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LS Tech and Moderator
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Discussion Starter · #1 ·
Repost of the info I saved from the lost thread.

The "steam lines" are more to help air get out of the top heads. Typically they will be full of coolant when working right. The line will run from the front of the head through the throttle body to either the top of radiator or the expansion tank. Depending on application. Also, the Trailblazer V8/TBSS actually runs it into the heater hose at a point higher than the head outlet. As the radiator was setup for the I6 motor and that was the easiest/cheapest way for GM to make it work when they added the V8's vs making a all new rad to simply add the steam bung. Now they ran through the TB to prevent TB icing at or near idle since the motors are designed for use over a very wide operational environmental range. The TB coolant line can be bypassed to reduce TB temp and improve performance.

Now Charlie is right, there is much debate. Is it needed or not? I would run it. One it helps bleed air on initial coolant fill. Second it helps prevent air pockets. Now some people have blocked it on their motors have ran fine no issues.

Also if you notice some of the early truck motors had all four head ports (two at back of motor and two atthe front) plumbed to the front side discharge point. Two at the back moved under the intake to the front lines with an outlet to the TB just like the car motors have. The later truck motors after 2000 or so deleted the rear lines and added plugs. So only the front two ports have the lines. So I guess GM figured a full four port system wasn't needed.

Either way its easy typically to hook up. Some have ported it into the top of the water pump outlet. Ideally you want it at a point at or near the top of the radiator itself as they typically set higher than the motor to get all the air out.

Fixed the title for you odass150 and will add this to the LS FAQ sticky as well.
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