Changing a thermostat on 1998 chevy c-1500,can I just remove the old one and reattach the hose.the truck temperature is only 160.

follow the lower radiator hose to the engine,you have to raise vechicle to see thermostat it is under the vechicle,the thermostat is in the housing where hose go to thermostat housing bolted to the engine, you need to remove hose.if you have the HEMI ENGINE follow top radiator hose to thermostat housing behind the AC COMPRESSOR.

Hi there:

It is located at top front center of engine:

Remove radiator upper hose and heater hose at thermostat housing.

Disconnect wiring connector at engine coolant temperature sensor.

Remove thermostat housing mounting bolts, thermostat housing, gasket and thermostat. Discard old gasket.

Clean the gasket mating surfaces.

To install:

1. Install the replacement thermostat so that the pellet, which is encircled by a coil spring, faces the engine. All thermostats are marked on the outer flange to indicate the proper installed position.
2. 
   
3. Observe the recess groove in the engine cylinder head.
4. Position thermostat into this groove with arrow and air bleed hole on outer flange pointing up.
5. 
   
6. Install replacement gasket and thermostat housing.

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

/Replace Thermostat- approx. 11.99 Gasket-1.69- 3.99 sealant-3.79

CAUTION
If the radiator is filled to the top with coolant and the engine is run without the radiator cap in place, the coolant will expand and spill over as the engine warms up.

• Drain some coolant into a clean container until the coolant level is below the thermostat housing.
• Remove the upper radiator hose connection from the thermostat housing.
• Loosen the housing bolts and remove the housing.
• Remove the gasket and scrape it carefully from the surface of the housing and the mounting surface on the engine. If the gasket remains on either of the surfaces, there will probably bea coolant leak after reassembly. Some engines use a rubber O-ring to seal a thermostat housing.
• Compare the size of the thermostat to the old one. They are of different sizes, types, and temperature ratings.
• The temperature rating is stamped on the sensing bulb on the bottom of the thermostat. The temperature bulb faces the block.
• When replacing a thermostat, be sure that the thermostat fits into the groove in the block or outlet housing. If the thermostat is installed upside down, the engine will overheat.
• Install the gasket.
• Reinstall the thermostat housing. Refill the system and run the engine or pressure test to check for leaks.
• When the engine has reached operating temperature make sure the thermostat opens.
• You should be able to see coolant circulating within the radiator.
• Another way of checking thermostat operation is to feel the top of the radiator hose or use a thermometer or multimeter with a temperature probe to confirm that the coolant is warming up.
• If the engine is overheating, but the top hose is still cool to the touch, the thermostat is stuck closed and must be replaced.

NOTE When a paper gasket is used and the recess is in the thermostat housing, it is a good practice to position the thermostat into the recess and glue the gasket to hold it in place. If it falls out of its groove during installation, the outlet housing can be cracked or a coolant leak will result. Before tightening the water outlet housing, try to rock it back and forth to be sure it is flush. Housings are often cracked during this step.

first you need drain engine coolant down below thermostat. what engine type 3.8 or 3.4 need to know.the 3.8 engine thermostat housing on top intake follow top radiator hose to thermostat housing.the 3.4 engine you have to remove air filter housing with air inlet duct with mass air flow sensor.you have to remove throttle body with coolant hoses.go to auto parts store buy new throttle body hoses old ones will be hard to remove might have to cut two small hoses also buy new throttle body gasket also. before you can remove throttle body unit you have to remove accelerator cable and downshift cable from bracket bolted to throttle body.once throttle body remove then you can remove thermostat housing bolt remove replace thermostat.

Trace the upper radiator hose toward the Grand Cherokee's engine until you reach the metal component connecting the hose to the engine -- this is the thermostat housing. Find the coolant temperature sensor -- the electrical component on the thermostat housing. Press the locking button on the coolant temperature sensor wiring harness and pull the wiring harness from the sensor, then remove sensor it screws out. when putting in new sensor coat the threads with teflon pipe thread tape so there is no leaks.

the thermostat is in the housing where the top radiator hose connects to the engine !!!!
1. remove the top radiator hose from the housing
2. remove the bolts that hold the housing together ( be careful NOT to break them off )
3. remove the old thermostat
4. remove the old gasket with a suitable scraper & clean both surfaces of the housing with the scraper or sandpaper
5. fit the new thermostat & new gasket
6. put the housing back together & replace the bolts being careful not to over tighten
7.replace top radiator hose & tighten clamp & fill radiator with water
8. start engine & run to reach normal running temperature & check for leaks
hope this helps......cheers.

A repair manual would be a good idea, However, follow the upper radiator
hose to the engine to locate the thermostat housing. Drain the coolant,
remove the hose, the thermostat housing, make sure you note how the
thermostat is installed before removing it, clean all mating surfaces, install
new thermostat and O ring, reattach all and replace coolant.

Follow the upper Radiator hose from the radiator back to the motor. remove the hose on the motor end and then remove that coupling that it was attached to. The thermostat is under that coupling. Remove the old seal and any remnants of that seal, put the new thermostat in place, put the new seal in place and bolt the coupling back down and reattach the hose, top off the radiator and test drive.

The thermostat is in a difficult position. Follow the upper radiator hose and it leads into the block under the throttle body. 
Remove the air filter assembly and you'll c what is the exhaust manifold crossover pipe right in front of the thermostat housing.
 NICE, it gives you very little room to remove the 2 bolts to the housing and once u remove those then you'll find you have the thermostat housing loose but because of that darn exhaust manifold crossover pipe u don't have enough room to take the thermostat housing out to change the stinking thermostat. 
So from what you can see, you have to remove the heat shield which is cased around the exhaust manifold crossover pipe and if you still can't get enough room to remove the thermostat, (which you amy find out)then you'll have to remove the crossover pipe as well just to change the thermostat. 
If you have to remove the crossover pipe then their are 2 bolts on both ends of the pipe leading into the manifolds. But then the tough parts done and once u switch the thermostat over and ATTENTION:remove any old gasket material and put a new gasket in it's place then installation is reverse of removal. 
Good luck and hope this helps,

the thermostat is located where the upper radator hose comes off the engine there are two bolts or nuts remove hose and remove housing you will see the thermostat when you do clean old gasket material off block and reverse removal procedure