Water Pump Impeller Rotation Conflicting Info

Elizabetty

Registered Member
Original poster
Dec 2, 2022
132
Wisconsin
Shopping rockauto and finding differences that lead me to Google and ultimately I wind up here.

My vehicle's specs at multiple auto part sites bring up these three water pumps I'm interested in. I attached pics.

The original GM part states the impeller rotation is standard. The AC Delco states reverse impeller direction. The Gates states standard rotation.
2 standard
1 reverse

There's a pic from the Hayden fan clutch that has a pulley diagram to help determine the style water pump. I have the smooth pulley where the back side of the belt is making contact. According to their diagram and everything else I find online, this would mean my water pump is reverse rotation and it's my understanding the rotation is in regards to the impeller.

Info I found elsewhere:
"A serpentine belt accessory drive where the SMOOTH side of the belt is turning the water pump will require a reverse-rotation water pump."

I originally was going with AC Delco and had changed to Gates but now I'm thinking I need to go back to AC Delco. However, it can't possibly be that the GM standard rotation is incorrect right? So do I go back to Gates cuz it matches GM?

If I look at the GM fan clutch instead of the Hayden, it states it is counterclockwise. Hayden states it is reverse which in my mind would mean counter clockwise. I assume this rotation is in regards to the direction the blades are spinning when facing the front of the vehicle. Currently, my fan spins to the left, which is counter clockwise, while facing the engine. Their fan specs match. I could safely buy either one. BUT: If the pulley information in the Hayden picture is correct, it should translate to the similar spec GM fan. That would mean my engine has (should have) a reverse rotation water pump which would mean I should be going with AC Delco as my replacement instead of the GM original part? How does that make sense? The only other thing I can think of is if there is a secondary meaning to water pump rotation aside from the impeller direction? I've yet to find what that would be.

If by some reason I have a standard rotation water pump (meaning impeller rotation) when I should have a reverse rotation, couldn't that have something to do with why my engine coolant temperature sensor and thermostat are both fine, I don't have coolant leaks or pressure issues, yet I have unstable temperatures, typically on the low side? Wouldn't the potential of incorrect impeller direction mean a lack of coolant flowing adequately in order for those pieces of the puzzle to work?

Editing to add that I do understand a low coolant situation would lead to overheating. I realize I typically under heat and I'm going to be told thermostat and sensors. Please wrap your head around what I'm trying to understand aside from engine temperature when it comes to the function of the parts as a system. I'm trying to understand a bit further into what weak flow could do. I know there's a difference between reverse flow and reverse rotation. I'm not asking about reverse flow. I'm simply asking about the rotation because the flow of the engine coolant will maintain its original design but an impeller that is essentially backwards for its setup would have a hard time moving the coolant or even maybe move it too quickly for what it actually needs? I'm not sure.

Help.
 

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Last edited:

Matt

Guru
Dec 2, 2011
3,959
Don't put too much thought into it.
This is the difference, as you can see, they actually rotate the same way. Just get the OEM one and be done with it.

V-Belt-water-pumps-and-rotation_copy_large.jpg
 
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Elizabetty

Registered Member
Original poster
Dec 2, 2022
132
Wisconsin
Don't put too much thought into it.
This is the difference, as you can see, they actually rotate the same way. Just get the OEM one and be done with it.

V-Belt-water-pumps-and-rotation_copy_large.jpg
I appreciate the time taken to respond, but that would make me a part swapper with no knowledge and I'm trying to understand this difference. Afterall, it's not like I'm talking about some off-the-wall company compared to a GM part. I'm comparing GM and ACDelco which are hand in hand and offer 2 options with different specs for 1 vehicle.

If I add circumstance to it, one could say I buy GM GENUINE 251731 GM Original Equipment today and then if it fails for whatever reason and I'm broke, I buy ACDELCO 252822 Gold / Professional, I literally have 2 completely differently operating water pumps. The water pump is essential. I would like to learn and understand the difference before using one style one time and another the next. Afterall, it is not uncommon to hear of water pump failure multiple times for some folks, right alongside fan clutch, so perhaps there's a relationship reason worth understanding.
 
