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Username Post: Thermostat bypass passage - hooking up cooling lines        (Topic#174134)
apache31 
Contributor
Posts: 492
apache31
Loc: Northern California
Reg: 09-09-07
11-07-07 03:46 AM - Post#1290380    

Hi Guys,

Trying to hook up all of my coolant lines.

383ci with Vortec heads, Pro Products Crosswind Vortec Manifold, Stewart High Flow Water pump.

How do I know if my block has a thermostat bypass passage in it? This is a block casting #1024388

This is a fresh build so I do not have any pics or knowledge of how this is to be set-up.

The problem:
This manifold has 5 water ports in it. 4 of them (one in each corner) are 1/2 inch NPT and one (1) of them is a 3/8 inch NPT tapped hole facing forward toward the radiator just below the thermostat housing. Water pump has two ports; one on top and one on the side.

One reference I read stated:
"This manifold is primarily designed for
use on Vortec heads on pre-Vortec engine blocks. 1995 and earlier blocks have the thermostat bypass passage from the block directly to the water pump. Important: If you use this manifold on a 1996 and later Vortec engine (which doesn't have the bypass in the block), you must
run a coolant bypass line from the manifold to the 5/8" hose nipple on the passenger's side of the water pump. Route from 3/8NPT tapped hole in front of the manifold."

The ambiguity I am encountering is that when looking up my casting number on Mortec to see what year it is, it states it is from 1995-2000.

Referring back to the statement above, 1995 and earlier have the thermostat bypass in the block whereas 1996 and later do not. Going by my casting #, my block could be either.

How do I tell what I have?

Is that clear as mud??
"It was made to drive..."
1959 Chevrolet Apache 3100
My Truck Pics


 
black95jimmy 
"7th Year" Silver Supporting Member
Posts: 8693
black95jimmy
Age: 63
Loc: Venice, FL
Reg: 01-05-02
11-07-07 07:46 AM - Post#1290477    
    In response to apache31

Are running a heater?
82 Monte Carlo SC, 355 w/Vortec heads, roller rockers, 670 Street Avenger, Pypes true duals.
2000 Sub.5.3L 40 Gallons of gas @ $3.28/gal. bla bla bla.


 
Rick_L 
Honored Member
Posts: 25694

Loc: Katy, Tx, USA
Reg: 07-06-00
11-07-07 08:30 AM - Post#1290524    
    In response to apache31

The bypass passage on a small block runs from the water pump through the hole on the passenger side water pump mount surface just below the bottom bolt - to the passenger side cylinder head. The cylinder head has a matching hole.

So your block should have the hole below the bottom passenger side bolt hole.

But, it does not matter, your Vortec heads do not have the hole that matches the other end of that hole in the block - unless they have been modified, and I don't know if that's even possible.

You will need a thermostat with drilled holes in its periphery to have any bypass flow.

 
enigma57 
Senior Member
Posts: 9744
enigma57
Age: 66
Loc: Texas
Reg: 10-28-00
11-07-07 08:52 AM - Post#1290545    
    In response to apache31

Rich, late 1995 (early 1996 year model) through 2000 are the years that GM produced the L-31 Vortec truck engine. I believe that the instructions reference the hose nipple on the stock Vortec water pump for serpentine belt. However, you can plumb a tee fitting into the threaded outlet for the heater hose on earlier year water pumps as well. And if you have one of the very early short water pump castings having the extra tapped and plugged hole at 12 o'clock...... That hole can be used for the bypass nipple.

Follow the instructions regarding plumbing the tapped hole beneath the thermostat housing at the front of your Vortec intake manifold......

  • Quote:
...... Run a coolant bypass line from the manifold to the 5/8" hose nipple on the passenger's side of the water pump. Route from 3/8NPT tapped hole in front of the manifold.



Even if your block has the internal thermostat bypass passage corresponding to the cooling hole in earlier non-Vortec heads...... As Rick noted, your Vortec heads won't have a corresponding hole. And even if both your block and heads had this cooling passage...... Plumbing in an external thermostat bypass line certainly won't hurt anything. Go for it!

Happy Motoring,

Harry

 
apache31 
Contributor
Posts: 492
apache31
Loc: Northern California
Reg: 09-09-07
11-07-07 12:43 PM - Post#1290726    
    In response to black95jimmy

yes running a Heater and A/C
"It was made to drive..."
1959 Chevrolet Apache 3100
My Truck Pics


 
apache31 
Contributor
Posts: 492
apache31
Loc: Northern California
Reg: 09-09-07
11-07-07 12:51 PM - Post#1290734    
    In response to enigma57

Do I still need the thermostat with the drilled holes in it's periphery? Or does the 12 o'clock hole in the pump connected to the port in front of and below the thermostat housing on the manifold accomplish the same thing? The Stewart thermostat comes that way.

"It was made to drive..."
1959 Chevrolet Apache 3100
My Truck Pics


Edited by apache31 on 11-07-07 12:57 PM. Reason for edit: No reason given.

 
enigma57 
Senior Member
Posts: 9744
enigma57
Age: 66
Loc: Texas
Reg: 10-28-00
11-08-07 08:42 AM - Post#1291361    
    In response to apache31

Rich, utilizing the tapped hole at 12 o'clock (if your pump housing has one...... I believe that the Stewart pumps do)...... Will make for a cleaner installation of the bypass hose and leave the passenger side outlet for the heater hose nipple.

If you use the Robert Shaw thermostat as modified by Stewart......





...... The design is such that it would be hard to drill a series of 1/8" dia. holes around the periphery and probably unnecessary.

But if you use a Stant or other thermostat having sufficient material in this area......





...... It is a good idea to do so. (6) holes should be plenty. The holes allow any air entrapment below the thermostat to escape, minimizing the likelihood of steam pockets forming.

Hope this helps,

Harry

 
apache31 
Contributor
Posts: 492
apache31
Loc: Northern California
Reg: 09-09-07
11-08-07 11:07 PM - Post#1292056    
    In response to enigma57

Thank you Harry. I thought I read on the Stewart site that they do modify their stats with the holes or in some way that accomplished the same thing. I'll have to look at that again. Yes, here it is....

"Stewart further modifies its thermostat by machining three 3/16" bypass holes directly in the poppet valve, which allows some coolant to bypass the thermostat even when closed. This modification does result in the engine taking slightly longer to reach operating temperature in cold weather, but it allows the thermostat to function properly when using a high flow water pump at high engine RPM"

Thanks again Harry.

Rich
"It was made to drive..."
1959 Chevrolet Apache 3100
My Truck Pics


 
enigma57 
Senior Member
Posts: 9744
enigma57
Age: 66
Loc: Texas
Reg: 10-28-00
11-09-07 04:24 PM - Post#1292531    
    In response to apache31

That sounds about right, Rich. Got out my trusty old pocket calculator and (3) holes 3/16" in diameter have an aggregate area equal to the area of 6.75 holes 1/8" in diameter. So the Stewart thermostat should be fine.

Actually, I was looking at the Stant 'Superstats' with the intent of drilling (6) 1/8" holes around the periphery. After reading through Stewart's listings though, I may pick up one of their modified Robert Shaw thermostats and see how it performs.

Happy Motoring,

Harry

 
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