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1978 w150 318 727
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Discussion Starter · #1 ·
I have a 1978 w150 318 with factory a/c. We removed the radiator and have a new one on the way. I scoped the water pump from the inlet port and counted 8 fins, its a non high performance pump with an open impeller design. There is currently nothing wrong with the water pump, no leaks and the fins seem fine and intact.

However upon doing some research I found that vehicles with factory a/c were suppose to get 6 fin water pumps and non a/c got 8 fin water pumps.????? My question is if this is the case do I go to the extent of changing the water pump or will the 8 fin be fine? The original part number for the 6 fin is 3837641, the 8 fin is 3780109.

I did see that replacement water pump  #4728533 takes the place of both of the parts numbers above and from what I can tell is its a 6 blade water pump.

Should I change it out just to have the 6 fin or should I leave it alone??

It was running hot but the radiator was completely clogged.

I am getting mixed stories on the 6 fin vs 8 fin and which one was suppose to be on a/c or not.
Any suggestions would be great.
Thanks
D
 

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over the years I've seen both , run both with no problem . You don't say why your concerned other than some info you found , is there a problem ? if not , don't create one , if its not broke there IS nothing to fix there .  Sounds like your addressing THE problem with an unclogged radiator ....  ;D
 

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Discussion Starter · #3 ·
Other than it was just running hot before, but yes the radiator was most likely the problem.  Wanted to just make sure I would be getting adequate flow with the a/c since I am in AZ just north of hell Temps.

But I also just realized we took the radiator out 6 days ago and the system has been sitting dry. Now I am concerned with seals and gaskets drying out in this 110 dry heat. Probably just caused a whole nother issue.
 

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Discussion Starter · #5 ·
I went ahead and plugged the bottom of the water pump and filled it up with antifreeze just in case. It's a really dry heat here.
 

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;D ;D ;D ;D ;D yer worryin too much ........... the graphite seal will be fine the paper gaskets are "contained" squashed between the metal ,started life dry as a bone , and are so squished they are still that way .  ;)
 

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Agreed, the seal on the pump shaft, is likely a ceramic, or carbon seal. As long as it is not run while dry, it will stay forever.
 

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Discussion Starter · #8 ·
Oh I know I am worrying too much, that's what I do. Ha. I am a pool guy in AZ and when 2008 hit tons of Pools here were left for dead. When we would start them back up the seals on the pumps were always bad. They are exactly the same as what's on a water pump. It's the rubber part of the seal that dries out and cracks while it's shrinking and there ya go. But was just checking with yall. Thanks for the advise. I take it the 8 blades on the water pump is fine and will just replace it if it ever goes bad with the correct one.
 

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Must be chinese pumps, or seals. I rebuild irrigation pumps as a side job here, I won't touch anything listed as hot tub, or pool, or anything with plastic. Red lion pumps look good on the outside, but they have plastic innards. Run them dry for a minute, and the plastic volute will warp, and melt. As you mention, the rubber around the seal, will quickly melt, and then leak. What I have found, is it is all from running dry, as there is nothing to remove the heat generated by the carbon side of the seal.

As far as the 6 vs  8. It seems chrysler decided the difference was not worth the hassle of having two. I think there is more to the two designs, then the number of blades. I have seen differences in the center hols that feeds the water from the lower hose, and the bypass. I have also seen a difference in the blade design. some go straight out from the center shaft, others are offset, giving them a slight spiral effect. How many of those are aftermarket, vs Mopar, I cannot say. I have studied water pump design, and even the experts cannot agree on impeller design, and even the number of vanes. I think the path for the water going into the impeller, and the volute design are bigger factors.

Also, remember the AC engines turn the water pump faster then the non AC, by way of the different pulley sizes. Toss in the 5 or 6 blade fan and shroud, vs the 4 blade fan  and often no shroud, and you have so many outside factors, that there is no way for anyone outside a lab to say whats nest, or even better.

My recommendation is to go with the performance pumps with the backing plate, a 5 or 6 blade fan, and an extreme duty clutch, and a tight fitting shroud.

 

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Discussion Starter · #10 ·
All very good information. I agree with the volute design. Back in the day when pool pumps were brass it was critical that the impeller was adjusted as far forward to the volute with out touching in order to maximize flow. Then came along the closed faced impeller ridding any need of adjustment. I was and am looking for a 20 inch 5 blade fan for my 22 inch shroud. I have a oem fixed 5 blade right now. But it takes forever for it to warm up in the winter. If you have any suggestions on what fan blade part number to use that would be great.

