FIX! Coolant on top thermostat housing (Leaky Temp sender) | Ford Explorer Forums - Serious Explorations

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FIX! Coolant on top thermostat housing (Leaky Temp sender)


Explorer Addict
January 25, 2005
Reaction score
City, State
Queens, New York and living in Budd Lake, NJ now.
Year, Model & Trim Level
2002 Explorer XLS 4.0 4x4
I found some fresh coolant (still wet and puddled) on top of my thermostat housing. I was unable to tell where it came from. The thermostat housing also holds the temperature sender. Since the housing was still very wet, I figured there was some seepage after the truck was turned off and coolant system was pressurized.

Starting the truck and squeezing the top radiator hose showed no leaks. Only when I jiggled the sending unit I saw a very small amount of coolant seep past the retaining clip.

The coolant temperature sending unit on the 02 is not screwed in. It is merely held in place by a small retaining clip and sealed by a rubber o-ring. I was able to turn the sender freely and it had lots of play to move back and forth or left to right. I pulled it out and saw that the old o-ring looked like it shrank a bit and was feeling pretty stiff.

From left to right.
Old o-ring
Replacement o-ring
Extra o-ring to make up thickness of original o-ring (second Picture).
Sorry I don't have pics of the sender. I thought of the post way after I fixed the problem.

The o-rings were bought from a 99 cent store. It was an assortment of like 50 or 100 can't remember.

All you have to do is first put in the larger o-ring then the smallest one. I used some petroleum jelly on the rings so they would seat easily and properly when sender is put back in. Last thing before I put on the new o-rings, clean up your sender with a old tooth brush and warm soapy water.
You can use any combination of o-rings you have as long as the sender can be pushed into the housing without much force. The sender should be firmly seated with no play and not be turned easily. Reinstall clip and start truck. Look for leaks after it has warmed to operating temp.


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^^^Great info. Recently changed my tstat housing and have read on other posts that people have issues sometimes when changing or looking for these O-rings. I would like to add that you can also reuse your original O-rings if they're not destroyed and just put a good coat of #2 Permatex Non-hardening sealant on the orings and the housing to prevent leaks. You can also use Permatex on the new orings as well for extra peace of mind. Just my .02 and hope this helps someone in the future.