The coolant will start to boil out from the Denso bottle within minutes of running the engine?

Hi Joe, I may have exaggerated on the few minutes. But it didn’t take very long, between 5-10 minutes. I removed the thermostat from my old housing and ran the truck. It didn’t overheat when I was idling and checking for leaks. I’m going to give it a test run and see what happens. I know about the head gasket being a possible cause but I’m really hoping it’s not. I’ll know after I take it for a test run. The only other thing I haven’t checked or replaced is the ECT sender. I believe that is what signals the computer to open the thermostat or vice versa. There is also a CHT cylinder head temperature sensor right on top in between 2 spark plugs. So actually, it could be one of those or both, the head gasket or the computer itself. I’m off to take a run around the block. I’ll give an update when I get back.

I am aware that the truck will not perform as good without the thermostat. On older cars it wasn’t as big of an issue running without a thermostat unless going up hill for a long time or hauling a heavy load or in the winter time. Here in Hawaii that is not a problem. Steep hills definitely but one could run without a thermostat if they know how to go about the driving conditions.

So, I ran her a couple miles up a steep hill with no issues. When I got back, I popped the hood and was able to touch the upper and lower hoses. They were both about the same temp with the lower one a slight cooler. That rules out the head gasket (whew) DOHC are not fun to change a head gasket. So, it’s down to a faulty sensor or sending unit or both. I think if it was the computer, it would be running fun but it’s running as it did before this problem.

The truck is running good, no issues so far. I did some research and found out that ford added the heat assist thermostat thinking the engine would need it to help the thermostat open sooner since that particular engine was originally used in front wheel drive cars where it sits sideways in the engine bay. After 3 years they realized that it was not necessary, so they did away with it on the 2004 model and up. So, I’m going to get the water outlet and thermostat for a 2004 model. It is the exact same part minus the “heat assist “ plug so it will bolt right up. The check engine light will stay on. A resistor hooked to the two wires will take care of the engine light. I think I will go with the 180-degree thermostat since the outlet is on the bottom hose not the top that should keep the engine in normal operating temperature and allow proper warm up process. As of now the gauge only reaches the C and it takes a couple miles of driving to reach that level.