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Thread: 6.5 water pumps

  1. #1
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    Default 6.5 water pumps

    I would really like to know if there is a true factual basis for why the 4 stud style water pump flows with a supposed huge flow bias where the thread on style does not. I would think that a picture should show immediate differences if there were any. There are 6.5 vendors out there that make statements about the 6.5L cooling system that they cannot prove. They may talk about testing, but provide absolutely no factual data or proof of how the tests were performed etc. They just make bold statements.

    Last edited by Kennedy; 10-04-2018 at 09:51.
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  2. #2
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    In the case of the 6.5 water pump I would think that the simplest place to start is by building a rig where the water pump moves water from the lower rad hose through equal sized pipes with flow meters first in order to see if the supposed imbalance is due to pump design or not. My speculation is that the results would show little to no difference.

    From there other tests could probably be performed, but by my way of thinking there's just no way that you can take a centrifugal pump and bias the flow or pressure to one side or the other without a major (and obvious) change in casting passages and even then...
    Last edited by Kennedy; 10-04-2018 at 10:05.
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  3. #3
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    Arrow Trust but Verify

    I would really like to know if there is a true factual basis for why the 4 stud style water pump flows with a supposed huge flow bias where the thread on style does not.
    I'd like to know that too.

    Logically... If I were selling 6.5 cooling widgets, and made some claim, I'd have the data - verifiable - provable/reproducible data for which the claim is based. I'd also have a series of images that show that we actually did the test. Doing a quality data collection project is a lot of work. If you're "in the business", you would not waste that effort by not collecting images and data.

    Our own Pull-Off Series was done in front of everyone interested in GM diesel performance. Some got to ride along, use their own stopwatches and even look over the shoulder of the driver to record speed and engine data. We also did an instrumented fuel economy data analysis where we measured fuel use with a 6.5L diesel on an engine dyno at various engine speeds and loading. We did that test in front of dozens of you guys.

    It's amazing that some 6.5L diesel owners don't apply logic when looking at ad claims.

    Edit: There are a couple other topic threads in our 6.2L/6.5L Tech forum related to "being curious" about ad claims:
    https://www.thedieselpageforums.com/...splay.php?f=22
    Last edited by More Power; 10-04-2018 at 17:13.

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    The only difference I "saw" was a larger impeller than the early 4 bolts, but the later 4 bolts "should" have a HO in the casting, these are said to be the better flowing 4 bolt units.



    With the Humvee fan system I am using I will be staying with the 4 bolt version.



    Nice work John glad to see this kit come back !
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  5. #5
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    What do you all think about the "restrictor in the bypass" on the HO pump / dual t-stat setups?
    1987 Jeep Grand Wagoneer...new 6.5 in process...diamond block, 18:1's, other goodies...


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    As luck would have it, I have both a 1997 "HO" 130-gpm 4-bolt-fan water pump and a newer screw-on-fan 130-gpm high output water pump for the 6.5 sitting on my work bench.

    The impellers are exactly same diameter, thickness and appearance. The coolant flow passages, dimensions, appearance and every other detail appear exactly the same between the two pumps.

    I'll have close-up pics sometime this weekend, that I'll post to this thread.

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    Quote Originally Posted by JeepSJ View Post
    What do you all think about the "restrictor in the bypass" on the HO pump / dual t-stat setups?

    Myself I think it's a bad idea and giving a false sense that things are running cooler when the head is actually running hotter.



    Why would restricting water flow anywhere in the system be a good idea? The block off type were taken out of use for a reason, I don't know for sure but I would bet it was to incress flow through the system..
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  8. #8
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    I have a photo here of the early 80 gph pump with the later 130 gph pump right next to each other:



    These are both flange style with studs. The one on the left is the 80 gph pump. It's impeller is just under 3.9" in diameter. The one on the right is the 130 gph pump and has "HO" cast into the front of the housing. It's impeller is 4.25" in diameter. I don't have a spin on type available to photograph (the one I have is on an engine), but the last time I compared them, as Jim says, they were the same as the one on the right in the photo above.

    As you can see from the photos, the discharge passages are symmetrical, so there really shouldn't be any difference in flow from one side to the other (unless black magic is involved... and I don't believe in black magic).

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    Quote Originally Posted by JeepSJ View Post
    What do you all think about the "restrictor in the bypass" on the HO pump / dual t-stat setups?
    https://www.thedieselpageforums.com/...ad.php?t=45811

    This thread discusses this topic.

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    The following image shows a comparison of both high-output water pumps available for the 6.5L diesel. On the left is the integral pulley style and on the right is the 4-bolt fan style with the letters HO cast into the flange.

    As Ron said, the impellers are 4.250" in diameter - both of them.



    I'm also linking a full-size image, so you can zoom in.
    https://www.thedieselpage.com/images/WPBias04c.jpg

    The water pump on the left was a very early version of the integral pulley style. It looks a bit grody because it was on a test engine that GM used to evaluate the engine's ability to deal with corrosive road spray. This WP came from Peninsular. GM, as the story goes, put the engine on an engine stand, and ran it at some power level in an environmentally controlled booth that sprayed some nasty corrosive crap onto it for some length of time. This is partly why the production engines all came with sealed electrical connectors. While the water pump suffered some amount of corrosion, it is still a mostly new unit... I keep it around thinking a little bead blasting and a fresh coat of paint would do it wonders.

