Between the distributor lock down bolt and the EGR tube fitting on the intake manifold there is a fitting with a steel tube with a rubber hose connected to it (the fitting is right next to the dist. lock down bolt). When I bought this motor alot of stuff was tagged and labeled, but not this fitting/tube. Can anyone tell me what it is for and where it connects to ? Or if it is needed at all ?

Thanks

 

Delete
Is a bleed line to vent steam from rear of heads that ran to one of the heater hoses.
Mine has been gone for 10 years with no problem.
FWIW , only the factory intakes have it

 

thanks ! now it makes perfect sense.. it looks to me like some sort of mini water hose, even a little rusty like you would expect, there must have been a small "T" or something to tap it into the hearter hose.

what do you do with yours ? just leave it open to the air or run some sort of vent hose down and under the block, sort of like a radiator expansion tank vent hose ?

 

Has to be sealed off ( or connected to rest of coolant system )
otherwise you will loose all your coolant

Remove the complete fitting from the intake and install a pipe plug.
IIRC 1/8" NPT

 

There's no steam or if there is the coolant is boiling.

The Vette L98 restricts the rear intake coolant passageways to keep coolant at the rear of the heads longer. To provide a sufficient supply of coolant, a bypass hose is teed into the heater hose and runs to the rear of the intake. If you remove it, there's a good chance you'll burn up the rear pistons unless you use intake gaskets without the restrictors - which is how the F-Body L98 is set up (Note - '91 and current production 113 heads require a special intake gasket still. Those heads are counterbored for gasket retainers to keep the gaskets aligned when you install the intake. You can get them with and without the coolant restrictors, though the Vette gaskets (with restrictors) is difficult to find since it was only used on the '91.
Read all about TPI's here: http://www.hotrodlane.cc/PDFFILES/TPIStory.pdf
You can also poke around the site for videos and other how-to's. If you need parts, call them; friendly people.

 

Thanks very much. Pretty cheap insurance and peace of mind to "T" the by-pass hose into the heater hose ....

 

My Tpis intake has it.
I had thoughts of eliminating the hose 'till my mechanic said to LEAVE IT THERE.

To SunCr, thanks for that link. New to me and interesting.

 

absolutely leave it !

That water (coolant) that exits that little hose is the hottest water in the system because its carrying the heat from the rear cylinders. Its small to keep tension on the system and help keep the passages full so they do NOT turn to steam and have hot spots. That rear intake area also gets hotter from the EGR port being right next to the water passage...not a coincidence. EGR gas can be several hundred degrees and cause need for cooling for the intake.

Since the front exits are larger and water free flows out there, the rear needed to be orificed with the small hose. The front of the intake also has a small orifice to keep water backed up to make sure the top end stays full.

 

Thanks. I am running the motor in an offroad racer so "normal" overheating is definitely a potential issue and for this I have replaced a standard heater core with an auxillary radiator tucked away above the rear axle. I dont need to make the overheat problem bigger by messing with this cooling feature of the motor. Kind of reinforces the belief that the Chevy small block is about as well designed as any motor ever was and its tough to improve on the basic design. I'm hoping the "T" to tap into the heater hose is a dealer item so I dont have to make one out of copper tubing ....

 

So how come there are no reports on here of guys burning up engines when running popular L98 aftermarket intakes with no rear crossover (MR ,HSR ) on 113 heads ?
The ZZ4 crate engine which uses the same 113 heads doesn't have a crossover on the factory supplied intake either.

I suspect like the heating on the TB it was a "worst case" provision by GM engineering?

So why is this provision only necessary on 113 heads and no other aftermarket Alum heads?

Which is only a big bore version of the stock intake

 

I wondered the same thing... but figure maybe its because the after market intakes and the gasket used do not cause the restricted flow ? But that's a guess because I dont know. Anyway, since the fitting and tube are there on my motor its a simple thing to plumb it into the cooling system if only just for peace of mind.

 

When I swapped over to a superram intake and base, i couldnt find that steel hose which bolts to the intake. My intake base already had a plug in it, so I plugged the rubber hose and clamped it, no issues in 3000 miles

When i take my intake off next time, I plan on hooking it back up, just because I do not like having the hose tucked away near the blower motor box.

Mike

Mike

 

The motor I am replacing in my racer with the L98 is a stroked in-line jeep 6 cyl with an alum head,it is nearly 5 liters with the stroke kit. It always had overheating issues, thats why I put in the aux radiator. Whether or not the L98 will run hot or risk damage to the rear pistons w/o the vent tube is a guess Id rather not take. and by the way, compared to some jeep forums I used to visit this forum is great for offering help .. for some reason the jeep forums seemed to want to make people asking for help feel stupid for even asking ... or just give sarcastic answers. you guys have a good thing going.

 

thanks for the article from hotrodlane.. very informative. the picture on the cover reminds me of the last 6 weekends Ive spent with my boy getting the L98 ready to go ..... . especially the look on their faces like - "ok, now whats this... "

 

The aftermarket intakes have no flow at all because of lack of rear crossover
Coolant from rear of heads can only travel to the front as with every other GenI SBC (ex alum L98 )

 

I have wondered at times how important that steel steam pipe is on my L98 1987 Vert too.

Hasn't rusted out so I left mine intact.

Keep the coolant mix changed every couple of years & clean.

 

this forum is like an encyclopedia ...

 

Just don't expect everyone to agree .

 

then it wouldnt be a forum .... all opinions and advice welcome. its up to the asker to figure it out from there. like i mentioned, compared to some other "forums" about motors and tech advice, this one is really good and its plain the members are trying to help. even with me as a newbie starting this thread, there has been lots of interest and advice from veterans...

 

Again, this design is only on the Vette L98. Vette's have always been a Beta for whatever GM wants or wanted to try on everything else - sometimes with poor results, but a loyal following has kept the car alive when others would have failed.

TB heating is there because electronic fuel injection cannot work (or the engineers didn't think it would work very well) if it started from an unknown. They calculated a set point from which all the other variables worked. Believe it or not, intial idle setting is for one temperature and one air flow at one humidity. From there, everything else does ok. That's science and math. If you can come up with something different, you'd probably win a Nobel Prize.

Problems? My guess has been that the restricted, rear coolant passageways, is why there are so many blown head gaskets on the 113 Vettes which universally fail at cylinder 7, quite a few right around the expiration of the initial warranty (but there are still a ton around here). GM's analysis was leaking intake gaskets set up galvanic corrosion which then ate up the head gasket. I think that's only part of the story. The other part is the restiction simply keeps the toxic mix at the rear of the head longer so it eats it up there first. Their Bulletin and redesigned was to stop the intake leaks and maybe because it only had to serve for one Year ('91), they didn't need to eliminate this feature which was exclusive to the Vette. ZZ4's don't have it, but they have the redesigned 113 head to eliminate the initial problem which is misalignment of the intake gasket. GM has pretty much eliminated coolant flow through the Intake on anything the make now as they could never figure out how to screw one together that doesn't leak (again, that's my guess).

For someone who posted something about a restriction at the front of the Intake - there isn't one, but the Factory Service Manual shows that you install the gaskets with the restriction up front. That's wrong and was corrected by yet another Service Bulletin.

I think someone else posted that the bypass is outflow from the heads/manifold? It's the other way around; ie, it's extra supply for whatever is going on back there.