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Parts stores not stocking the 6 vane waters pumps for the a/c cars.

GMP440

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Looking to replace the water pump that's in my 68 Coronet with 318 and a/c. Autozone, Napa, Advance, Orelley's have the 8 vane pumps for the non a/c cars and not the 6 vane pumps for the a/c cars.
Is this an issue where the pump manufacturers are just manufacturing one pump style to be used for a/c and non a/c cars? Will there be any cooling issues using an 8 vane pump on an a/c car?
Who has the correct 6 vane pumps?
 
Airtex Aw919 is a 8 vane. The application says non a/c but it has the 8 vein impeller in it.

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Yes, the OP is aware that there are 8 vane pumps for non a/c cars. He is looking for a 6 vane designed "for" a/c cars.
Boy I messed that one up. I had a few 6 vein pumps up. It's a pain opening each description and going through photos to find the backside view. And all just to help a member. Yes @GMP440, I saw a couple 6 vein pumps on Rockauto's site. They looked like the same pump and they were brands I have never seen before. You can check it out yourself. Good luck.
 
IMO.....Why not just use the 8 vane pump? The worst thing that MAY occur is the circulated coolant velocity will be higher, which is a good thing, as it promotes better heat exchange efficiency. There were 2 pump variations for the B/RB engine, the 6 vane pump was used with A/C because of the water pump drive ratio was significantly higher than the 8 vane pump used a slower water pump drive ratio. I am not aware that the LA 318 with A/C uses a different water pump drive ratio or water pumps with different impeller vane compliment. My advice, use the 8 vane impeller pump. Just my opinion of course.
BOB RENTON
 
It wouldn't be a bad idea to make sure that your lower radiator hose has a spring in it . To prevent it from collapsing with that 8 vaned pump.......
 
Here's your references for the different cooling applications. It's a little blurry but zoom in and you can see them.

Screenshot_20220427-074318_Chrome.jpg
 
IMO.....Why not just use the 8 vane pump? The worst thing that MAY occur is the circulated coolant velocity will be higher, which is a good thing, as it promotes better heat exchange efficiency. There were 2 pump variations for the B/RB engine, the 6 vane pump was used with A/C because of the water pump drive ratio was significantly higher than the 8 vane pump used a slower water pump drive ratio. I am not aware that the LA 318 with A/C uses a different water pump drive ratio or water pumps with different impeller vane compliment. My advice, use the 8 vane impeller pump. Just my opinion of course.
BOB RENTON
Someone here posted a chart. Good information. The fan/pully ratio is .95:1 for the non a/c cars that use the 8 blade vane pumps and 1.3:1 for the a/c cars using the 6 vane pumps. Whether or not the there will be a difference in cooling temps who knows. Just don't want to have issues of overheating in traffic with the 8 blade. Won't know until the pump is on and then going for a road test to see how it all goes.
 
Did you try the 8 vane pump? I don't think you have to worry about over heating with the 8 vane with the 1.3:1 pulley. You might have more noise/cavitation. I have an engineering theory on the differences between the two systems. It's a little confusing but I'll try my best to explain. First thing, my service manual shows different number for the 318 cars than posted above. My book list the same pulley ratios, however the pump diameter is a 10 blade 4.2" vs a 6 blade 3.5" for the AC cars. I'm going to use those numbers below.

Clearly the engineers wanted more volume for the AC cars, thus the 1.3:1 pulley. The problem this can cause is the tip speed of the vanes spin too fast and cause cavitation. That's likely why they reduced the diameter of the vanes for the AC cars. So, lets compare tip speeds for each at 1,000 rpm:

1.3:1 pulley with 3.5" vanes has a tip speed of ~ 14,294 inches per minute
.95 pulley with 4.2" vanes has a tip speed of ~ 12,534 inches per minute

if you have a 1.3 pulley with a 4.2" vanes the tip speed with be ~ 17,153 inches per minute

Okay, so as you can see that is likely why they reduced the diameter, to help reduce the risk of cavitation. But reducing the diameter also reduces the volume it can move, even with it spinning faster. So, to get the volume back up they removed blades which makes the pump take bigger bites and moving more per rpm, thus moving more liquid. So with all that said, if you are turning a 8 vane with the 1.3:1 pulley you will likely be moving more volume than you would with a 6 vane, however it may cause cavitation... Hopefully that makes sense and is helpful.
 
