Coolant leak between engine and fire wall

[JayD801]

2004 Lincoln LS ultimate. Upon startup leaking coolant from the rear of the engine but then stops leaking within a couple of minutes . I have already replaced the radiator the water pump the thermostat the coolant reservoir. I don't hear any air bubbling coming from the reservoir the heater works just fine and after startup at leaks a little bit but then I can drive the rest of the day without any leaks that I'm aware of. If anybody has any kind of idea of what I'm looking at here please let me know

 

[joegr]

Look at this link:
REPLACE YOUR COOLING SYSTEM - 2004 Fun and Easy Steps
And this one:
GenII LS8 Cooling System Overhaul

Your leak is one of the parts that you didn't replace. You really have to replace all of them at once. Note that leaks at the front of the engine will run under the intake manifold and come out at the back of the engine.

 

[SultanGris]

Likely the hose under the intake that goes to throttle body, that's what was leaking off the back of mine, or the plastic neck behind the thermostat.

And Joegr is correct, I replaced mine one at a time and the next one kept failing. However I was short on cash and doing the work myself so it bought me lots of time cause none of mine leaked too bad, if you gotta pay someone to do it then do it all at once for sure cause I took many things apart multiple times to get to the next failure, the labor will kill ya if you have to pay someone to do it that way.

 

[04_Sport_LS]

Most likely the large O-ring on the back of the crossover, (head to head), pipe where it fits on the elbow that mounts to the top of the engine block.

When that O-ring fails... the coolant runs along the top of the block... and down onto the transmission.

 

[04_Sport_LS]

 

[04_Sport_LS]

The pic is from the passenger side of the crossover pipe... looking under the throttle body plenum.

 

[04_Sport_LS]

I'm gonna guess that when you replaced the thermostat... you pulled the crossover pipe on the engine... and re-used the large O-ring on the elbow... or bought an aftermarket O-ring.

A new factory Ford/Motorcraft O-ring needs to be used... and putting a little coolant on the O-ring before installing the crossover pipe... helps the O-ring to seal and fully seat in the backside of the crossover pipe.

 

[JayD801]

Likely the hose under the intake that goes to throttle body, that's what was leaking off the back of mine, or the plastic neck behind the thermostat.

And Joegr is correct, I replaced mine one at a time and the next one kept failing. However I was short on cash and doing the work myself so it bought me lots of time cause none of mine leaked too bad, if you gotta pay someone to do it then do it all at once for sure cause I took many things apart multiple times to get to the next failure, the labor will kill ya if you have to pay someone to do it that way.

You was spot on- the plastic neck behind the thermostat housing is leaking coolant down the block and dripping out behind the engine. I'm very impressed with this site and the members knowledge of the force would make Yoda proud !!! ( Sorry for the Corny reference to star wars ) You have made a believer out of me and I look forward to hearing more educated advice from my fellow LS owners... Thank You