New water pump 6 impellers whats up with that!

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my5thmopar

my5thmopar

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I have been to oreilly's, autozone and advance trying to buy a new wp. I asked for a new wp for a 1972 Dart 318 with a/c. Each time the new pump is a six impellers. None of the stores can tell me why? The only way I could get an 8 impellers is buying a re-manufactured. The 8 impellers was listed on Oreilly web site but was unavailable to order. The 6 impellers looked taller (deeper) than my stock 8 impellers. Also the hole behind the new 6 vane is larger and the depth of the housing is more. Now I'm confused of what to do. Do I need to order something different? Just go with the new style 6 impellers which says meets or exceeds oem flow rate. Store can't tell me flow rate either. I really don't want a reman. I only wanted a new $40 pump. Need this week.

Craig
 
The blade count is only part of the picture. Six taller blades can move more volume than eight shorter blades.

The intake area, discharge path & impeller clearance all play a part as well.

It is entirely possible to have a six blade impeller that moves more water than an eight blade of the same diameter.

Buy the six blade pump & run it.

.
 
Actually, there is a difference in the impellers for a reason. A/C cars have smaller waterpump pullies so the fan spins faster, which moves more air through the radiator at low speeds. This helps keep the engine cool and helps the A/C work better in traffic. Since the water pump is also spun faster, they put more blades, but make them smaller to avoid pump cavitation. I learned this from a old-timer that has been messing with Mopars since the 50's.

I would get the same kind of impeller you currently have. Have you tried Rock Auto?
 
I will. I ordered one from Oreillys last week and it was suppose to be an 8 vane but it was substituted with a 6. I'm being told that they are redesigned and all are 6 vane. I'm still uneasy about using a 6. Will keep ya posted. The one I ordered Monday is going to be shipped from Cardone......we will see. I'm wondering if anybody here is already using a new 6 vane on an A/C car. Chime in please.

Craig
 
my5thmopar said:
I will. I ordered one from Oreillys last week and it was suppose to be an 8 vane but it was substituted with a 6. I'm being told that they are redesigned and all are 6 vane. I'm still uneasy about using a 6. Will keep ya posted. The one I ordered Monday is going to be shipped from Cardone......we will see. I'm wondering if anybody here is already using a new 6 vane on an A/C car. Chime in please.

Craig
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Thanks Craig and I'll let you know if the one I get is a 8 blade also. If there's one area that I don't know a good amount about on a car it's water pumps. I have just always assumed that the more blades the more water it'd move but after lilcuda's comments I wonder if I have been mistaken all along. I just checked the FedEx tracking and mine is scheduled to be here today and hopefully it's a 8 blade as I have the 6 blade they sent me here to compare it with. What lilcuda says about a 6 vane possibly moving more water due to larger vanes makes sense. If they weren't such an odd shape I could figure the area easy. I think more blade area would equal more flow?? My application is different than yours as I don't have A/C. I have the March under drive pulley's so that was my reason to think I needed a pump with more blades to move more water since it's running slower and mine runs a little warm in the summer. If you can't find a 8 blade an old trick to help prevent cavitation I've heard is to run one of the Flowcooler (I think that's the brand but I might be wrong) discs that rivets to the back side of the blades and encloses them. It's also supposed to help it pump more. I bought one from Summit a few yrs. ago but just looked and I don't see it listed now.

Maybe Lilcuda has a comment on whether or not he thinks it would help with cavitation.
 
In 40 years of working on engines, I have never seen cavitation effects on a water pump impeller. It is unlikely that you can spin one fast enough on the average engine to cause cavitation.

The factory did speed the fan drive up a little in A/C cars. Not a lot compared to some other manufacturers, but some.

The redesigned pump housing will have a lot more to do with the flow capacity of the pump than the blade count. Reducing the impeller to housing clearance of this type of pump has a dramatic effect on performance. Modern manufacturing methods make it very easy to produce more precise parts.

Post picture of the changes that you can see in the newer part, and the older part you think is better.

.
 
Well I got my 8 blade pump today and I don't like the looks of it for 2 reasons.

1. the impeller is pressed on so far it will have a huge gap between it and the timing cover so I don't know how it'd ever flow good.

2. for some odd reason the bolt holes which should be 3/8" (+ maybe a few thousandths) are big enough that a 1/2" bolt will nearly go through them. That leaves a minor amount of room between the edge of the pump and bolt hole for sealing. When installed and the bolts nearly pulled up you can move the pump around quite a bit so I don't think it'll hold a seal. The 6 blade pump is not like this. It's bolt holes are 3/8" and because of that it has a lot more room around the edge sealing surface.

The blades are quite a bit bigger too so I think it'll flow better and is the one I'll use.

