Originally Posted by mgc1963
the t-stat does have the rubber seal on it. If I replaced it 3 times with no improvement, why would you suggest I do it a 4th?
Because it was my understanding that the problem would be resolved, and then return. Reviewing your post, I find that assessment to be mistaken.
Now, I am proceeding under the assumption that the vehicle is not actually coming up to temperature. The thermostat controls how cold the engine can run. As long as it has a proper seal, there should be no coolant going through it. I will run down the possibilities, and you pick which ones may apply.
O-Ring not properly installed/seated, allowing coolant to flow right past the sides of the thermostat. You indicated it was properly installed each time, that'* great.
Wrong thermostat. You know, wrong size, for the wrong engine, etc. I hope this is not the case as you have replaced it twice so far.
The thermostat is locked open. Many advertise Fail Safes, which lock open if the thermostat opens wide enough. Could also simply be stuck, etc.
One scenario comes to mind. You install Fail Safe thermostat. You start engine and let it come to temp, only to have a giant air pocket behind the thermostat. The engine becomes raging hot, and you have no indication. The thermostat finally opens, and releases the air pocket, and the raging hot coolant hits the thermostat, and trips the Fail Safe. You have now just killed a brand new thermostat on your first start, it stays open, and you continue to curse the car.
Something else that was mentioned to me elsewhere, was thermostat orientation. You sure you didn't put it in upside down?
One thing I would be inclined to do is check the running temp of the car using an external means. I use an infrared thermometer on the thermostat housing. This confirms the car is actually running cold. If it is coming up to temp properly, you may want to check the temp sender unit (I believe there is two, but am not sure), the dash gauge, and for your lack of heat, the air mix actuator (a common failure point actually).
Others like to check the thermostat operation by sticking it in a pot of water on the stove, and checking what temp it opens up, as compared to what it should be.