changing thermostat housing - anything else

[Lou Earle]

I am working on an A/C-alternator plate bracket set up and Have found it will probably be easier to do if I can use the 54 thermostat housing(low profile type) rather than the older version. If I put the 54 housing on the 48 engine are there any other changes that need to be done?

Lou

[Lou Earle]

Please explain- I am not aquainted with that- do I need to change water pumps?

[Normspeed]

This subject somehow makes my brain hurt. Maybe Don C will chime in.

[grey beard]

Early - like 48 and 49 - models all originally used an external bypass route for the coolant. This bypass is visible on the outside front end of the thermostat housing and is exhibited by a very short length of heater hose between the housing and the stem that mounts on the water pump, from which a heater hose connection is typically sourced.

This is not rocket science, and can be easily understood with two minutes of visual inspection. Later models used an internal bypass system which was visible only by a small bump on the very front of the cylinder head, above the water pump and a little to the passangers' side of the engine.

The point of all this wordage is this: You must have some sort of bypass. You can have both and there is no problem. Just don't mix and match parts and wind up with none.

(The bypass circuit is used only when the engine is cold and the thermostat is closed. It limits coolant flow to the block area only and not to the radiator to expedite warm-up time.)

[Don Coatney]

I have been beat up so many times when I discuss my thoughts on this subject that I am gun shy.

However any by-pass system (internal or external) exists to allow water to circulate in the

block and limits coolant return to the radiator when the engine is cold and thermostat is

closed. An external by-pass system is easy to spot as there is a short external hose

running from the thermostat housing to the suction side of the water pump where the cabin

heater return hose connects as pictured below. With an external by-pass system the water

follows the route of the pipe cleaner pictured below when the thermostat is closed.

There are two types of internal by-pass systems. One has the bump on the head as has been

mentioned and the other does not. Both of the internal by-pass systems do not use the short

hose between the thermostat housing and suction side of the water pump. I believe there is a

different backing plate on the water pump of an internal by-pass system allowing flow back

to the water pump. Hopefully those who are in the "know" will chime in with correct information

on this.

It is my belief and not proven that if an internal by-pass thermostat housing is used without

internal provisions in the engine block and backing plate on the water pump to allow water to

return to the water pump that there potentially could be a build up of pressure in the

water jacket of the engine. The water pump is not a positive pump and will only build

pressure until the pressure exceeds the clearance between the pump rotor and pump

housing at which time slippage will occur. However that pressure combined with thermal

expansion of the heated coolant potentially could build enough pressure to cause leakage

or blow out of an expansion plug. Some will say I am all wet with my theory but that is my

story and I am sticking to it until someone can prove me wrong.

[Normspeed]

Don, if Lou went to the later therm housing without the bypass hose, would his earlier engine block have correct openings to match up with an internal bypass water pump setup? That's where I get confused.

[Normspeed]

So it sounds like the answer to Lou's question would be, don't use the later model therm housing on the earlier block...?

The reason I ask is, 47Heaven has something similar and he noted his engine seems to run a little warm and has also popped out a couple of expansion plugs.

I believe he's running an earlier Dodge 230 block, late model therm housing. Not sure which head.

[Lou Earle]

I took a look at my 48 and then 54 engine and sure 'nough the heads are different - I had never noticed that before. What if you used the later style thermostat and drilled some holes in it to let some water pass thru as the engine warms. That is use the new type neck and thermostat on old head and then drill the flange on the thermostat to allow some water flow . I wonder if that will work?

Lou

[martybose]

No, because the rest of the water path for the internal bypass is a moon-shaped cutout at the top front of the block that lines up (through a gasket) to a similar hole in the later water pump.

Marty

[Normspeed]

Just thinking out loud here, but if you had the older block and wanted to run internal bypass, how about drilling a 1/2" hole in the correct spot on the front of the block? Shouldn't be too hard to drill through cast iron. The gasket would tell you exactly where to drill.

No, because the rest of the water path for the internal bypass is a moon-shaped cutout at the top front of the block that lines up (through a gasket) to a similar hole in the later water pump.

Marty

[martybose]

Just thinking out loud here, but if you had the older block and wanted to run internal bypass, how about drilling a 1/2" hole in the correct spot on the front of the block? Shouldn't be too hard to drill through cast iron. The gasket would tell you exactly where to drill.

It sounds right, but I can't remember if my old block had a machined surface there that a gasket would seal against. If it does, it will work.

Marty

[james curl]

The boss stands proud on the block. On a external bypass engine the head will only cover half of the boss. On the internal bypass system both the head and the block have a boss cast in them for the water passage. I use the new style head gasket because that is what is available and in the front of the engine on the passenger side of the block you can see the gasket with half a hole showing sticking out in space in front of the engine.

[James_Douglas]

Take a look here to see the holes in the pump plate, the early ones with the external bypass must be welded up:

http://www.dacoglu.com/cooling.htm

If you look here, you can see what I made to replace the stock water neck so I could use a SBC thermo and have my choice of temperatures.

http://www.dacoglu.com/newengine.htm

James

[blueskies]

Here's a couple of pictures for comparision. If the pictures do not show, hit refresh on your browser...

My engine is a late production '50. It still uses the external bypass thermostat housing.

This picture is from way back when I pulled the head for the first time. Apparently it had been given a new headgasket at some point, as you can see the internal bypass spot on the surface of the block from the hole in the late model gasket.

Also, note that the face of the block extends beyond the head and gasket surface a bit, to where the water pump mounts on the front of the block. I don't think that the milled surface on the block extends quite far enough to reach the outside part of the hole, but the block itself does.

Here's a picture of my original 1950 external bypass head, and you can see the same rusty spot on the edge of the head left by the late model internal bypass head gasket.

I have not see an internal bypass type head, to see if it has a boss on the front face of the head to allow for the bypass hole to align with the block and gasket, but it must have the boss or be longer toward the front of the block to accomodate the hole.

I'm running an EDGY head on my engine, and it comes with a boss for the bypass hole, but is not drilled. The heads come this way from EDGY so that they can be used on either engine. The hole has to be drilled for use on the internal bypass type engine block.

Here's a picture of the head sitting on the engine. You can see that the head is not the same overall length as the block, and you can also see the boss on the end of the head that covers the hole in the gasket.

Here's a picture of the edgy head from the bottom. You can see the boss on the edge of the head on the left.

I don't think you can simply drill the holes to make the early blocks and heads work as an internal bypass system, because the early heads don't have the boss, and the early block's gasket surface doesn't extend quite far enough to reach the outside of the bypass hole. At least not on my 1950 engine...

Pete