Coolant Leak Through Hole Under Engine Fill "Radiator" Cap

[TheDudeAbides15]

Hey folks, I've been checking this place out for a while but never posted... now I need a little help. I have a 2006 LS (57,000 miles) which I treat like a total creampuff. With the cooler weather, I noticed it was having trouble reaching temp and after reaching temp would have trouble holding it so I figured my thermostat had stuck open. I swung by Autozone because I wanted a quick fix and dropped $50 on a thermostat housing with a thermostat in it. Did the swap without any problems (the thermostat was the culprit) and started the bleeding process and noticed that after a few seconds I had coolant leaking out from near the cap (through the hotdog shaped hole as it was described in another thread). Long story short, no matter what I did I could't get that leak to stop (I checked everywhere else... it is definitely just coming out of the hotdog shaped hole).

I took the housing back off and checked how well the o-ring from the cap fit in the new housing's tube and it felt like the opening was slightly larger (I then checked against the original housing's opening and it was definitely a better fit). I tried a few different o-rings but I couldn't stop the leak. Am i missing something or did I just get a bad part???

My plan is to just get a thermostat on Monday and use the original thermostat housing but after reading through the threads I could find on the subject I have concerns (I swear the leak is coming through that hole.... the cavity between the cap and the o-ring had coolant in it. Any help would be appreciated, I need the car.

EDIT: Just to be more clear on the area... the hole is under the engine fill cap but above the channel which is supposed to be sealed by the o-ring that is on the stem of the cap...

 

[joegr]

Two choices, I think.
1. Go back to Autozone and buy the engine fill cap that matches the thermostat housing that you bought.

2. Buy the thermostat housing from Ford (probably should get a new fill cap too).

Please note that unless you have recently replaced all the plastic cooling system parts, you will be doing it soon, one after another. It will be a waste of time and coolant to do it that way. It would be much better to get it all now and replace it all at once.
http://www.lincolnvscadillac.com/forum/showthread.php?91092-GenII-LS8-Cooling-System-Overhaul

 

[TheDudeAbides15]

Thanks for the warning... I just need to get the thing running ASAP because the truck I usually drive to work just went down (an explorer with 190,000) and I need some wheels...

I'm certainly going to buy the Ford parts come Monday, I didn't think I would run into any issues swapping a thermostat (swapped plenty in other cars) but apparently I hit a snag. I am always wary of blaming a new part for the issue but I can't see what else it could be. The cap tightens beautifully and all the plastic looks great... the o-ring is just not keeping the coolant out... that cap almost seems pointless anyways...