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Water pump housing holes

Mike Szadaj

Well-Known Member
Local time
12:44 PM
Jan 17, 2019
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St. Clair Shores, Mi
The water pump housing on my engine has 4 holes. As you can see, one is plugged. I think I should use the front hole and the left hole for the heater hoses, then plug the middle one. I seem to remember at one time Mopars had a bypass hose. Is that why there are 4 holes? Is the hole usage I mention correct for the heater?

Yeah, 67 and 68 WP housings did not have the far left outboard hole. Only 3.

Maybe A/C or something?
This engine is not original to the car. Any kind of changes could have been made. As you can see, the lower radiator tube is on the right side of the engine. The only part of the number cast into the housing that I THINK I can read is last two digits are 88. There is a part number 2780988 housing that was used on 383 - 440 - 426 engines in 1967, 1968, 1969, and 1971. Curiously, 1970 used part number 2951806. The GG white book says the Pentastar was cast into housings 1970 and newer. I guess that means mine is from 1971.

Not sure when they started but truck big blocks had the reverse housing. I would just put a pipe plug in the far left water outlet. Left looking at the picture.

There should also be a date code on the housing somewhere.
AFAIK, that is a 1973 and up water pump housing. I don't think the accessory brackets interchange between '73-up and '72-down, and of course the radiators would be different too. I would install the correct water pump housing for your year of car: 1973-up inlet on pass. side, 1972-down inlet on drivers side.
My opinion....use the left outboard hole for a water temp gauge....a mechanical type with a vapor filled bulb that is immersed in the coolant....like Auto Meter or something similar.
FYI....On B/RB engine the coolant bypsss is internal to the pump housing via a cored hole directly under the t-stat, unlike the LA engine which uses an external hose connection from the manifold to the water pump housing.
Bob Renton
Ma Mopar changed the lower radiator position because in the early 70s, they needed the room on the drivers side for a SMOG pump. Putting the pump on the passenger side would have interfered with the fuel pump.
I'm sure it's fine and at this point it's all moot because obviously you found a solution by now, but... The original picture is a '73+ passenger-side exit water pump housing. The heater hose pipes go on the far outer (1/2") and bottom (3/8"). The middle hole is where the OSAC valve goes.