I need help finding & replacing the thermostat on my 4.0L 1997 Aerostar. | Ford Explorer - Ford Ranger Forums - Serious Explorations

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I need help finding & replacing the thermostat on my 4.0L 1997 Aerostar.


New Member
November 6, 2019
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City, State
Year, Model & Trim Level
1997 Ford Aerostar 4.0L
I have only been able to find information on the 3.0L thermostat location. My vehicle is a 4.0L and I can't find the thermostat. It has been running cold with the temperature only moving up a little even on the interstate but the heater still works good. Runs pretty roughly though with stalling at idle and I think it may help to have a warm engine.

Josh P

Shaggin Wagon
Elite Explorer
February 18, 2015
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City, State
Phoenix Az
Year, Model & Trim Level
1991 aerostar
I'd suspect the coolant temp sensor has failed. The thermostat is behind the serpentine belt tensioner.


Moderator & long time member.
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Elite Explorer
November 11, 2005
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Brooklyn, NY
Year, Model & Trim Level
88 89 93 95 96 Aerostars


Well-Known Member
March 22, 2013
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1994 Aerostar extended
Welcome to this forum! The thermostat is in the housing where the upper radiator hose meets the engine.

Blast from the past!
I just did the thermostat on my 4.0,Brooklyn! No pics,but here's what I remember....
(1) Disconnect battery cable because of airbag.
(2) Remove cover over throttle linkage.
(3)Remove air cleaner tube between air filter box and throttle assembly.
(4)Heater hoses are blocking access to thermostat housing....remove a 5/16 screw and they'll move just enough out of your way.
(5)Drain coolant into clean pan if re-using.
(6) Remove hose from thermostat housing.
(7) Loosen the drive belt and get the tensioner out of your way.I replaced MY tensioner anyway,since it seemed weak.
(8)Now you can remove the THREE 10mm bolts and get the thermostat housing loose.
(9) Remove old thermostat and gasket and clean the engine and housing surfaces.
(10) I put the new thermostat in the gasket and used red silicone gasket sealer on the back of the gasket(let it age a few minutes) to hold it in place while I positioned and bolted the housing so it wouldn't slip.
(11)Start tightening bottom left bolt first and alternately tighten the three until you get them about 15 lbs. torque. each. I used never-seize coating on my threads when reassembling.
(12) NOW attach the upper hose and fill up the radiator because if it's gonna leak you wanna know now,not after you put her all back together,right?
(13) If no leaks,reassemble in reverse order of removal.
(14) Don't forget the small hose which plugs into the large tube of the air filter assembly.
(15)MOST IMPORTANT! Run the engine with heaters(both front and rear if equipped)with temp turned to high.Rev the engine a little and shut her down and check the radiator level again.You might have to do this twice. When you're satisfied you have the air out of the system,check the level of the expansion tank and make sure it is at least 2/3 full with engine hot.
That's it! don-ohio :)^)