Crossover coolant tube(Not sure what to call it)

[softballnrd27]

What is the purpose of the crossover tube that bolts to the heads up front? I know it can be hooked up to your TB to help warm it up faster. Is there another use for it? Can I just put the little blocks like on the rear of the engine?

[68Stepbed]

Those are steam vents. They are to keep from getting steam pockets built up inside the heads. As for using them to warm up the throttle body, that's what GM uses them for. All factory lines have an outlet to go into the throttle body. They also connect into the coolant system to help bleed out the excess steam.

[Shon]

most will bypass the TB though. and some aftermarket TBs do not have this provision.

[nomrlz]

blockin that off is the first thing most gearheads do

[gringoloco]

Just for clarification, blocking the ports completely is not normally suggested, bypassing the throttle body is common.
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[nomrlz]

^^^ this. i shoulda clarified i meant TB bypass

[68Stepbed]

I ordered some of these to build my own custom plumbing.
http://s41657.storefront-solutions.c...l.aspx?ID=3289

[mooseknuckles]

heres what I did....drilled and tapped for a 1/8"npt in the back of the water neck...bought a 90* and a 1/4 barb fitting....connect with a hose to steam lines bypassing throttle body.....not the "correct" place to tap into, but I wanted it "out of sight", and it looks 100x better than a hose running all the way to the radiator.....

[68GMCCustom]

that should work out great.

[mooseknuckles]

yeah....hope so, not very noticeable either...

[softballnrd27]

OK. I have moments where I feel totally lost on such simple stuff.
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[68Stepbed]

Don't worry it happens to all of us at times.

[gringoloco]

My understanding of the coolant crossover and steam port is that it is designed to relieve hot spots from stagnant coolant or steam pockets that collect in the cylinder heads. They collect here because it it the highest coolant passage in the engine. This was not a problem on traditional SBC due to the coolant crossover in the intake with the upper hose attached. The reason we can cap the rear ports is due to the installed angle of the driveline, which forces the air pockets to float to the front of the engine.

Knowing that heat rises and air floats, I don't see how the common practice of tapping the water pump solves the issue. Wouldn't we want to place the steam line in a place higher than the cylinder heads?
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[68Stepbed]

It allows the steam to flow back into the system and the vapor bleeds back through the overflow vents. The line needs to be connected into the return part of the system so it pulls the steam vapors back into the cooling system.

At least, this is my understanding of how it works.

[68GMCCustom]

the crossover tube on our LS2 powered TrailBlazer SS connects to one of the heater hoses....well below the height of the crossover tube, around exhaust port height or lower. My guess is its the "to" line for the heater and puts a suction on the crossover tube.

[RR440MAN]

OK, I have been delving into this steam port issue on a 2006 6.0 LQ9 swap into a 71 GMC. I would like to utilize the rear steam ports. The dilemma is it is hard to justify spending 140-$200 bucks on a steam vent kit. I want to utilize the TB coolant line due to possible cold weather application. Since I have the engine on a stand and have been freshing up the engine heads, lifters, I had removed the front steam crossover tube. To check I placed the crossover tube at the rear of the engine by reversing it and it seems it would fit properly with the TB tube being on the other side of the rear of the engine.

So my question is : If I get another front Oem crossover tube, some rubber hose ; a tee which would tie in the front and rear crossover tube and route to the TB coolant line a viable cheap alternative? Of course I would route the output back to the radiator inlet. Any thoughts on this on making it work effectively? I think it would benefit to use both front and rear since engines and terrain dictate angles of the engine instead of relying only on the front ports.

[ls1nova71]

I see what you're getting at, but using all 4 really isnt necessary or GM would have kept using them like they did in the earlier years of LS engines. What you are thinking of doing could work, but you are going to have a place for potential leaks, however unlikely, just throwing it out there so you are aware. If you are dead set on using all of them, then just get a steam tube set up off a 99-00 engine since it's all one piece. They are really easy to find in the pick n pull yards since everyone is looking for the newest engine possible the older ones get left behind.

[dec010974]

@RR440MAN, Ls1Nova71 is right in reference to the steam line scenario. I never crossed over all 4 steam lines for any of my LSx swaps. its over kill. In your case, we gotta let "Jessie rob the train." But in LS1 performance, they used the crossover tubes to all 4 corners, (something about #7 cylinder). Good luck with your build, Clark.

[homemade87]

I think the 4 corner was made to accommodate engines sitting at near zero degrees like the corvette . 4 corner vent would be a must in this situation . The rear could develop an air pocket and create a hot spot . Also a must in a swap sitting close to zero degrees as well . Most swaps are at least 3 degrees or more and would not necessarily need the 4 corner . The air would migrate to the front steam vents anyway . Thats why everyone says never had a problem with just the front vents only ( including me ) . It is doing what its supposed to at those engine angles .

Add it if you must , but if the engine angle is a 3 degrees or more it will not be necessary .