i have a 2000 4x4 2 door 4.3L chevrolet blazer, i've searched the forum for this problem but nothing seems too quite match this issue. so one day i had a cracke in the radiator's top tank and i replaced the radiator and a 195 degree thermostat and thats when my problem started, i noticed my fuel mileage was lower then usual so i started troubleshooting and found that my coolant temp. was a little low and was not reaching the full 195 temp. it's only reaching about 180 degrees(verified with my scanner and temp gauge and temp gun) so i replaced the thermostat again with another195 degree aftermarket stat and still only 180 degrees, so i go to the dealership and buy a factory 195 degree thermostat and STILL 180 DEGREES....W T F ???....so i also noticed my clutch fan kinda cutting in and out slightly, almost variating while idling so i also replaced the clutch fan which was bad, but it was not my problem which i figured as much but i figured might as well since i'm under the hood. so if the thermostat is supposed to be 195 degree then why after 3 different thermostats it still only reach 180 degrees? i've bled the system every time i opened it up at the bleed screw at the thermostat housing so i dont think there is any air in the system, so....... 3 bad thermostats in a row?

 

My thought would be that there is still air in the system. It is highly unlikely that you received 3 bad t-stats in a row and the t-stat is responsible for controlling the temperature of the coolant in the motor.

Just a quick question though, you are putting the t-stat in with the bulb down right?

 

could the tempature sending unit that communicates with the computer be bad? i seen them go bad where they wouldnt even register. had one during a summer day tell the computer it was running at 22 degrees so the engine was running really rich.

 

i installed all thermostats spring side down.

To ABIG84 i checked the coolant temperature with a temp. gun at the metal tube right at the thermostat and it reads 180 degrees just like the temp. gauge in the instrument cluster and my scanner reads, all readings are the same temp. so i know that the coolant sending sensor and the ect sensor are both correct.

 

I can't remember how many years back I replace my radation for the side plastict cracked. While I had the radiator off and coolant drained I went ahead and put in a new thermostat, ever since that day my temps has not run as high as before. From the time I got it till this change it would run right up close to 200, constantly, since them its ran just over 180.

Sometime after I change out the radiator my water pump went out, again I changed the thermostat being sure I had a 190, still till this day it runs just a bit over 180.

Yet I've noticed no ill effects. Can't remember for sure, about 5 yrears back I had to install a new fuel spider, after which I cheked my fule milage on a 100 mile round trip. Fueling up at the same station and same pump going and coming. about 60 miles was two lane roads, about 49 miles was interstate. On the two lanes I drove from 60 to 65, on interstate I set the cruise at just over 70. I got just nearly 23 MPG, at that time it had about 130,000.

When I bought it new in 92, while it was still holding a higher temp, I checked fule milage on a 300 mile trip on two lane roads that less than half was in mountain areas, it got just over 20 MPH. A few weeks later I went to the same place but went around by interrstate getting just nearly 23 1/2 MPG.

1992 S-10 2door 4 X 4 automatic, 4.3 W engine. trailer package