Re: 2001 Jeep Cherokee XJ. Let me preface this my stating due to a suspected heater core leak I bypassed it with a 3/4" heater hose on the outlet at the thermostat housing (and it loops back into the other end which is a metal tube to the water pump area).

A week or two ago, I noticed the area around the thermostat housing right below the heater hose had a couple of green droplets of coolant, so naturally I tightened the hose clamp some more. However, overnight I found a damp spot on the driveway due to the very same seepage.

This second time I removed the hose and cut off one or two inches of it where it had been held on to the metal (aluminum?) stub outlet of the thermostat housing (and smashed a little) by the hose clamp. With a "fresh" end of the 3/4" heater hose, I then attached it with a new hows clamp this time and only after sanding off the whitish "crud" that I found on the thermostat housing heater hose stub/tube. I tightened the clamp all I could using a large blade screwdriver (I could have used a 5/16" socket, but I didn't want to overdue it). It sat overnight only after I tied a very small strip of blue paper towel around the heater hose outlet stub immediately below the hose (and actually touching the hose). My idea was trying to figure out if the coolant was getting past the hose, regardless of all my efforts, or if perhaps the thermostat housing itself had a hidden crack somewhere or if it even could have become porous enough to cause a drip.

Now this morning I find a very small coolant stain on the driveway and i can see two or three green drops of coolant on the bottom half of the thermostat housing which have originated either from the heater hose or somewhere immediately surrounding the heater hose. The little strip of blue paper towel is damp, but hard to tell if it became so by soaking up coolant from below and from getting damp from a drip from above. So much for my idea.

My questions are these:
1) Is the factory heater hose in the area of my seepage a 3/4" diameter hose or maybe something smaller? I would think even if my hose was slightly larger in diameter, the hose clamp would certainly close it off anyhow. But maybe that assumption is incorrect?
2) Do the 4.0 Liter motor thermostat housings







have a bad reputation of cracking or becoming porous?

Thank you.

 

Did you wash off any residual coolant before the overnight park test? Despite having cleaned the housing, there can be deep pitting that prevents good seal.

 

I used brake cleaner to clean/dry the area.

 

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I would guess a wrong diameter would cause issues, even when tightened up as much as possible. I do think this is the culprit.

I haven't heard of the housing cracking.

 

According to my research, the heater hose outlet at the thermostat housing is indeed 3/4" and that connects to a heater core inlet of 5/8" so the factory hose is different diameters on each end. I had already bypassed the heater hose (as stated above) by using an adaptor between a length of 5/8" and 3/4" hose. So what i tried for now was to forget the screwdriver and whip out my 1/4" drive ratchet with a 5/16" socket to fit the new hose clamp. I cinched it down pretty much as much as I could. I now am going to run the engine up to operating temperature, turn it off, and let it sit all night again and hope for the best (please, no more drips!).