The 8 blade pump has one positive note. It looks like it's a heavier duty unit with bigger bearings.

I'll take some pics tomorrow and post them if I can find the time.
 
i use a 6 blade pump, with ac pullies. no problems with anything cooling relsted. granted, im pretty far fom stock these days.
 
I was going to use the six blade but the 8 came in today. It looks the same as the one I pulled off. It is a Cardone Part # : 55-33118. So Im going with it. As you can see in the picture the new one is visibly deeper. Bolt holes measure same with caliper and width and depth of blade sightly larger.

Thanks Craig
 

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The depth of the cavity behind the impeller is not important in this case. that is the intake side, and with that open impeller design you can't pull much head anyway.

What is more important is the clearance between the blades & the cast housing. The closer they fit the better. This allows it to produce pressure at the tip.

The next trouble spot is the open design of the impeller. to work well it needs to sit close to the surface behind it in the timing chain cover. Again, the closer it fits, the more effective it is at pumping.

Those two things you have some control over. The final thing that determines pump performance is the ratio between the outside diameter of the impeller, and the diameter of the intake bowl.

Do you have a picture of the dreaded 6 blade pump to compare?

Before you install that pump, measure the clearance between the blades & the pump casting.

Then measure the hang out from the gasket face to the back surface of the impeller.

Then measure the depth of the impeller cavity in the timing cover from the gasket surface. Or use a bit of modeling clay, and trial fit the pump with no gasket.

whatever method of measurement, what is the net clearance of the impeller?

B.

.
 
my5thmopar said:
I was going to use the six blade but the 8 came in today. It looks the same as the one I pulled off. It is a Cardone Part # : 55-33118. So Im going with it. As you can see in the picture the new one is visibly deeper. Bolt holes measure same with caliper and width and depth of blade sightly larger.

Thanks Craig
Click to expand...
I work at O'reilly and they should have been able to get that pump. We stock A1 Cardone at our store. The part number shows up on the web page also.
 
B thanks for the engineering comments, I'm guessing the designers know what the're doing. The net clearance is roughly .322. Not sure I got measurements correct.

440, It was special order from O.
 
Sorry I never got pics up yet comparing the 2 I have. The batteries died in my camera and then I came down with a real nasty cold so I just haven't been able to get around to it. I'll try to get them tomorrow. I'm interested to hear what bohica says about that much gap. I've always liked to see them have no more than 1/8" gap.

5th did you take account for the thickness of the gasket when you came up with .322?
 
my5thmopar said:
I was going to use the six blade but the 8 came in today. It looks the same as the one I pulled off. It is a Cardone Part # : 55-33118. So Im going with it. As you can see in the picture the new one is visibly deeper. Bolt holes measure same with caliper and width and depth of blade sightly larger.

Thanks Craig
Click to expand...

I like the looks of this pump. I read about too many over heating issues right here on FABO to even consider a 6 impeller pump. There is a big hunt for fan shrouds here on FABO every summer because of over heating issues.

Just because China thinks it is better that don't make it so. It just means they can make it fit more applications with fewer parts.
 
Guess I'll chime in. Back in the day (early '70's), the hot tip of the day with the 273 engines that ran a little hot, was to use the A/C pump from a 318/340 because it only had six blades, and moved more water. Blade spacing or something like that, and this was in, I don't remember, Hot Rod, Car Craft, Popular Hot Rodding,........somewhere.

I did it on my iittle 273 .060 and damn, it worked. Dropped by 20 degrees or so.

Russ.
 
Double M said:
Guess I'll chime in. Back in the day (early '70's), the hot tip of the day with the 273 engines that ran a little hot, was to use the A/C pump from a 318/340 because it only had six blades, and moved more water. Blade spacing or something like that, and this was in, I don't remember, Hot Rod, Car Craft, Popular Hot Rodding,........somewhere.

I did it on my iittle 273 .060 and damn, it worked. Dropped by 20 degrees or so.

Russ.
Click to expand...

From the factory A/C cars used pumps with 8 blades and non A/C used 6 blades. At least that is what my original factory Mopar parts manual shows.
 
Wow. At .300+ net clearance, that is more of a stirring device than a pump.

With all of the intake uncovered on the back side, it should fit closer to the backplane than that. If this was an oldsmobile we would be welding a cover on the back of that impeller.

On a 385 block ford I would be looking for .050 to .100 total net clearance with the gasket. That would be split evenly between the front & rear of the impeller.

This is one of those times I just scratch my head and wonder if it has always looked like that. The last 318 I owned I bought new in 1973, and I never had the water pump off of it (great engine, lousy body). I am not going to tear the 318 in my Barracuda apart to measure it, but I do wonder if it has that much clearance. I think I will measure the differential pressure when I get a chance.