  11. #11
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    John,

    I purchased a new "high output" water pump from you this summer, but it did not have "HO" stamped into the water pump. I have a 1997 take-out engine, and it does have "HO" stamped on the OEM pump. Should I be concerned that the new pump is not actually marked with "HO"?

    I compared the impellors from the old 1995 pump to the new replacement model, and the new model was definitely larger.

    Thanks!
    1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter

  12. #12
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    I've seen some aftermarket pumps recently that didn't have the "HO" cast into the front. As long as the impeller is the right size, it should be OK.

    I recently bought one for a customer truck. This truck is a late 1996 model that came from the factory with dual thermostats and HO pump. Someone along the line had put a new water pump on it. Customer said it had run hot since that time. I pulled the pump and it was the old style, small impeller (actually, the one in the picture above). I found an AC Delco pump on rock auto (the other one in the picture above) that has HO in the casting rather than trusting the local parts stores to get the right thing. They had no idea what I was talking about (probably why the wrong pump was installed in this truck the last time). I have also learned that the GM 8 digit part number is no longer available. The AC Delco pump is the same thing, just made through their aftermarket supply chain.

  13. #13
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    Quote Originally Posted by Kennedy View Post
    I would really like to know if there is a true factual basis for why the 4 stud style water pump flows with a supposed huge flow bias where the thread on style does not.
    I think it is pretty clear that this is a myth.

  14. #14
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    Quote Originally Posted by arveetek View Post
    John,

    I purchased a new "high output" water pump from you this summer, but it did not have "HO" stamped into the water pump. I have a 1997 take-out engine, and it does have "HO" stamped on the OEM pump. Should I be concerned that the new pump is not actually marked with "HO"?

    I compared the impellors from the old 1995 pump to the new replacement model, and the new model was definitely larger.

    Thanks!
    Simple test is 4.0 versus 4.25" impeller which can be measured with a tape rule or just visibly compared.
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    Question, has anyone sliced the different pumps in half to see if their is any differences we can't see?



    Also, I know the impellers are a different size but they all have 6 vanes.



    I have a "FlowCooler" pump here, much different impeller design. CNC 10 vane impeller and the body is machined and the impeller is thicker than the others, it measures a little over 4" wide.



    If anyone has a old screw on type pump laying around I would pay to have it shipped so I could cut the 3 different styles in half and compare them...
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    Quote Originally Posted by sctrailrider View Post
    Question, has anyone sliced the different pumps in half to see if their is any differences we can't see?



    Also, I know the impellers are a different size but they all have 6 vanes.



    I have a "FlowCooler" pump here, much different impeller design. CNC 10 vane impeller and the body is machined and the impeller is thicker than the others, it measures a little over 4" wide.




    If anyone has a old screw on type pump laying around I would pay to have it shipped so I could cut the 3 different styles in half and compare them...

    Interesting concept, but not sure why they would choose the smaller diameter impeller design? Looks like they used the late casting and left a large clearance.
    Even if they exceed the original design, appearance is everything.
    Kennedy Diesel-owner
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  17. #17
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    Quote Originally Posted by Kennedy View Post
    Interesting concept, but not sure why they would choose the smaller diameter impeller design? Looks like they used the late casting and left a large clearance.
    Even if they exceed the original design, appearance is everything.
    I'm no engineer, but leaving a large clearance between the impeller outer edge and the pump housing (the orange colored impeller) can't be good for either flow or cavitation.

    Obviously, a lot of effort was expended on design of the orange impeller. I'd like to see the test setup and data that compared the flow rate with a stock HO pump.

  18. #18
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    Yea, I wondered that also, I may give them a call and see what they have to say..



    I don't have a way to test the flow of any of the pumps, I'm investigating how a setup could be installed on a running motor without spending a lot of cash.. I wouldn't mind changing pumps a time or two, but with my humvee fan system I can't use a spin on type pump...
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  19. #19
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    My guess is that like most products it was designed/engineered for a more mainstream application: the SBC Then I would assume adapted (quite poorly) to the 6.5 application. Maybe they used a standard size impeller or maybe they used the older 6.2 as a pattern, but rather than create a proper diameter piece it was left as is.

    My guess is that when it comes to impelling water flow the end clearance is less critical than the side clearance but to what extent???
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  20. #20
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    Tip clearance is critical. This large clearance will allow flow recirculation which hurts efficiency and capacity.

    I would like to the see the impeller from the front. It looks like it might be a shrouded design which can improve flow. However, the large tip clearance probably loses everything that they gained. Again, the shroud thought is just a guess, since I can't see the front.

    Automotive water pumps are generally quite crude when compared to even centrifugal well pumps. It seems to me there is a lot be gained there. Cost is a major driver in automotive production.

    Oh, and by the way, I am an engineer.

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