I am troubleshooting the cooling system on a 1987 Merc 200hp. My question: there is a hose coming from the thermostats and this goes to a tee fitting. One end of the tee goes to the telltale and the other appears to go back into the exhaust manifold (I have disconnected it momentarily and exhaust gas comes out but no water). What is the purpose of this? The reason I ask is that I have a lot of water vapor coming out of the exhaust (a sign to me that the motor is overheating). At this point I have a new water pump in it and new thermostats and I plan to pull the heads this week to check the water passages. Any ideas appreciated. Thanks.
