JamesLay

31-32 plymouth water pumpII

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I have 2  PA water pumps ,could some one explain to me why they have different holes in the backing plate.and witch backing plate would be the best to use. pumps are identical except for bypass (D shaped hole). the one with out the D shaped hole was on a PB motor the other came off a PA motor. the holes in both blocks are identical.

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Plymouth Master Parts list  gives all the same numbers for PA and PB water pump.

Also same number for water pump cover plate if that's what it is.   I have a couple of water pumps that are not on the car.  I will see if they are different

May be a few days before I get to my garage.

Could that D hole be just a corroded hole?

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no, i have seen the D shaped hole on one for sale on ebay in the past. these are not my water pumps. my backing plate is not very rusty and the hole is very defined. also if you look at the 1933 plymouth water pump it has the D shaped hole. I'am  thinking if to much water bypasses not enough is going to the radiator to cool ,there for the pump with out the D shaped hole would be sending more water to the radiator. i saw those part numbers like you stated are the same. i dont get it thats why i made this post.  i would like to know what backing plate to run. i gess i could try both and see witch one runs cooler.

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Hello,  Please note that a 33 Plymouth did not have a by pass.  It was added in 34.

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Hi, i have both pumps on the bench now so i am going to run the  the by pass  backing plate . i had the one with out bypass on the car and drove it 400 miles last summer. on the real hot days the temp gauge would creep up when sitting still. and it seemed to  float around between 160 and 180 degrees it has a160 thermostat.i have heard the term " HOT SPOTS" if you dont have bypass. the six cylinder water pumps claim it fit from like 34-54 and i notice they have external bypass nipple port.

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On 3/24/2020 at 5:52 PM, JamesLay said:

no, i have seen the D shaped hole on one for sale on ebay in the past. these are not my water pumps. my backing plate is not very rusty and the hole is very defined. also if you look at the 1933 plymouth water pump it has the D shaped hole. I'am  thinking if to much water bypasses not enough is going to the radiator to cool ,there for the pump with out the D shaped hole would be sending more water to the radiator. i saw those part numbers like you stated are the same. i dont get it thats why i made this post.  i would like to know what backing plate to run. i gess i could try both and see witch one runs cooler.

 

All the '33 water pumps I've seen have the square hole, not the D shaped hole.

 

17 hours ago, DFeeney said:

Hello,  Please note that a 33 Plymouth did not have a by pass.  It was added in 34.

 

And, to the best of my knowledge, the external bypass was only on the PE. I think the PF and PG pumps looked externally the same as the '33 but they might have had the D shaped outlet. But I had thought the D shaped outlet from the pump started in 1935 when they widened the block slightly and added the water distribution tube.

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Hello again,  If you look at a 33 Plymouth water pump it has a one piece body with no outlet or threaded mating surface for the water pump by pass neck which came in 34.

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Wow , Just located my 2  water pump backing plates.  One had the D hole and the other didn't.   Sorry no pictures

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what do you think about the possibility of the difference being if your car would have a heater or not . the pump in the pictures with out the D shaped hole has the heater nipple on the inlet neck. the pump with the D shaped hole does not have  heater hose nipple. the heater does by pass radiator.

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Thinking that heater option may have been rare in 31-32. Not sure.   31 Deluxe had them but late in 31.  Surprised that the Master parts book only lists 1 part number for 31-32   i think I may have another pump with a heater bypass on it.   Have to look around a little.  I'll try to email Plymouth Owners Club   Tech advisor for PAmodels.   Don't know if he follows AACA Forums

 

Wash your hands

 

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i already e-mailed tech advisor bob mcmulkin he didnt know. he just said either one will work and i all ready know that. he did say that it would not have any thing to do with a heater or not.

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the holes in back plate of pump have nothing to do with heater  as my PA the pipe going down to lower rad has a tap which heater hose is attached and returns to tap on head   the block will tell which hole the pump will use to circulate the water through system   square hold is used on 4 cylinder motors     the 6 cylinder block has a half moon looking distribution tube that should be inserted in block    in that  case it would be the only port the pump would use to force the water to circulate       both pumps seem to has a little hole as big as pencel which seems to do nothing

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2 hours ago, broker-len said:

the holes in back plate of pump have nothing to do with heater  as my PA the pipe going down to lower rad has a tap which heater hose is attached and returns to tap on head   the block will tell which hole the pump will use to circulate the water through system   square hold is used on 4 cylinder motors     the 6 cylinder block has a half moon looking distribution tube that should be inserted in block    in that  case it would be the only port the pump would use to force the water to circulate       both pumps seem to has a little hole as big as pencel which seems to do nothing

 

The '33 and, I think, '34 six cylinder blocks had a square opening into the block. The water distribution tube was introduced in 1935, the PC through PF engines don't have that.

 

I am pretty sure one of the pencil sized holes in the backing plate on my '33 is used as a bypass to allow a little water to circulate in the block before the thermostat opens.

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Posted (edited)

As I understand the operation of the mopar motor,,,,,the pump draws water from the bottom of the tank it then pushes the water through what ever hole goes through the block ,,,up the top rad hose to the top of the rad tank then the water falls through the core and so fourth      I have both a 36 and a 32 PA    only one access to block,,,32 is a square and 36 is a half moon     do not remember there being a small hold like the one in middle of back plate---always wandered  what was the purpose

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Edited by broker-len (see edit history)

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the point i am trying to make here is that there are two different backing plates on PA PB water pumps. not just mine but also '' 31 PLY'' and i have seen mutiple PA PB water pumps with both types of backing plates.PA PB water pump is olny for those two years. the 6 cylinder water pump has nothing to do with the 4 cyl cars.i just mentioned it to try to under stand by pass systems. i am thinking one of the backing plates is an inprovement but witch one.

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On 4/4/2020 at 4:19 PM, JamesLay said:

the point i am trying to make here is that there are two different backing plates on PA PB water pumps. not just mine but also '' 31 PLY'' and i have seen mutiple PA PB water pumps with both types of backing plates.PA PB water pump is olny for those two years. the 6 cylinder water pump has nothing to do with the 4 cyl cars.i just mentioned it to try to under stand by pass systems. i am thinking one of the backing plates is an inprovement but witch one.

Here's a picture of the front side od a PA engine if that's helpful.

IMG_3763.jpg

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i have both PA and PB blocks they both have the same square hole round hole set up. i think the pump with the D shaped hole must be later pumps (PB) i installed the backing plate with the D shaped hole i had been running the plate with out the D shaped hole.and see if there is any notable difference in my engine cooling habits.i wont be running the car for awhile weather is still pretty bad here 8 inches of snow today.

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