6.5 water pumps

[Kennedy]

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.

[Kennedy]

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...

[More Power]

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/tdpforum/forumdisplay.php?f=22

[sctrailrider]

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 !

[JeepSJ]

What do you all think about the "restrictor in the bypass" on the HO pump / dual t-stat setups?

[More Power]

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.

[sctrailrider]

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..

[ronniejoe]

I have a photo here of the early 80 gph pump with the later 130 gph pump right next to each other:

http://www.schoolcraftpowertrain.com/Pictures_&_Data/2018-09-29 10.00.38.jpg

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).

[ronniejoe]

What do you all think about the "restrictor in the bypass" on the HO pump / dual t-stat setups?

https://www.thedieselpageforums.com/tdpforum/showthread.php?t=45811

This thread discusses this topic.

[More Power]

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.

https://www.thedieselpage.com/images/WPBias04smc.jpg

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.

[arveetek]

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!

[ronniejoe]

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.

[ronniejoe]

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.

[Kennedy]

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.

[sctrailrider]

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...

[Kennedy]

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.

[More Power]

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.

[sctrailrider]

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...

[Kennedy]

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???

[ronniejoe]

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.

[More Power]

I found the link to a story I wrote in 2008 that addresses this topic.

https://www.thedieselpage.com/features/dualstats.htm

[ronniejoe]

Mr. Fuller is/was a training instructor. He can offer some good insight. However, his comment about the "coolant flows through the engine with no restriction whatsoever and travels too quickly to absorb enough heat" is not sound from an engineering perspective. Faster fluid flow is associated with increased convective heat transfer coefficient which means increased transfer of heat through convection from the cast iron surfaces to the coolant. I've heard this "old wive's tale" before. It simply doesn't make any sense.

The reason that you shouldn't leave the thermostats out is that to perform best with highest efficiency, the engine operating temperature should be regulated to the design specification. That's what the thermostat does.

[JohnC]

Mr. Fuller is/was a training instructor. He can offer some good insight. However, his comment about the "coolant flows through the engine with no restriction whatsoever and travels too quickly to absorb enough heat" is not sound from an engineering perspective.

Very diplomatic!

The same logic would argue that, to keep cool in the summer, you should run your fans as slow as possible so the air has more time to absorb heat from your body...

One other thing that some thermostats contribute is blocking off the bypass passage as the engine temperature increases, forcing more coolant through the radiator.

[john8662]

Glad to see very like minded conversation about the two HO pumps. I too have heard that the spin on pump is balanced flow and argued the point that there is no proof of that. I need to see some proof myself that it does flow any different than the 4-bolt pump.

My current logic is the spin on pump was just an industry change that favored that design is all. I think that change is impractical, as I like the 4-bolt setup as it's easier to service for me, at least with common tools.

I've been studying the water pump designs like pictured in these postings this year myself, mainly to gain a better understanding of design changes. The study came about in justifying and seeing the function behind the Peninsular v-belt water pump that I now own the tooling for.

I got the misfortune recently of having to produce a new pattern for the cast iron impeller wheel that goes into the Peninsular pump, so I had to justify the engineering behind it and of course the economics of production to continue the item.

The design engineering spec sheets call for closing the gap between the impeller and the housing. In looking at an 80's v-belt AC Delco pump, I can clearly see why they did it (lots of gap similar to the 80 gph serpentine pump pictured in these threads). I too am behind RJ's engineering on a smaller gap being ideal. Other than the wheel being larger to fill the void the wheel has some other design changes.

This coming summer I am considering doing a test with a variable speed DC motor with the water pumps. have to machine pulleys for the motor and pumps tho...

Anyone know what the RPM the pumps form their rating? For example at what RPM does the HO pump produce approximately 130GPM?


J

[ronniejoe]

The spin-on fan clutch design was done purely for speed of assembly during production, plain and simple. There is no performance difference at all, but they save time during assembly. It makes service more difficult, but that really isn't a concern for the decision makers.

[DieselDobro]

OK, I've been watching this thread and waiting for someone to take it a step farther and bring up the fact that there is TWO spin-on fan AC Delco HO water pumps.
'97 - '99 trucks spec out to a P/N 252776 or 88926290.
2000 and newer 6.5 truck and other applications call for a P/N 251603 or 12456231, 19168609 or 88894035.
Both are HO spin-on fan water pumps. Except the 251603 is $120 more roughly and it carries claims by the over-industrious (in my opinion) 6.5 aftermarket crowd that it is THIS ONE that is balanced!!!

My mind is blown on this thing! I have bought both...the '99 version is still hanging on my truck on the 2009 6.5 Optimizer I just installed (tested) used and turned out to be a dud!
I don't see a difference in the new GEP take off I bought 5-6 years ago from Peninsular and had on my GM block for 3 years. By the way, when I pulled it off the impeller had signs it was rubbing the backing plate and had some radial play in the bearings. So it did not get re-installed with only 20,000 miles on it.

I've been a 6.5 owner for 21 years now continuously and have seen a lot of products and claims made for and about the "performance" upgrades of this and that. There are core improvements that can be made to increase user satisfaction to be sure. Cooling is one of them. This "balanced" water pump thing seems unsubstantiated when it comes to one spin on fan HO water pump to another. Likewise, I can't believe the bolt-on 137 GPM pumps are any different.