As for pump designs, you really should not be able to look in to the inlet bowl from the back of the impeller like that, unless the cover fits very close to the back of the impeller. Take a look at a later mopar pump, like the ones that run in reverse on a serpentine belt. Or look at the pump for a 4.0 Jeep. Or several other examples. Solid back impellers have replaced the folded impeller in many makes & models too.

The stack up of tolerances as various manufacturers make parts from different tools, reverse engineer stuff etc. can be vexing. This may be the case here, or perhaps it has always been this way. It would not be the first time I saw something mopar and asked myself how they got away with that.

If anybody has a 20+ year old pump and /or front cover they can measure that would be great. Since we know the net clearance on this new pump, how does it compare to the old one? And how well did the old one cool?

I asked in another thread for any available pulley measurements on A/C vs non-A/C cars. If you have a factory A/C car I would like to know the drive ratio for the water pump / fan assembly.

B.
 
I have a NOS 68 model 8 blade A/C pump but no accurate way to measure it. Maybe I can see if I can get it measured if no one comes in with the numbers.
 
Oklacarcollecto said:
From the factory A/C cars used pumps with 8 blades and non A/C used 6 blades. At least that is what my original factory Mopar parts manual shows.
Click to expand...

When I posted what I posted, I was going from memory. But with your post, I thought I'd check.

I didn't post what was in a factory service manual, but what I remembered reading somewhere around 1972 or so. However, I have a Factory 1970 Dodge Challenger/Dart service manual on my desk right now, and on page 7-10, towards the bottom of the page, it says 318/340 standard pump blades 4.38" - 8, Air Conditioning 3.70" - 6.

I guess my CRS isn't as bad as I thought.

Russ.
 
Whoa! Maybe I got this wrong. I understand a little more of what B was asking. I have mic(s), caliper, depth gauges etc. Let me re-measure this again and I’ll give specifics on where and how. I’ll take some pictures.
So I’ll clarify what B asked for.

“Before you install that pump, measure the clearance between the blades & the pump casting.” You mean the "front" towards the hole, between impeller front edge/face and case, correct? It is going to be tough on the leading edge. I’ll try the depth gauge on the caliper or clay. Underside of impeller to casting .718 (old .623)and lead edge to casting .141 (old .078.

“Then measure the hang out from the gasket face to the back surface of the impeller.” OK I think I got ya here, impeller does hang out. Impeller width 3.594 old 3.614 I might not have subtracted this from total. Hang out is .045 (old .023)

“Then measure the depth of the impeller cavity in the timing cover from the gasket surface. Or use a bit of modeling clay, and trial fit the pump with no gasket.” About this…you’re looking for the front of impeller blade to the surface of the timing cover (water area). Ok I get the clay idea. I’ll squish it and then measure gasket separately since it will be added. Measured all 8 impellers face to cover face is .302 (old .299) Gasket is .030 (old unk) So having remeasured I still get .332 or an additional .001 Old one reads Japan GMB 19164-30 cooled jut fine.

Thanks Craig
 
I took some pics and measurements on the 2 new pumps I have. One is a 6 blade and the other a 8 blade. Here's what I saw

Impeller size 8- blade 3.59" dia x.71"high.....6-blade 3.85 dia"x.82" high

Using a straight edge I measured the amount the impeller sticks out the back of the pump casting. The 8 blade sticks out .080" and the 6 blade sticks out .23". HUGE difference but you'll notice in the pics that it looks like they got a little crazy pressing the 8 blade impeller on which made it worse. Yet at the same time if it weren't pressed on so far there would have been a much larger gap between the impeller fins and water pump cavity. Speaking of the fin to water pump cavity distance, I forgot to measure it but they look very similar. My car is put together and I don't have an extra timing cover to see how deep the cavity is but I'm sure the 8 blade won't even hardly protrude into it because of the thickness of the gasket. I would think due to that the 8 blade pump wouldn't cool very good.

I also did my best to measure the cavity diameter and depth in front of the impeller. The diameter on both was 3.0" but the 8 blade pump has a much shallower cavity at 2.25" vs. 2.88" for the 6 blade. I'm not sure what effect this would have on things???

Not only did the 6 blade pump have a larger diameter impeller but the milled area in the pump where it spins is slightly smaller than on the 8 blade pump so there is much less gap around the impeller fins to the pump casting.

Based on what I see my 6 blade pump would pump more water even in spite of it having 2 less fins.

One last thing, the 8 blade pump has a much larger diameter front bearing making it appear heavier duty. Probably due to the factory spinning it faster. The rear bearings look the same but it was impossible to get into them to measure them to verify that.
 
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