i dont like the coolant tank/radiator setup in the 400. should put a supra aluminum one in and a external trans cooler

 

The heat getting cool at stop lights is a dead give away that the system has air in it. I read on here somewhere that these systems are self purging. Take off the radiator cap and make sure the radiator is full up to the neck, replace the cap and then add coolant to the overflow tank up to the full hot level. Go for a drive, I'd say drive for 15 or 20 minutes then pull over and check the level in the over flow tank (do not remove the radiator cap, you'll regret it) if the level in the over flow is low or its empty add more coolant and drive more. You may heave to repeat this refill and drive step a few times, but when you add coolant and drive and at the next level check you see there is sill coolant in the over flow tank your almost done. Fill the tank back up to the full hot level and your done.

 

maybe the setup is wierd on the 400, but I check the radiator on the 300 for level not the reservoir really. can you check for fluid in the radiator?

 

Problem solved...as many of you guys said, it was a massive air bubble in the system. I didn't actually have a coolant leak but more of a coolant blow back from the build up of pressure in the system due to the air bubble. This basically happened because of the timing belt/ water pump change. Apparently not everything was put back exactly like it should (coolant resevior, radiator)...I pick it up in the morning.

 

My STS is like that, I guess they figure if the only access to the system is the overflow tank you'll keep it full and its easier to purge.

 

soo how do you purge the system?

 

Follow the procedure I outlined in post #17.

 

Coolant leak at steering box is coolant being pushed out the expansion tank as it is over filled and laying sideways allowing the cap to be submerged. Thus, pushing out fluid instead of vapor.
To correct this, we removed the excess fluid from the expansion tank and repositioned it to its proper location. It was a bit difficult as the radiator did not exactly match the tank(aftermarket radiator) Then, for the over heating and lack of coolant, this problem was due to fluid not getting in to the engine from the expansion tank. There is a big plug that must be removed to fill the engine block up correctly and remove air from the block. Doing this, we added one gallon to the block.

 

I'm having the same problem right now in 50 degree weather in vegas. I had one shop tell me it si hg but from what I've read from everyone I'm gonna start at the heater control valve. Coolant is coming out too fast to be HG and no coolant or smoke is coming from my tail pipe. I think we've both got a heater core problem. Also my LCD indicator is half fogged up.

 

Have them pressure test the coolant system...read all the other repsonses here and then read my last post with the fix to the problem. Good luck!