Now.. I just need to finalize the deal to get a good (new I hope) long block from the seller I'm working with who sold me the dud, and who shall remain un-named at present, and redo all the gut-wrenching, sleep losing work I just did...AGAIN!!

[DieselDobro]

Here is the GM technical information difference between a 1999 and a 2000 water pump.
Anyone here have any clue what the real technical difference is?

[arveetek]

Here is the GM technical information difference between a 1999 and a 2000 water pump.
Anyone here have any clue what the real technical difference is?

The only difference I see is that 19168610 takes a bolt-on fan clutch, whereas 19168609 takes the thread-on fan clutch and comes with a pressed-on belt pulley.

Casey

[DieselDobro]

Casey, they are both spin on fans...
I have bought both of them.. one sets on the turd Optimizer I just put in my truck. The other is setting on my desk in my shop. I can't physically work on my truck for a couple more weeks but having looked both of them over and the GEP take off I bought from Peninsular a few years back I can't tell any difference.

By the way, I'm trying to get the question answered through AC Delco's "customer support". Yeah, hilarious, right?
That's right they just refer me to call a service facility (GM dealership). What a waste of time, and yes I've done that, too!

[sctrailrider]

I still plan to cut each one in half to compare the insides but I'm covered up and haven't had the time yet..

[arveetek]

Casey, they are both spin on fans...
I have bought both of them.. one sets on the turd Optimizer I just put in my truck. The other is setting on my desk in my shop. I can't physically work on my truck for a couple more weeks but having looked both of them over and the GEP take off I bought from Peninsular a few years back I can't tell any difference.

By the way, I'm trying to get the question answered through AC Delco's "customer support". Yeah, hilarious, right?
That's right they just refer me to call a service facility (GM dealership). What a waste of time, and yes I've done that, too!

I'm just basing that off a google search. Pictures of part # 19168610 all come back as a bolt-on fan clutch.

https://www.google.com/search?q=19168610+water+pump&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjQwcmBnvXfAhXr24MKHfjGDIgQ_AUIECgD&biw=1920&bih=963

Casey

[More Power]

...This "balanced" water pump thing seems unsubstantiated when it comes to one spin on fan HO water pump to another....

Balanced.... ask for the data. Ask for photos of the testing equipment and of the test engine equipped with the flow meters. What engine was used for the test? What engine speed? And on and on... so many questions...

GM (& AC-Delco) began producing many of their water pumps and many-many other parts in China some years ago. A different part number could be reflective of that. I replaced the water pump on my daughter's Malibu 3 years ago with a new AC-Delco unit. It was made in China... I replaced the water pump on my 2001 GMC Duramax a couple of years ago using a new AC-Delco unit... It too was made in China.

See: https://www.bing.com/search?q=ac+delco+gm+parts+made+in+china&form=IENTHT&pc=EUPP_HRTE&mkt=en-us&httpsmsn=1&refig=2fdbe08c607f4ff0daf40bf821fed644&sp=-1&pq=ac+delco+gm+parts+made+in+china&sc=1-31&qs=n&sk=&cvid=2fdbe08c607f4ff0daf40bf821fed644

[DieselDobro]

AC Delco has no product support that I have shook out of many trees I have shook.

[DieselDobro]

Yes, I did note both the AC Delco 252-776 and the 251-603 pumps were Chinese. Both are HO spin-on fans.

The 251-603 pump some internet vendors claim is "a balanced pump" and claim the 252-776 is not.
Having bought both, the 252-776 pump which is actually $100+ cheaper appears to be better quality and even comes with a brass bypass fitting and better quality gasket. There is no visual difference between the two Chinese AC Delco's except I think the Chinese quality of the cheaper pump is better!

Is there a US made or higher quality alternative? None I'm aware of.
OEM's move legacy parts to cheaper production. No surprise there.

[DieselDobro]

BTW, both pumps were purchased from Rock Auto who makes no claims whatsoever about "being balanced" on either pump. Sorry vendors, I love Rock Auto and getting as good of parts for a lot less $$.

[More Power]

Yes, I did note both the AC Delco 252-776 and the 251-603 pumps were Chinese. ...

I suspect the different part numbers reflect different manufacturing plants... in China. Different part numbers allow ACD to keep track of who does a better job (parts return percentage, etc.).

[DieselDobro]

Thats' the first logical answer I've heard on this yet! Thanks, Jim.
Funny...They are $120 different on RockAuto, even. And I think the cheaper ACD is better looking quality wise!

[More Power]

Thats' the first logical answer I've heard on this yet! Thanks, Jim.
Funny...They are $120 different on RockAuto, even. And I think the cheaper ACD is better looking quality wise!

The most recent Chinese water pumps do, in fact, look great and of high quality. But it's what we don't know about them that worries me.

For example, the drive gear on the GM factory Duramax water pump was obviously installed using heat. The flame marks are evident. The hot/cold expansion properties were used to ensure a super tight press fit onto the impeller shaft. The AC-Delco Chinese water pump shows no evidence of a heat application on the drive gear/shaft (the Dmax water pumps are gear driven).