Intake Manifold

Also, I've read that the thermostats are necessary for the engine to operate at the correct temperature and it's not a good idea to remove them. I will probably leave the system as designed. There seems to be no compelling reason to change it.

Pat, I wasn't concerned about putting a hole in the thermostat. I was concerned if it would provide enough water to the water pump when they are closed. Normally the water is supplied through the intake manifold so if that was blocked off, would the holes be enough to compensate.

If you are concerned about the the hole in the thermostat, leave them out. That what we do on all our Cords and they run cool.

Pat Leahy

Scott,
If you are concerned pressure test the intake manifold at 5 psi. I use a piece of inner tube and hose clamp to block the openings and a set screw in the drain hole. Pump it up to 5 psi and place the intake in a tub of water and see if you have any air bubbles coming out. You will need to rotate it to get the air out of the passages and to see if you have any leaks. The leaks are most likely to be on the bottom surface or in the passages.

If the manifold passes the test then it's OK to run water thru it.

When you install the intake and exhaust manifolds use the one piece gasket and make sure you chris-cross your tightening (same as on the heads) of the nuts to pull both sides down evenly. 

Jim
 

Gary and Jim,
Thank you for your responses. My concerns are:  1. Even with a hole drilled in the thermostat, I was concerned about having enough water returning to the water pump. 2. The engine was just rebuilt, I am hesitant to drill the block at this time.  The short block is finished, I am completing the rest of the assembly.
The hose nipples on the intake are somewhat corroded so there is a concern for leaks. I might be able to get them to seal if I don't block them, it didn't leak before I took it apart. Just trying to decide which way to go and wanted to check on the current thinking on this.  Thanks again,  Scott

 

Hi HDVETTE,
You can block off the water flow thru the intake manifold. I think this is going to become more common as time goes on as the intake manifolds are starting to rot out and are dumping water either into the crankcase or into the cylinders. I have seen or heard of three in the last few years doing this.

The cooling system design allows water flow from the block thru the intake manifold to the water pump during warm up. This bypasses the radiator during warm up and allows the intake manifold to warm up quicker. This is useful during cold weather operations. Once the engine warms up, the thermostats open up closing off water flow thru the intake manifold and opens flow to the radiator thru the upper radiator inlet tubes.

The down side of blocking off the water flow thru the intake manifold is there is no water flow until the thermostats open up. If you drill a 1/4" hole (step 2 below) that would allow venting when filling the system and also allow a small flow thru the system during warm up without delaying the warm up. You can pick the size of the hole you think will work best.

To block off the intake manifold you need to:
   1. Plug the outlet of the thermostat housing. This can be done by plugging the thermostat housing or the inlet on the intake manifold. I have done it by taping the two inlets to the intake and putting in a plug (I don't remember what size I used). Make sure it seals tight.
   2. Drill a small hole in the thermostats to allow them to vent.
   3. Plug the outlet of the intake manifold (to the water pump). This can be done the same way as the inlets or you can put a plug in the hose and use a hose clamp to hold it in place. 
    4. Lastly plug the drain hole in the block. Drill and tap and install a set screw with Loctite. Make sure you do this in the block and not in the intake. This way there is no chance of leaks.
 

The idea behind not allowing coolant to flow thru the intake has many reasons. But the most important reason is the aluminum casting was not the very best compared to the alloys today. In the recent past a member posted about a hole he found in his underside that would allow coolant to flow into the oil pan eventually ruining the engine. Our cooling systems are zero pressure. So using most any form of plug stops the flow of coolant into the intake. Even RTV can make a great plug. Another reason is heating up the underside of the carburetor can cause what was called vapor lock. Then the engine won't start after city or freeway running. Others will add to these reasons. I know the Duesenberg engines from a restoration shop near me has for years no longer allow coolant to flow thru the intake manifold because some were found to have rotted out.


Gary Parsons

What are the current opinions on bypassing the water flow through the Intake Manifold?  I have read advice to plug the passages in the intake but not sure how to do it or what effect it has with regard to the hole into the block and the connection to the water pump. Any suggestions, comments, instructions, or theories appreciated.