When I put my new thermostat in, it only had the blue (on mine) gasket.

 

it needs the gasket, and u have to get the thermostat to sit in the slot otherwise it leaves a gap and fluid will come out...trust me, i just went thru this not long ago.

 

wow no kidding I am having the same problem. So your saying to be mind full of getting it in there straight b/c sometimes they do not sit right? I thought it was like a drop in and close up kind of deal. I would love for this to be the fix I am looking for. I have coolant coming from where the flanges meet and it appears to have some coming from the bottom of the upper radiator hose but maybe it just looks that way.

If there is anything specific you did please let me know. I would love to have this problem go away.

Vince

 

What he is saying is very common because the thermostat sits sideways. When you put it together if the thermostat itself slides down just a tad it will create a gap and cause it to leak. I have seen this more times that I can count especially on the 5.0 motors.

Just make sure that the thermostat doesn't slide down. If it does it will leak but look sealed after tightened up.