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Thermostats
Jeep Grand Cherokee

How do you replace the thermostat in a 1997 Grand Cherokee 4.0?

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April 18, 2012 4:40AM

The Jeep (Grand) Cherokee 4.0L motors all have the thermostat in a dedicated housing at the top front of the engine, held in place by two bolts. In principle, one could remove the thermostat housing simply by disconnecting the upper radiator hose (a simple hose clamp holds it onto the housing outlet pipe), and then removing the two bolts and wrestling the housing out past the radiator fan shroud.

In practice, its much better (and likely faster!) to:

-- disconnect the wire harness feeding the temperature sensor on the upper left of the thermostat

-- remove the four nuts retaining the fan assembly to the water pump shaft flange

-- then remove the two nuts at the upper edge of the plastic fan shroud

-- finally jiggle the fan/clutch assembly forward off the water pump shaft flange studs towards the delicate radiator fins and slide the fan assembly and fan shroud upwards together

-- drain the coolant down into a bucket by using the radiator drain cock or pulling one end of the lower radiator hose.

-- disconnect the upper radiator hose at the thermostat housing.

-- remove the lower thermostat housing bolt; it's tucked behind the serpentine belt, so you might need to loosen the power steering pump tension adjusting bolt to get the belt loose enough to allow the bolt to be removed [how to loosen belt is model dependent...]

-- remove the "upper" (its really more in the center) bolt of the thermostat housing.

-- gently pry/tap the thermostat housing off the head with a large screwdriver or soft mallet (to avoid leaks, the housing is often installed with excess gasket goo).

-- the thermostat is tucked completely inside the housing, and will usually come off with the housing.

Installation is largely the reverse...

-- carefully clean both the thermostat housing gasket face (remember, its soft aluminum, and your gasket scraper--you wouldn't use a screwdriver, would you?--is steel) and the engine head face.

-- use whatever gasket goo you prefer that is temperature rated and coolant rated to coat both engine head face and housing face

-- apply the new gasket to the engine head face (it will stick because of the goo)

-- gently align the thermostat in the housing (get the correct side "in") and place both together against the engine head face, being careful not to get gasket goo on the thermostat proper

-- reinstall the center bolt

...

-- reconnect all the hoses (if you can't remember when you changed them, buy new ones)

-- replace the coolant as best you can, topping off the overflow tank so it will have plenty to suck back into the system which is now cursed with extra air rather than coolant

-- sliding the fan and shroud back in takes patience in many models... it can be like a 3D Tetris puzzle:-(