I can only find a heavy duty Hayden 2747 clutch. I haven't seen an extreme duty that will fit.

I will keep the 8 fin water pump.
Thanks for the info.
D
 

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HAYDEN 2797. Sorry, its severe duty, not extreme. Don't understand why Rock auto does not show it for 70's and 80's trucks.

As far as the fan, I plan to hit up the junk yard, with a ruler and look for the best I can find. Then I will make a shroud to fit the fan. Too bad the magnum engines rotate the pump backwards, they have great fans, and pumps.
 

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daryl78powerwagon said:
Oh I know I am worrying too much, that's what I do. Ha. I am a pool guy in AZ and when 2008 hit tons of Pools here were left for dead. When we would start them back up the seals on the pumps were always bad. They are exactly the same as what's on a water pump. It's the rubber part of the seal that dries out and cracks while it's shrinking and there ya go. But was just checking with yall. Thanks for the advise. I take it the 8 blades on the water pump is fine and will just replace it if it ever goes bad with the correct one.
chlorine or whatever ya call the corrosive stuff you put in pools , and the cheap rubber deals on those pumps , yeah liquid transfer , and my spa use them , your right they leak , auto w/p's are a tad different .. ;)
 

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Discussion Starter · #13 ·
I found what the concern was of the fin count. The 8 fin with the a/c pulley supposedly can cavitate at freeway speeds. If that explains any concern I was having.

As far as the fan blade, I saw in the 78 part book a 20 inch 7 blade 3462149 that will take a fan clutch otherwise the 5 blade that will take a clutch for those years is only an 18 inch. Wondering if I can just use the 20 inch 7 blade?
 

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Discussion Starter · #14 ·
I found a 5 blade 20 inch fan blade for various trucks 82-91 part # 4266059. This possibly could work for what I need. Thinking this one or the 7 blade 3462149. Either one I think will work. If anything I could switch the 5 blade seasonally if I need to.
 

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Cavitation is a result of blade design, and speed. Blade count will not make a difference. A flat blade itself will have cavitation, but there is no trailing edge fro the cavitation to act on, so it ends up being a vacuum bubble following the back side of the blade. I could see a bubble pocket bridging the blades, with the closer design of the 8 blade, but if that was an issue, then Mopar would not have gone with the 8 blade design for all small blocks like they did in the 80's. The main thing you get with a blade count change, is a change on pressure pulsations, Which I think are dampened from the open style volute. I would love to see someone take all the good points of the magnum pump, and change the blade angle for regular rotation, for the older LA engines.

As far as fan blades, I would not worry about any particular one, just hit up the junk yard until you find one that turns right,and the right diameter. Dodge, cheby, toyota, does not matter, they are just a fan.
 

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Discussion Starter · #16 ·
I will have to hit up ebay for the fan, our junkyards in Phoenix don't go past late 90s. At that point most of the fans are the single giant nut design. Unfortunately the old stuff doesn't move fast enough for them to keep the oooolldd ones in the yard. But at least that opens me up to more models or readily avaible fans. Dodge is hard to come by. That make sense though cause I did notice the clutch fits almost every make all the way into the 90s.

Radiator showed up today from kks, part number KKS889. Wow this thing is stout. Very impressed with the construction. Bummer the mail man smashed in the side. New one is on the way. But really nice solid aluminum radiator for only $265. Can't wait to see how well it cools.

Thanks for
 

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That radiator does look good. This place is almost a junk yard desert. All the insurance wrecks get towed to Denver.
 

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Discussion Starter · #18 ·
We have tons and tons of junkyards but when you call asking for a 1978 anything they laugh and say no dude we haven't had that kinda stuff for 15 years. Thank God for ebay or I wouldn't find much if anything.
 

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Maybe it is because I spot then, but there is lots of old Dodges driving around here. Don't see as many old chebys, and fewer fords. But see a handful of old scouts, and travelalls. There is a big yard here that has lots of old stuff, but they think it is all solid gold. Neighbors do not like it, but my main stock is scarfing up good deals on Craigs list.
 

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Discussion Starter · #20 ·
Going to go with this setup. KKS889 radiator 3 row, derale 17120 20 inch 6 blade fan and Hayden 2797 severe duty fan clutch. This should get the job done. Hopefully with this the a/c will still work good at adle and I won't have to add an electric condenser fan. That would keep me from having to upgrade the alternator hopefully.
 
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