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Mooseman

Moderator
Dec 4, 2011
23,693
Ottawa, ON
They are all the same. I don't know why they include impeller rotation direction because they are all the same. Just different terms used by different makers for the same thing. All Atlas engines use this same pump and rotation.

BTW, don't bother paying the premium price for the GM part. ACDelco is GM's supplier and a 1/3 of the price.
 

TequilaWarrior

Hobbyist
Dec 5, 2011
511
Central Pennsylvania
Impeller rotation becomes a concern if you're making substantive changes to belt routings - which you're not really going to do with this platform. If you were building a drag car, and were setting up the accessories for the engine (say, in order to provide frame or header clearance, perhaps to include a power steering pump but not an A/C pump), you may be in a position to choose pully sizing, routing, etc... in that case, water pump rotation would matter. If you're "swapping parts" and keeping everything stock - or even remotely close to stock - a water pump is a water pump.

This is when pump rotation matters:
2023-01-24 11_14_31-Underdrive, Serpentine & More Pulley Kits at Summit Racing — Mozilla Firefox.jpg
 

Elizabetty

Registered Member
Original poster
Dec 2, 2022
132
Wisconsin
Thank you. After stepping away from the documentation and going only by images, I do not see any difference in impellers even though the documentation has different information.
 

movietvet

Registered Member
Dec 21, 2022
171
Oregon
If I remember right, you have a 2002 TB, like my girl does. I bought and installed the Genuine GM part #251-731, I tend to get Genuine GM when available because I am a thousandaire, and I also replaced the water outlet/thermostat part #15-11006. I watched you tube videos and also got info here about unbolting the fan clutch during removal for easier access, instead of hacking the fan shroud. It went just fine. Make sure you have a fan clutch tool when you do it. I have had no problems since the install and the water leak I had at the old pump weep hole is gone.
 

TJBaker57

Guru
Aug 16, 2015
2,241
Colorado
Without actually reading all through this thread I would believe that "standard" and "reverse" have nothing to do with clockwise vs counterclockwise per se.

I see "standard" meaning the pump spins the same direction as the crankshaft and reverse means the pump spins the opposite rotation of the crankshaft.

Look again at @Matt post image of standard and reverse. The pump in those images do NOT spin the same way.
 
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Reprise

Lifetime VIP Donor
Jul 22, 2015
2,643
At the risk of beating the dead horse... match up the belt routing as per Matt's diagrams, then compare to your own. (If needed, there s/b a routing diagram on either the fan shroud or a decal on the front bulkhead). Then compare the orientation / impeller direction of the old WP, as the belt routing would apply to it.

AFAIK, there is only one standard routing each for I6 and V8, so things *should* match up well. Finally, when you get the new WP, compare it to the old, as a final check.
(and from a logic standpoint, you're correct to think that there should not be two versions of belt routing (at least for a std / OEM config). But there is ostensibly some purpose for putting it there, so... it exists.

We won't go into the how / why -- or even if it's valid (e.g.; 'the internet is infallible' canard. And no slight to Matt, of course!)

Also no slight to you -- the descriptions *are* confusing, and I'd be exercising due diligence, myself.

Finally, I personally have no issue with a Gates WP -- I have 2 in-use on my V8s, and Rock honors their warranty without issue, if you buy from them (their system remembers your purchase, forever). I have to give RA credit for that much, at least. But there's no shame in getting ACDelco, if you're anxious -- the R&R is more difficult on the 4.2 vs the V8, to be sure -- no one wants to do it twice.

