I am having problems with my 99 Duratec and I hope someone can lead me in the right direction. During warmer outdoor weather my cooling system acted normal (somewhat). The car would cruise at 190F and while idleing would get hotter until the fans kicked on at approx 212F The temp would then drop off to approx 198F and this would cycle back and forth like this . At highway speeds the car would maintain 180ish degrees, all normal except for some reason I thought engines ran cooler at idle instead of hotter. All besides the point. The issue at this point in time is this. Once the outdoors temp went below 25F the car will get up to temp only while driving. As soon as I come to a stop, I can watch the temp gauge drop from 1/3 of the way up to just at the cold mark. This happens in a a matter of minutes. I verified the actual temp drop with my scantool. I do have heat, only not quite as hot as it used to be. I changed T-Stats numerous times last year to get a steady gauge and heat, and it finally ran fine last winter thru summer. Then I though change the o-flow cap. As a matter of fact I changed the temp sensors last year also. This morning I ran the car for 40 minutes and opened the hood and squeezed the upper rad hose while it was hot. What was odd was I was able to squeeze the hose as it had some give to it. Prior to that after running the car, anytime I grabbed that upper hose it was hard and pressurised like a rock, but not now. Does this sound like a lack of 16lbs of pressure to anyone? I ordered a new degas bottle as the fluid level sensor had been flakey. Could this be a pinhole in the o-flow bottle that might be causing this? The degas bottle was bought as a Christmas gift so I cant get it until then. I just seem to think that it is losing/not maintaining pressure. I also replaced the water pump last year. The car dosent seem to be loosing coolant. I had an uoa done last year and that was fine. If it was a leak I would have at least thought I would be able to hear a hiss (If it was the degas). I dont have the cash right now to get it pressure tested. What is everyones take on the cause? In addition, after I refilled my coolant sytem, I leave the cap on when I test it. Is it proper to laeve the cap off after you refill your coolant system or put it on, then run it till you get it to proper operating temp?