Cooling Question - First Gen.

[Bronco648]

Factory parts in this picture, no idea how to keep that ring in place while tightening it down.

It's interesting but the O-ring I installed was slightly too big to fit into the t-stat opening in the water pump body (Fel-Pro IIRC). I may have discovered the solution by mistake. Initially, I installed the O-ring and gasket backwards. I then looked at the image I posted and discovered my error. By that time, the Permatex form-a-gasket had begun to set-up. So, the O-ring ended up getting 'glued' to the flat gasket. I believe that's what's holding it in place.

Additionally, I think the 'bridge' on the t-stat needs to be oriented vertically (90* from what's shown in your image). Why? Because the water neck, that bolts to the water pump, brings water in from below. So, if the O-ring happens not to seat properly, the bridge will prevent the coolant from 'washing' the O-ring into the t-stat opening (when hot) which would create a (partial) restriction.

 

[Bronco648]

Two Week Follow-up

The cooling system has been working very well. We've had temps near 50* and temps below freezing. I can hear the fan kick on/off so I know the t-stat is opening and closing and coolant flow must be better. At this point, I'm pointing the finger at an improperly installed t-stat O-ring. It must not have seated properly and was partially obstructing the coolant flow thru the t-stat.