Originally Posted by BK_in_NH
I had this exact problem. Took me a long time to figure out the cause but here is how I finally fixed it :
There is a small (5/16"?) hose that starts starts at the upper radiator hose housing (attached to the engine. It goes from the housing to the Idle Air Control valve. It then exits the Idle Air Control Valve and continues to the Throttle Body. It then exits the Throttle Body and goes to the thermostat housing. I found that this is CRITICAL for proper operation of the cooling system.
Here's how it works :
As the water in the engines starts to heat up, the warm water starts to flow through the 5/16" hose. It passes therought the Idle Air Control valve to warm the valve up as soon as possible. This will warm it up sooner than waiting for the entire engine to warm up. Doing this will give peak performance a few minutes sooner than if it were not designed this way, but once the engine has reached full, normal operating temperature, it does not do anything.
The warmed water exiting the Idle Air Control valve then passes throuth the Throttle Body and performs the same function (warm the throttle body sooner rather than later, again, not critical). These two things togther account for an increase of 3 horsepower during the warm-up period.
The warmed water then exits the throttle body and goes directly to the thermostat housing. Here is the critcal part. The point where the warmed water enters the thermostat housing is directly in line with the back side of the thermostat. Basically, the heated water "tinkles" (for lack of a better term) onto the back side of the thermostat causing it to open. It is designed such that if no heated water passes through this 5/16" hose, the thermostat will never open, resulting in hot water from the engine being re-circulated through the engine over and over until overheating occurs.
My diagnosis : The water is being blocked as it passes through the Idle Air Control Valve and /or Throttle Body preventing the water from "tinkling" onto the back of the thermostat.
My solutiuon : Replaced this "daisy chain" with a new, single 5/16" hose going directly from the upper radiator hose housing directly to the thermostat housing (thereby bypassing the Idle Air Control valve and Throttle Body). It takes less than 5 minutes to do it.
NEVER had the problem again.
Cost of repair : $1.79
well, all i can say is that for the first time, my fan is kick on when is about to over heat. i can see the temp. when up just a little bit. And then the fan kick on n it when back down.Thank BK in NH.