Steam Vent Tubes, how to deal with them?

Thanks to a recent Roadkill Garage episode, I realize I need to do something about these for my LS4.9 cylinder head.
The original reason they exist is because the thermostat is lower than than the coolant level in LS engines, I'm planning on cutting a nice little hole in the end of the cylinder head for the thermostat, so I shouldn't have this problem, right?

If I don't have this problem, is there any reason I shouldn't just get some of the existing vent tubes and seal each one?  I'd prefer not to do a permanent change to the head until I have to (says the man that cut up two heads and made one)

Vent tube, if you don't know what I'm talking about.
My cylinder head

Random bling bling pic I found online

Not so much that the thermostat was lower than the coolant level, but that the water outlet (down in the deck) was lower than the highest point of the water jacket.  The thing with those bleeds is that they were the highest point of the water jacket, when the head was 45 degrees from vertical.  You're making the head horizontal, so those bleeds aren't going to do much of anything anymore.

If you're going to stick a thermostat on the end, you'll probably be okay.    A pathologically correct Fix would be to find the highest point of the water jacket and make the bleed there.  (Or just shade your thermostat as high as it can go, and maybe drill a 1/8" bleed hole near its edge and clock it at 12 o'clock)

(edited  because I had an epiphany, and then edited again to reorder the sentences for better thought-flow)

If you are unsure what you want to do,  you may be able to get OEM block off plates until you decide if you need to have a vent.  My 2001 LQ4 has the rear steam vents blocked from the factory, I think.

Lots have the rears blocked from the factory with little bolt on plugs

Patrick (Forum Supporter) said:

Lots have the rears blocked from the factory with little bolt on plugs

So, that Camaro that I LS swapped.  I got the engine in the car and running, after way WAY more effort than it should be to put an F-body LS1 in a 4th gen F-body, and found it had a massive oil leak coming from somewhere on the back of the engine.

Turns out, the machinist who assembled the engine was a Perfectionist, and didn't believe in using those bolt on plugs when he could simplify everything and just TIG the coolant holes shut.  Which was great, except the bolts that hold down the plugs/vents go through to the crankcase area.  No bolts means large oil leak as windage blows oil up and out.

Patrick (Forum Supporter) said:

Lots have the rears blocked from the factory with little bolt on plugs

Thats good to know.  Add to my list of things I need to scrounge from somewhere. 

Pete. (l33t FS) said:

Not so much that the thermostat was lower than the coolant level, but that the water outlet (down in the deck) was lower than the highest point of the water jacket.  The thing with those bleeds is that they were the highest point of the water jacket, when the head was 45 degrees from vertical.  You're making the head horizontal, so those bleeds aren't going to do much of anything anymore.

 

If you're going to stick a thermostat on the end, you'll probably be okay.    A pathologically correct Fix would be to find the highest point of the water jacket and make the bleed there.  (Or just shade your thermostat as high as it can go, and maybe drill a 1/8" bleed hole near its edge and clock it at 12 o'clock)

 

(edited  because I had an epiphany, and then edited again to reorder the sentences for better thought-flow)

I still have the leftover pieces of the cylinder heads.  Exploratory surgery may be required 

Since I own an LS, too, where do those vent tubes vent to?

In reply to DeadSkunk (Warren) :

They vent to either the radiator or the expansion tank, after first passing through the throttle body.

In reply to DeadSkunk (Warren) :

From my (limited) knowledge, they dump back into the coolant system somewhere.   Should be able to follow them to what hose they hook up to if its in a car already?

Pete. (l33t FS) said:

In reply to DeadSkunk (Warren) :

They vent to either the radiator or the expansion tank, after first passing through the throttle body.

Didn't they eventually stop running them through the throttle body?  I think I read that as I was looking into throttle bodies

DeadSkunk (Warren) said:

Since I own an LS, too, where do those vent tubes vent to?

Cold side radiator end tank.

In reply to Mr_Asa :

Now that you mention it, I think they did.  I guess throttle icing isn't as much of a problem as it used to be, or as they thought it was.

Mr_Asa said:

Didn't they eventually stop running them through the throttle body?  I think I read that as I was looking into throttle bodies

Yes, around the Gen III -> Gen IV transition, I believe. LS1 had it, LS2 didn't.

obsolete said:

DeadSkunk (Warren) said:

Since I own an LS, too, where do those vent tubes vent to?

