# 65 GTO 389 Water Pump Plates?



## Roqetman (Aug 31, 2015)

I recently replaced all the hoses on my 65 and decided to also put new stainless steel divider plates in the water pump. I've read where the plates have to be adjusted and set for a certain clearance. They seem to fit just fine. How is the clearance set and at what measurement? I've also read that a 3/32 hole needs to be drilled in the divider plate, the ones I took out did not have this. If the hole is needed where should it be drilled? When I run the engine I'm getting "whumping" noise that seems to come from the heater hose. Could that be air in the cooling system? How's the best way to bleed air out of the system?
Sorry for all the questions. Thanks for your help! Roqetman


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## bigD (Jul 21, 2016)

Haven't read anything about that hole you mentioned. I have read that some drill a hole in the thermostat.

https://www.google.com/search?q=doe...ome..69i57.16805j0j4&sourceid=chrome&ie=UTF-8

Some say they have seen as much as 1/4" clearance between the plate & impeller fins. Most say it should be no more than .100", for proper pump function. Less is better, as long as there is no contact at any time.

The fix is pretty simple. You hammer the plate in, as needed, to reduce the clearance distance. 

Water Pump Mods

Water Pump Mod - Second Generation Pontiac Firebird (1970 - 1981) - Firebird Nation

The clearance mod for early and late style plates is basically the same.


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## Roqetman (Aug 31, 2015)

BigD, Thanks for the information, very helpful! Also, since the 389 has an inner plate that fits inside the timing chain housing and an outer plate that fits against the water pump, is it recommended, or not, that they be adhered together with RTV? If not, what is recommended clearance between this two plates? I would think they should be very close in order to maintain a tight clearance with the water pump vains.

Thanks, Roqetman


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## bigD (Jul 21, 2016)

Sorry, I can't help you with that info. I've always used the later 11-bolt cover & pump. But, there are probably lots of guys here who have experience with the 8-bolt stuff.


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## geeteeohguy (Feb 2, 2008)

No RTV. The plates nest together, and bolting up the water pump holds them in place. I use a crescent wrench and go around the opening radially to set the clearance on the front plate. I also coat the inside of the timing cover with Glyptal to prevent the aluminum from corroding due to electrolysis.


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## Roqetman (Aug 31, 2015)

Geeteeohguy, thanks for the info. Upon dismantling the water pump I discovered that the new S/S plates did not fit very well inside the timing chain cover. The big "ear" on outside plate had compromised the gasket causing a leak and had to be ground down in order to fit. I also noticed that the inside plate did not have a cut out at the bottom of big opening like the old one did. Not having the cut out caused the plate to contact the inside of the timing chain cover, so it wouldn't seat properly. I spend a good bit of time test fitting, marking and grinding spots to be clearanced. The pics below show the old plates versus new plates after tweaking. My 389 pump has the stamped steel vains and appears to be in good shape. The clearance between the blades and the plate is approx 3/16". But... it is worth replacing the pump to get a cast impeller?


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## Pinion head (Jan 3, 2015)

Rogetman, the clearance between the impeller blades & the divider plate is critical for efficient cooling. I've used one of my body hammers & a block of wood to back it up to bump the 11 bolt divider plates to an acceptable clearance on mass-rebuilder pumps with the stamped impellers. 

For my own Pontiacs & those of friends, have been rebuilding original casting waterpumps with the correct cast impeller. Have many many cores. There were at least 5 different cast impellers Pontiac used from '63-81. 64's, for instance, used their own specific impeller due to the design of the '64 radiator. Am doing another rebuild run later this week.


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## Roqetman (Aug 31, 2015)

Pinion head, thanks for your reply. I see where NAPA offers a new pump with cast impeller for about $60. One of my main concerns was having to cut out the section of the plate that was hitting the cam cover. Have you had to do this on '65 389s?


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## Pinion head (Jan 3, 2015)

Have never ran into having to cut on a divider plate. Have not used the stainless dividers either, still have several nice used steel divider plates for the 8 bolt pumps. as well as several nice 8 bolt timing covers. On the original casting 8 bolt pumps, we use an original large divider plate as a cking feature when pressing the correct cast impeller back on.


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## geeteeohguy (Feb 2, 2008)

Late to the party here, but the original plates pictured are in good shape. I would clean them, spray them with Glyptal, and re-use them. Much better than repro parts, IMO.


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