problem was the gage.
After changing the thermostat, fan clutch & water pump, took the truck to a radiator shop. After measuring the thermostat housing and radiator inlet to be 200 deg, F and the radiator outlet at about 180 deg, F with an infrared temp gun, they assured me it was fine.
Purchased a Scan Gage, which connects to the obdii connector, and receives its info. from the PCM. It too displayed 200 deg. F.
A '96 FSM shows two water temperature sensors. The PCM receives an input from a sensor on the drivers side adjacent to the thermostat housing. The analog dash board gage sensor is located on the passenger side under the alternator.
The FSM, under a section called Temperature Gauge Calibration, shows low normal 362 ohms at deg. F and 77 ohms at high normal. In order to make the dash gage and scan gage agree at 200 deg. F, I had to add 30 ohms in series between the analog sensor and the dash gage.
(Found an infrared temp gun at Harbor Freight for about $35. Pretty handy device.)

 

you can get an infrared temp gun at advance for 20$

 

That's weird. You would think a new rad would help it stay at a certain temp, if not cooler.