I got half way to work this morning and noticed my engine temp gauge had maxed out. Coolant appeared to be leaking from the resevoir due to being over pressured. The resevoir was still full. After about ten minutes, I started the engine and the temperature gauge was reading normal. So, I think I have a sticking thermostat and bought a replacement with a new o-ring. I wasn't paying attenstion when I removed the old thermostat and o-ring (kids fighting) and can't remember if the o-ring rests above or below the thermostat. The Haynes manual's picture is too dark to tell but it looks like its below but the Ford manual's diagram makes it look like the o-ring is above the thermostat. Any help?

Thanks

 

My ford manual also shows it on top.

 

The diagram shows it going on top but if you read the procedure, it sounds like it goes in before the thermostat.

 

I tried a modification to your flush procedure by also removing the lower radiator hose and using a garden hose to flush from the upper. I'd flush until the water ran as clear as possible, start the engine with both heaters on, stop the engine and re-flush.