MCfan Posted January 18 Share Posted January 18 I am in need of some advice regarding an extra feature (hole) in the new water pump I am preparing to install on my '70 402. As shown in the photos below, the new pump is virtually identical to the original pump except for a 9/32" diameter, unthreaded hole in the front top side of the casting. Since it is unthreaded, it may simply be a vent or weep hole but I want to be sure it is not intended to be otherwise functional before I prime and paint the new pump Chevy Orange. The new pump is a GMB 130-1320P which I recently acquired from RockAuto and it is supposed to be a direct replacement except that it has a higher pressure and flow rating than the original. I am hoping that is pump will work, even if I need to tap and plug this extra hole. Can anyone share their insight regarding this extra hole and what its purpose is? Many thanks! Quote Link to comment Share on other sites More sharing options...
jft69z Posted January 18 Share Posted January 18 It appears to just be a weep/vent hole, like you'll usually find on the bottom side. Quick test, blow a little air in that hole, if it comes out the bottom one, all is good. As far as 'high pressure/flow'... FWIW, when I ordered a couple of radiators from Griffin, they were real adamant to use stock type water pumps. They said the higher flow would actually work against you, as there wasn't enough time for the heat exchange process to occur. Perhaps it's more important with their design of radiator, I don't know. Then again, if GM thought their engines needed higher flow/pressure water pumps than already manufactured, they maybe would have made them like that? 3 1 Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted January 18 Share Posted January 18 Paint it, install it, enjoy it. 😎 4 1 Quote Link to comment Share on other sites More sharing options...
MCfan Posted January 18 Author Share Posted January 18 Thanks, Joe and Tom! Yes, it is apparently a vent hole. I had neglected to notice the weep hole on the bottom side of the original pump which is also on the bottom side of the new pump. Air blown in the top hole simply exhasusts through the bottom weep hole. Regarding the higher pressure/flow spec, I really debated before I ordered, wondering if that might create other problems elsewhere in the system. The fact that I had replaced the original leaking radiator (still have it in storage) when I received the car in 2010 with an aluminum unit and that I sometimes see the temperature creep toward the upper limit when idling in traffic on a hot Florida day, swayed my choice in favor of this unit. Guess I'll find out sooner or later if the system can handle it. I just installed a new set of gauges with new sensors/senders so I should be able to tell how it's performing. Thanks again for your helpful replies! 4 Quote Link to comment Share on other sites More sharing options...
jft69z Posted January 18 Share Posted January 18 Let us know if you notice any differences in temperatures. It would be interesting to see what, if anything changes. 1 Quote Link to comment Share on other sites More sharing options...
Leghome Posted January 18 Share Posted January 18 I an old timer tell one time that that hole was for lubricanting the shaft 1 Quote Link to comment Share on other sites More sharing options...
MCfan Posted February 13 Author Share Posted February 13 On 1/18/2024 at 1:19 PM, jft69z said: Let us know if you notice any differences in temperatures. It would be interesting to see what, if anything changes. I completed the installation of a new higher pressure and flow water pump, a rebuilt power steering pump and a higher amp alternator a couple of weeks ago. I've had several opportunities since to drive my Monte ten miles or more and everything seems to be funtioning well with no leaks (fortunately). I was crusing about 55 on a mostly deserted rural road this weekend and decided to snap a photo of my new gauge set that shows the water temperature holding steady just below 170 degrees. That's a nice improvement over the 180+ degrees it used to run. Of course, crusing in 70 degree weather is different than idling in traffic on a 95 degree day, so its nice to have that cushion. So far, I can't see any disadvantages to having the higher pressure, higher flow water pump. 4 Quote Link to comment Share on other sites More sharing options...
jft69z Posted February 13 Share Posted February 13 Dennis, did you get a chance to drive with the old water pump and new gauges, to get an accurate baseline, or were the old 180+ temps you mentioned before with the old gauges? Quote Link to comment Share on other sites More sharing options...
MCfan Posted February 13 Author Share Posted February 13 I had installed the new gauges and sensors about two weeks prior to discovering the blown seal on the original water pump. I was making a 27 mile round trip 3 or 4 days a week and noted that the new water temperature gauge was reading 180 or better. I had been checking the gauges frequently because I had recently changed my motor oil from 20W/50 to 10W/30. I don’t know if possibly some of the higher temperature was due to a less than full radiator which I was topping off weekly due to the leaking water pump. I know what it’s running now and that it has reduced occasional detonation due to the 11.9:1 compression ratio using the same fuel mix. 2 Quote Link to comment Share on other sites More sharing options...
jft69z Posted February 13 Share Posted February 13 That's good, I was just looking for an apples to apples temperature measurement with the same instrument, before & after the pump replacement. Sounds like a success story & thanks for the update. 1 Quote Link to comment Share on other sites More sharing options...
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