Dorman thermostat housing o ring leak fix. Help!!! | Ford Explorer Forums - Serious Explorations

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Dorman thermostat housing o ring leak fix. Help!!!


New Member
October 5, 2013
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Year, Model & Trim Level
2004 4.0 v6 Explorer XLS
So I replaced my thermostat housing unit today with the dorman aftermarket kit and the o ring in the extra port is leaking badly. I've seen this is a common problem through research but nobody lists the fix. I have tried both o rings that came with the kit to no avail. It is only leaking from the extra port where the plug is installed. Please help!

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I replaced that part about a year ago and you must make sure that the o rings are properly snapped into place or it will definately leak. I used a little bit of vasoline and kept playing with the sensor until it properly seated. It was time consuming for such an easy fix, and very frustrating, but keep working at it and it will eventually seat.
Good luck

I had the sensor fully seated and I believe the o ring may be the wrong size. I read a lot of reviews on advanced where I purchased the part.

Too late to exchange for the OEM Motorcraft RH148 one sensor lower housing? Only
other parts needed are lower and upper o-ring seals, and a new ECT sensor o-ring.

I had the sensor fully seated and I believe the o ring may be the wrong size. I read a lot of reviews on advanced where I purchased the part.

Did you wet the new O-ring with some coolant prior to seating the port plug into the Dorman t-stat housing? This is the proper way to "seat" the O-ring and sensor or port plug. Did you also remember to slide the "metal retaining clip" back into place around the temp sensor and port plug once it was seated into place? You need a retaining clip for both the temp sensor and port plug to keep them from separating from the housing. The O-ring itself will not hold the sensor or the port plug in place in case you didn't know.
I changed the t-stat housing last May 2013 on my old, original motor, using a new Dorman t-stat assembly and a new BWD temp sensor. The BWD temp sensor came with it's own O-ring already installed around the sensor and although it was a tight fit into the assembly, took some force to get it to "pop into place", it was fine afterwards, no leaking at all. The Dorman t-stat assembly I bought came with only one O-ring and one extra port plug. I used the Dorman O-ring with the Dorman port plug. The Dorman O-rings that came with your Dorman t-stat assembly should be sized properly for that assembly, both same brand.

I ended up buying a new sensor and it finally fixed the leak. My housing came with 2 o rings neither of which fit properly. I had to buy a thin 9mm o ring to supplement the one that was installed already on the plug to get a good seal. The o ring for the temp senso I had was flattened I'm assuming from being years old. The new sensor I bought seals great though so i should have avoided this headache altogether and bought the sensor from the start. Thank you everyone for help. It was much appreciated.