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How to: Replace a thermostat in an Aerostar.

BrooklynBay

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Year, Model & Trim Level
88 89 93 95 96 Aerostars
We've had some nice warm weather this summer in NY this year. My 1995 3.0L van's temperature gauge usually rests in the middle during normal driving. Lately it's been warming up faster than usual, and during acceleration it's been climbing up a little too much. Last week it actually hit the H on the gauge even though I had the heater on to help cool it down! :fire: I don't know how old the thermostat is since I'm not the original owner, but I would assume that it might be the original just like most other things on this van. These are the parts which I chose to use since I originally purchased each one for a different vehicle a while back, and never used them:
Performance_thermostat_with_a_special_gasket_.jpg

This gasket cost more than the regular paper gaskets but it's much better quality. You don't have to use any gasket paste, and it's ready to use immediately. It's much thicker than the thin paper gaskets.

I had to use caution while removing & reinstalling these old bolts since they were very hard to turn with a 3/8" drive ratchet. I didn't want to strip the engine block threads or crack the bolts off. One trick is to keep reversing the direction while you turn the socket whenever it gets stiff. Tighten the bolt, then loosen it a little until it feels free, then tighten it again until it feels stiff, then reverse it again. It will take longer to do but it's a safety precaution. Here's the first bolt removed:
The_first_bolt_is_coming_out_.jpg

There's very limited room to work. I didn't remove the upper radiator hose. I left it attached to the upper thermostat housing with a hose clamp, and moved it aside after I got the second bolt out.

The second bolt is a littler harder to reach but still possible to disconnect without removing any parts:
The_second_bolt_is_a_little_harder_to_reach_.jpg


The thermostat housing lifted off easily but the thermostat was stuck to the gasket:
The_top_housing_is_off_.jpg

A little coolant spilled out but not too much when the housing was removed. I had to tap the thermostat a few times to get it loose. The temperature on it says 197 degrees, and it has a small hole to bypass fluid just in case it gets jammed. This is a failsafe thermostat. It allows a small amount of fluid to pass through even if it jams.

Make sure that the new thermostat has the curved point facing up when it's installed. Place the gasket inside next then put the housing back with the bolts. Don't completely tighten one bolt before you install the next bolt. Go back & forth to each bolt to tighten them, then refill the correct mixture of coolant into the radiator while the engine & heater are running. Reinstall the cap, and keep the engine & heater running while you check for leaks.
 
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don-ohio

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March 22, 2013
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City, State
jackson,ohio
Year, Model & Trim Level
1994 Aerostar extended
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 :)^)
 
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BrooklynBay

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don-ohio

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jackson,ohio
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1994 Aerostar extended
Do you know what the temperature range is on the new thermostat? How does the temperature gauge look with the new thermostat? Did you use a fail safe thermostat?

Yes,sorry I didn't see your post. The gauge shows about one fourth of the way to hot.It is a 192 degree and it's NOT a fail-safe.
Ida'had to order that one,so I went with a regular STANT. The guy at Advance Auto said that the fail-safes go bad more often and sooner than the regular ones. My heater is toasty warm now! Actually,it's HOT!don-ohio
 
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Joined
January 22, 2019
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Location
Pacific Northwest
City, State
Portland, OR
Year, Model & Trim Level
1993 Aerostar XL 3.0
Thank you for this write up. I am going to do this Sunday, and other than limited space, seems pretty straightforward.

Just need to buy the parts and a simple tool set, everything I have is in storage 3 hours away.
 
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don-ohio

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jackson,ohio
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1994 Aerostar extended
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Joined
January 22, 2019
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Location
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Portland, OR
Year, Model & Trim Level
1993 Aerostar XL 3.0
Question!

I went to change my thermostat last night, and everything went fine, until I started up the van. Garage got a nice shower of coolant.

I un-did the housing again to make sure everything was set right, I had pinched my gasket and it created a rip!!

I'm going to buy a nicer gasket today and finish it after work. I just want to make sure, it goes: Install thermostat THEN replace gasket over new thermostat / re-install housing, etc...
 
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BrooklynBay

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City, State
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Year, Model & Trim Level
88 89 93 95 96 Aerostars
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Joined
January 22, 2019
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Portland, OR
Year, Model & Trim Level
1993 Aerostar XL 3.0
Use the dry seal gasket that is in the first photo of this thread. It cost a little more than the regular gasket but it's worth it.

I went ahead and bought a new, thicker rubber gasket like the one shown above, and it's working great.

I also changed my ECT sensor, and it's still reading cold and now my check engine light is on. Maybe a bad sensor?

The one I removed crumbled in my hand!!
 
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BrooklynBay

Moderator & long time member.
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City, State
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88 89 93 95 96 Aerostars
The ECT sensor is for the engine since it has two wires. The temperature sender for the guage has one wire. You could test the wiring for the temperature sender if you ground it against the engine block.
 
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Joined
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1993 Aerostar XL 3.0
The ECT sensor is for the engine since it has two wires. The temperature sender for the guage has one wire. You could test the wiring for the temperature sender if you ground it against the engine block.

Grounded the sender, and the gauge went all the way to hot on the dash, so I believe that's a good sign.
 
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Adam_tinkerer

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City, State
Newton, NC
Year, Model & Trim Level
1992 Aerostar
I'm going to add that most of the aftermarket thermostats aren't very long lived. I replaced mine, and within a year or so it wasn't working properly. I found nos Motorcraft versions on ebay, bought two just in case. I haven't replaced it yet, I started a new job last August, and got a co. work truck. I rarely drive the Aero anymore.
 
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don-ohio

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1994 Aerostar extended
Something has happened to aftermarket thermostats the last several years. Not nearly the quality of Factory parts. Get the Motorcraft to do it right.
 
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