Wallnight: I did not mean to say that I replaced everything. I meant to say that I looked at the old threads on this subject and considered the analyses you will find there. My Tstat is only about one year old. My understanding is that if it is working properly the Tstat expands at the correct temp (some dispute about what that is - 85 -104C?) to close the bypass and shunt the collant all to the rad instead of back to the water pump. The CD illustrations are quite clear on this. Therefore if it is working properly you should have a hot top hose after the engine reaches operating temp. If it is not working properly the top hose will not be as hot because the hot coolant is still circulating back to the water pump and engine. If your top hose is hot and the bottom hose is cool, the rad is working. The question is how well is it working? Lots of people know about that simple test, but it overlooks the oil cooler which is the thing I stumbled upon and which I wanted to contribute here. So the answer to your question is that I knew I had a newish tstat, I knew my rad was working but not how well, I knew I did not have pressure in my system when cold so I did not have a cracked block or gasket, I knew my cap was ok because I lost so little fluid on Donner pass, I knew I had the right coolant ratio because I tested that, I did rplace the t sender (no change). I suspected a bad dash gage or an inefficient rad. I now think it was clogged fins in the oil cooler, I may still do the citric acid flush. Don't know