Oh, and since you've evac'd the coolant, a new t-stat wouldn't be a waste, since you're reporting chronically low temps (suggesting that it's stuck open.) If you see a TON of corrosion on the innards of both the WP and t-stat, figure that the prior owner neglected to change the coolant, and that providing an answer as to why both went bad. Otherwise, if you know the coolant is good (e.g.; you replaced it), then reuse it.
 

mrrsm

Lifetime VIP Donor
Oct 22, 2015
6,371
Tampa Bay Area
@Matt is Right... By following an "Occam's Razor" approach in this case... The easiest way to remember which direction ANY Accessory bolted to ANY GM (Clockwise) Rotating Crankshaft Engine Blocks is THIS:

"If the Accessories or Water Pump Pulley to Belt Contact is SMOOTH (No Serpentine Grooves) then the Accessory and Water Pump Impeller Rotates Counter-Clockwise"

So in the GM Atlas LL8 4.2L Engine Block... there are just THREE such items that will do this:

(1) The Belt Tensioner - Pulley
(2) The Alternator Idler Pulley
(3) The Water Pump & EV Fan System

GMATLASLL8BELTANDPULLEYS.jpg

Back in the Late 1990s when Mr Ron Kociba and his Atlas Engineering Team where slogging through their thoughtful design of this amazing "Lost Foam" Aluminum Cast Engine.... He realized that with a 10.1 to 1 High Compression Ratio (and a desire to Burn Cheap Gasoline)...they'd have to keep the Engine Coolant as hi as 210 Degrees for the Highest Fuel Efficiency and NOT Warp the LONG Aluminum Engine Head, nor suffer from 'Engine Knocks and Pings'.

So this meant they would need to Introduce Coolant into the Engine Head FIRST (see photos). Note that the ACDelco Water pump fits into a Strange Chamber-Cavity such that it can drive the coolant in the right direction. Take note of the proximity and directions of the WP "Vane Buckets" as they push fluid through a chamber "Swirl" necessary to maintain coolant velocity and keep liquid things moving through the Engine Head and Block to eventually drive the coolant through the Radiator and satisfy the necessary Heat Transfer. Here are some more intimate images to help to amplify the discussion (if necessary):

ACDELCOLL8WPANDGASKET1.jpgACDELCOLL8WPINTERIOR1.jpgACDELCOLL8WPGASKET.jpgGMLL8TIMINGCOVERINTERIOR1.jpgGMLL8TIMINGCOVEREXTERIOR1.jpgGM42LFRONTBLOCK1.jpgGM42LFRONTBLOCK2.jpgGM42LFRONTBLOCK4.jpgGM42LFRONTBLOCK4OBLIQUE.jpgGM42LFRONTBLOCK4OBLIQUE2.jpgGMLL8WPPROXIMITYTOTHERMOSTAT1.jpgGMLL8ENGINEHEADCOOLANTINLET1.jpgGMATLASSLL82.jpg


"Round and Round She Goes... Where She Stops? Nobody Knows!"
 
Last edited:

budwich

Guru
Jun 16, 2013
1,816
kanata
but the question still remains.... what type of water pump does the OP actually has in the vehicle and is it indeed the "right one"... what ever that means?
 
Last edited:

Mooseman

Moderator
Dec 4, 2011
23,693
Ottawa, ON
I think you're still reading too much into this. What she has and what she will get is the only pump available for this engine. Doesn't matter if it;s reverse or standard rotation.
 

movietvet

Registered Member
Dec 21, 2022
171
Oregon

Beacon

Active Member
Mar 22, 2019
420
SouthWestern PA
last line of the chart

ACDELCO 252822 Specifications
Casting Number18-1638
Fan Clutch IncludedNo
Housing MaterialAluminum
Hub Height54.86
Hub Height (IN)2.165
Hub Hole Quantity4
Impeller MaterialSteel
Impeller RotationReverse
Impeller Vane Quantity6
Includes Back HousingNo
Mounting Hardware IncludedNo
Mounting Hole Quantity5
Outlet Quantity0
Pulley Included?No
Remanufactured?No
Thermostat And Housing Included?No
Water Pump Drive TypeTiming Belt

 

movietvet

Registered Member
Dec 21, 2022
171
Oregon
Wow, I see that now. I missed it. But we both know it is wrong.
 

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