Cold side radiator end tank.

Hmmmm, so I need an appropriate connection point on the Mustang radiator in my Corolla...

Easy button would be to tap those coolant holes to 1/4" NPT and thread in either plugs or radiator petcocks like this

The petcocks would give you handy bleed ports on the top of your motor

Trent said:

Easy button would be to tap those coolant holes to 1/4" NPT and thread in either plugs or radiator petcocks like this

The petcocks would give you handy bleed ports on the top of your motor

The pic of my engine in the original post is how it will be mounted, so it'll be nowhere near the high point of the engine/coolant system so it won't work as a bleed port.

The 90's LT1 had them too. On the swap I did, I found a heater hose tee with a small branch that I hooked the steam lines to. Best to hook them on the cold side/returning to water pump.

DeadSkunk (Warren) said:

obsolete said:

DeadSkunk (Warren) said:

Since I own an LS, too, where do those vent tubes vent to?

Cold side radiator end tank.

Hmmmm, so I need an appropriate connection point on the Mustang radiator in my Corolla...

In my LS swap, I've added a coupler with a 1/4" NPT fitting to the upper radiator hose, which was convenient, since I needed some couplers anyway to custom make a hose that will fit.  There's a picture here in my build thread.

In reply to 81cpcamaro :

Best is to the highest point of the cooling system, so air actually travels up and out.

This is why they were routed to the hot side of the radiator, or the expansion tank.  Highest point for whatever particular chassis.

I'm working on an LS swap right now that had the two rear ports capped off from the factory. Due to various nuances of my swap I wanted to use a  full four port steam setup. So I used a nice aftermarket kit.

Common method is to tap a fitting into the top of the water pump and tie the steam manifold into there. But it's just not sitting right with me.  GM never did it that way. Yes, a bunch of swappers have had success running it into the pump. I'm still waffling about it but I'm leaning towards going to the upper radiator hose even though it will clutter up the look of the end result. I'm convinced that GM engineers are smarter than me and would have run it to the water pump since it's so much easier if it were a viable option.

In reply to Cousin_Eddie (Forum Supporter) and Mr_Asa:

Will the radiator and expansion tank from the donor fit in your truck?  If so, you could just replicate what GM did exactly.  I just checked the tank, and it looks like the steam vent tube connects above the fill line, which I guess make sense, since the whole system is pressurized at that point.  There's not enough room for the tank in my project, or I'd consider using it. 

Another option for a general swap project could be grabbing an expansion tank from a newer GM car, and running a custom fit radiator without a cap.  I'm passing on this option because I already have a perfectly good, lightly used radiator in mine.

The early LS1s hads a 4 port setup from the factory they are getting a little hard to find and people wanted good money for them last I looked. Shortly after GM started blocking the rears. This was pretty common for people to do even on cars that came with a 4 port setup, they did it  for manifold clearance normally.

It is also quite common to just block all 4 on modified cars. There is quite a lot of argument about how useful they actually are but I know more than handful of people that have blocked them all on highly modified cars that have had no problems. I ran a 2 port setup IIRC.

As explained to me the purpose was the head is the most likely place for the coolant to boil, gas doesnt transfer heat as well as coolant/water so if coolant boils and cant escape you get a hotspot in the head, so they give the potential gas a place to exit, normally some high on the cooling circuit like the top of the radiator or expansion tank.

I think the easy solution would be to block rear and run a single port on the front of the head to the top of the radiator or expansion tank, but with a longer head it could be more important to have the rear functioning also. Either way you can take one or two delete plugs, drill and tap them, add  a fitting and run a hose over or under (if you can keep it from dropping substantially) the intake runners where it Ts to the front port and continues on to the rad/expansion tank or just one hose if you plug the rear.

In reply to eastsideTim :

You gotta check the link in my first post, my man.  Im not installing a LS series engine in my truck, I'm installing a fairly highly modified head on my engine.

The steam vent no longer does what it did on the LS engine, so installing steam tubes is a non-starter. 

In reply to Mr_Asa :

For some reason I was thinking you were likely going to have the thermostat too low also.  If not, then I'd be inclined to just block off both vents.