This will probably be the dumbest question that you see on here today, but I have some questions concerning the thermostat on my 98 4.6 F150. The old one that I took out matches the one going in, but once I start tightening the bolts down, the black gasket on the outside of the thermostat starts to bind up, causing it to leak. It also came with an O-ring, but I do not see an obvious place for this to go, and there was not one on the old thermostat. The Haynes manual I have is not much help, as it states to "install the new O-ring into the intake manifold or on to the thermostat housing". It almost looks like the thermostat should fit down into the manifold, but this one sits on top of the manifold (barely). Am I making way more out of this than it really is? I wouldn't think that the thermostat is wrong, since the one that came out is exactly the same.
Thanks in advance.<!-- google_ad_section_end --><!-- / message -->

 

The T stat lays in the intake then the O ring lays on top, it should then be flush with the top of the intake. Here are a few pics:

 

Thank you, the pics help a bunch. My thermostat came with that black gasket/O-ring wrapped around the edge of the thermostat, and that was what was throwing me. The thermostat would not fit down into the intake with it on like that, but according to your pics, it sits on top of the thermostat instead?
It also came with a seperate O-ring. Does that one go between the intake and the thermostat?

 

Sounds like you have the wrong thermostat and gasket.

Buy a genuine Motorcraft thermostat and gasket. RockAuto Auto Parts sells them. The aftermarket ones make a lot of assumptions and design changes that are not called for. They are substituting an universal application thermostat and trying to make it work in a wider array of applications instead of actually making a thermostat specifically for your vehicle. The genuine Motorcraft thermostat will fit better, last longer, and will function properly in your vehicle.

 

you need a vehicle specific gasket. its an orange O ring. costs $2 at napa. the black gasket is for universal applications. there is only 1 gasket. it goes manifold>tstat>o ring gasket>elbow. the tstat sits in the manifold, the o ring goes on top of the tstat, the the elbow bolts down.

 

1 O ring/ gasket and yes it sits on top of the thermostat. IIRC the T stat housing has a little groove that will go down and squish it when it is all tightened down.

 

Thanks guys. I put it back together, without the black gasket, with the O-ring on top of the thermostat, and all is well now, no leaks!
Thanks to all of you on your help!