How do I tell if my thermostat is functioning correctly? I am not boiling over, but I suspect that the thermostat is not opening all the way. I am running a 180 in a L78 396.

well on normal startup and driving you would watch your temperature gauge, if it creeps up to 180-185 and stays there for awhile then its opening and functioning, if it cruises past 180-185 without a whimper and heads to 190-210 without skipping a beat then its not opening properly and can be replaced for about $4

I don,t have a temp guage in the car so I am looking for another way. I was told that the upper hose getting hot and firm indicates that the therostat is working. My concern is that the thermostat is only partially opening or sticking after the car is warmed up and sits for an hour before re-starting. The car seems to be fine during initial start-up but after the car sits at a curise for a few hours and I drive it home (3miles) the car seems to really warm up. Help!

Place your thermostat in a pan of water on the stove. Place a thermometer and the thermostat in the water and bring it to a boil. Any temperature over 180-185 degrees, the thermostat should be open. REmove evidence before the cook gets home.

You are going to have to put a temperature gauge in if you want to really know what is going on...otherwise you are chasing a phantom!

Making decisions on seat-of-the-pants feelings can point you in the wrong direction. There should be no reason that a "few hours" isn't considered a completely cool system.

And.....how do you know it warms up "fast" if you do NOT have a gauge?

If you want a quality thermostat that will NOT stick closed order a Mr Gasket from Summit. Impossible to stick shut without mechanical interference. High flowing too! :D