"How To" thread - replacing entire thermostat assy? | Ford Explorer Forums - Serious Explorations

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"How To" thread - replacing entire thermostat assy?

Team Chepsk8

Well-Known Member
November 7, 2010
Reaction score
City, State
Easton PA
Year, Model & Trim Level
2001 Explorer Sport Trak
I may have to replace that assembly, as I to have the smoke for the intake area, and coolant leak.

Is there a "how to" thread which describes doing this?

Many Thanks

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nice info, thanks.

I priced a new assembly at the Ford dealer, over $300, yikes!!! any other places, or dealer only?

If it's warped, can I block sand it?



I got mine at the local O'Reilly parts store. Paid $150 for it. Here is the specific info on it Dorman - Coolant Thermostat Housing Part # 902-204. I also replaced the senors as the old ones wouldn't come out. Found out the temp sensor was wrong one after I got it back together again. So be sure to double check and make sure you have the right sensors if you buy new ones. Once I figure out what the right one is I'll take it back apart and fix it.

Has anyone had the assembly apart just to discover an O-ring problem? I do have the smell when accellerating, and slow loss of coolant, so it does point to an problem in that area.

I just did a repair on my other Ford, a 98 XZ2 which also had a coolant leak around the plastic housing, and it was a definite O-ring problem. I am not afraid of tearing it down, just not in the position to drob the big money unless I have to.

I did the job on my friend's '01 - the other day. The lower housing was leaking from the joints between the layers. Ford parts were purchased from Rockauto.com for around $70.00. I also replaced the hose that connects the lower thermostat housing to the water pump outlet since it was just a matter of removing one more clamp.

Make sure to buy new o-rings for the coolant temperature sensors. Ford makes you buy the whole sensor just to get the o-ring which is BS as far as I'm concerned....

The O-ring size is 9mm ID and 2.5mm wall thickness. A hydraulic shop can get o-rings made of viton which will resist temps up to 450 degrees which is about double the temps the cooling system will ever see.

I just purchased the two O-rings, the lower one looks like a black rubber band. Is this correct?

There should be one o-ring on each sensor. The old ones will look flat from years of being installed but the new ones should be round in cross section.

I measured an o-ring fro a new coolant temp. sensor to obtain the dimensions in my earlier post. 9.0 mm inside diameter, 2.5mm wall thickness. If that does not provide a good enough seal, you could try 9.00 ID and 3.0 mm wall thickness.

Use o-rings that are made of Viton as that will have the correct temperature resistance for the application.


Thanks for the reply, though the O-ring in question I was referring to was the one between the the intake manifold and the thermostat housing.

Does my description sound familiar?

Sorry about that - Yes - the o-ring between the intake manifold and the lower thermostat housing looks like a black rubber band and it fits into a groove in the lower thermostat housing. It is available from the Ford dealer or Napa. The thermostat seal is just an o-ring - available at Napa for less than a buck.


thank you very much! I wanted to confirm I had the right one before tearing everything apart.:rolleyes:

Make sure you have new o-rings for the coolant temperature sensors before tearing it apart as you will not be able to reuse the old ones - they won't seal after years of compression set in the old housing.

I also recommend replacing the hose clamp on the heater hose also as the old one is in an awkward spot - I ruined mine in the removal process.

It is also a good idea to replace the bypass hose that leads from the thermostat housing to the water pump outlet too - it is a $6.00 item from Napa and it's just worth it to replace it as if that hose goes bad, you need to remove the water pump or the thermostat housing to replace it.

Are the two small O-rings for the sensors available not from a dealer? The dealer wanted over $20 each, agad!!!!

Who else carries them?

Team Chepsk8,

I don't think the o-rings are available separately from the dealer - they want you to buy new sensors. Mcmaster.com has a selection of o-rings in viton or you could try a hydraulic shop. The inside diameter is 9.0mm and the wall thickness is 2.5mm. I measured them off a new sensor.

Make sure when purchasing o-rings, they are viton and that the size specified is the actual size of the o-ring. You may want to buy a couple of 9.00 ID and 3.00mm wall thickness also in case the 2.5mm ones don't provide a good seal.