Front of Motor coolant leak when starting in COLD weather only

[Team Chepsk8]

Been working to isolate a troublesome leak. Last two Winters only (in the Northeast, sub-freezing outdoor temps). It will piddle about a half-cup of coolant when first started, and only the first cold start. A start later in the day it does not leak. Just replaced the water pump,bypass hose, and all clamps. No leaks on test drive, but leaked again the next cold morning. A few years back, replaced the plastic thermostat assembly. Truck runs on the thermostat temp, and does not overheat or run warm at any time, even Summer.

Looked at it this morning when it was dripping, seems to be on the passenger front/center side of motor.

So, I can rule out the water pump.

Can it be:
Head Gasket?
Intake Gasket?
Thermostat housing? (I HATE that stupid plastic assembly and ridiculous rubber-band O-rings)
Something else?

Should I pressure test it?

Should I try a cooling system sealer, and if so what type?

I appreciate any and all suggestions, and really want to hear about similar instances and the following solution.

The truck has 222,000,never a big problem,never had the motor apart, still runs smooth, no oil leaks, cannot discern if there is any extra steam in the exhaust, though I did check for bubbles in the radiator when hot and running, none. Motor is the 4.0 SOHV, truck is a 2001.

Thanks you in advance, this forum usually is able to come up with a viable solution!

 

[swshawaii]

Pressure test first, sounds like your replaced lower thermostat housing let go. Here's the new aluminum lower and upper.

http://www.explorerforum.com/forums/showthread.php?t=362922

 

[joecrna]

Agree, probably the thermostat housing again.

 

[Team Chepsk8]

Agreed, time to pull it apart again up there. Is that O-ring available separately? Should I use any sealant when re-assembling? I will also deck check and flatten all flat surfaces.

 

[Team Chepsk8]

I am wondering of the upper house/thermostat top part of the housing is the culprit? It has the green crud at the split, and I looked over my old one and am wondering if it just never sealed tight? Could the metal sleeves that guide the location be a fraction too tall, and prevent the housing from fully clamping the O-ring and sealing?

I have two new O-rings, so will first just focus on the top part before pulling the whole assembly out.

Saw that thread for the Mustang housing and posted for any updates. Any other metal housings available?

Been doing some searching, see many housings available, all in the $50 range. I see a Dorman with an improved bottom O-ring, which I like the idea. Mine is a SOHC motor. Which replacement assy has proven to be the best, and is that improved bottom seal available for my motor?