Internal vs External

[YukonJack]

My 47 Plymouth has the Thermostat housing without the bypass hose (mine is internal?) Is there any benefit to switching to the external bypass stat housing? Would it cause any problems to run it with both? If not, does anyone have the extra parts needed to change over? Thanks in advance.

[oldmopar]

There was is a change in head design sometime in the early 50's which is why the 2 different set ups since you have a 47 I would think it would be external but the engine or heads may have been changed over the years. Not really sure about switching thermostat housings I know you can use a internal water pump on both but a external is only to be used on heads with a external bypass hose.

[martybose]

It isn't just a change in the head, there's a corresponding change in the block as well. The later block (such as my D24 block) has an extra hole going into the waterpump that acts as the bypass path.

If your block is a P15 block, it won't have that extra passage. With the later housing on the older block, for all practical purposes you won't have any water circulation until the thermostat opens. Conversely, with an external bypass thermostat housing on a later model head and block, you would have two bypass paths, and might not get enough flow through the radiator to cool well enough.

Marty, been there, done that ........

PS, I'm pretty sure I've got an extra external bypass housing if you need one.

[Jim Saraceno]

I have a newer block, head and water pump. I also have an older, external bypass thermostat housing. In that housing I had the newer choke type thermostat. The engine has a tendency to run hot on hot days. I started thinking about the two paths of recirculation and decided I would put a stopper in the external bypass hose shutting off that path of circulation.

I did that in the fall and have not had any hot weather to see what difference it may make but so far is has run nice and cool.

I do think you need to match your thermostat with your thermostat housing.

[YukonJack]

It isn't just a change in the head, there's a corresponding change in the block as well. The later block (such as my D24 block) has an extra hole going into the waterpump that acts as the bypass path.

If your block is a P15 block, it won't have that extra passage. With the later housing on the older block, for all practical purposes you won't have any water circulation until the thermostat opens. Conversely, with an external bypass thermostat housing on a later model head and block, you would have two bypass paths, and might not get enough flow through the radiator to cool well enough.

Marty, been there, done that ........

PS, I'm pretty sure I've got an extra external bypass housing if you need one.

My 47 Deluxe has the original motor without the bypass t/stat housing. My housing looks like a later model V8. In pictures I've seen of other p15's and earlier, some have the bypass and some don't. I had a 48 Special Deluxe that had the bypass housing.

[greg g]

My early 46 had the non external thermostat housing. When I changed over to the engine from the 56, it had the same type system. Since that water pump was siezed I transfered all the stuff from the 46 over. So I don't know what influenced the selection of systems installed. Early, late, Deluxe. special Delux, it doesn't seem to be related. I actually like the internal by pass, the little piece of hose on the externals can be a piain in the butt.

[55 Fargo]

If that engine and block design was designed for an external by pass system, not sure how it will by-pass, with the internal t/stat housing and waterpump.

The internal type by-pass water pump can be used on an engine with external by-pass design, but the external by-pass waterpump usually can not be used on an internal by-pass system.

You say this engine is an original 47 engine, must be a P15 # on the block, could the head have been changed at some point. Does it work well like this, or have you had problems with circualtion till the engine warms enough to open the T/stat. In about the time this design was changed to an internal by-pass system,Chrysler also introduced pressurized cooling systems and rads, around 1951, these rads were fairly low-pressure with 4 lb rad caps........................Fred