I'm watching this with interest and am going through this right now as well. I've installed a high flow high fin count Flowkooler pump to go with my non-A/C pump pulley. I don't have it all back together yet and have decided to install aftermarket A/C which has the smaller diameter AC water pump pulley. With the smaller diameter pump pulley and fast flowing Flowkooler pump, I could risk cavitation at higher RPM and I'm wondering if I should rip out the pump I just installed and re-install the Milodon 6 fin pump to match the smaller diameter A/C pulley. I'll share results either way and look forward to results from the OP also (knowing that everyone's engine combo can behave differently).
 
I'm watching this with interest and am going through this right now as well. I've installed a high flow high fin count Flowkooler pump to go with my non-A/C pump pulley. I don't have it all back together yet and have decided to install aftermarket A/C which has the smaller diameter AC water pump pulley. With the smaller diameter pump pulley and fast flowing Flowkooler pump, I could risk cavitation at higher RPM and I'm wondering if I should rip out the pump I just installed and re-install the Milodon 6 fin pump to match the smaller diameter A/C pulley. I'll share results either way and look forward to results from the OP also (knowing that everyone's engine combo can behave differently).
The only true way to determine pumping capabilities is to look at GALLONS / MINUTE flow rate at a specific RPM, not the number of fins or vanes. Typically, centrifugal pumps are rated at a GPM and pressure, at a steady or constant RPM. But, in automotive cooling systems, the pump RPM varies, therefore, the pump curve, or operating parameters must be broad enough to encompass, IMO, 75% of the coverall operating conditions. YES...these items determine the flow rate at a specific RPM and the flow pressure at which coolant is circulated. Wether there will be cavitation at the operating point is determined by the clearance from the front of the impeller to the pump housing (0.025" +/-) and if there is sufficient Net Positive Suction Head or NPSH at the impeller "eye" or the inlet pressure at the impeller. Because the system operates at a pressure determined by the radiator cap, typically 16# pressure, the POSSIBILITY of cavitation is low or likely zero. The specific gravity of the coolant also influences the pumping conditions and if any cavitation can occur.
Personally, I would use the Flowkooler pump installed with the the pump sheave ratio that provides the highest pump (and cooling fan) RPM to circulate the greatest VOLUME (GPM) and Speed (ft/sec) of the coolant to yield the best operating conditions and not worry about any cavitation possibilities. I would also use a 50-50 mix of ethylene glycol and water, without any additives. Remember that a "water wetter" compound is nothing more than an ionic surfactant which reduces the surface tension of the water, just like "FINISH" in your wife's dishwasher. Just my opinion of course....
BOB RENTON
 
The only true way to determine pumping capabilities is to look at GALLONS / MINUTE flow rate at a specific RPM, not the number of fins or vanes. Typically, centrifugal pumps are rated at a GPM and pressure, at a steady or constant RPM. But, in automotive cooling systems, the pump RPM varies, therefore, the pump curve, or operating parameters must be broad enough to encompass, IMO, 75% of the coverall operating conditions. YES...these items determine the flow rate at a specific RPM and the flow pressure at which coolant is circulated. Wether there will be cavitation at the operating point is determined by the clearance from the front of the impeller to the pump housing (0.025" +/-) and if there is sufficient Net Positive Suction Head or NPSH at the impeller "eye" or the inlet pressure at the impeller. Because the system operates at a pressure determined by the radiator cap, typically 16# pressure, the POSSIBILITY of cavitation is low or likely zero. The specific gravity of the coolant also influences the pumping conditions and if any cavitation can occur.
Personally, I would use the Flowkooler pump installed with the the pump sheave ratio that provides the highest pump (and cooling fan) RPM to circulate the greatest VOLUME (GPM) and Speed (ft/sec) of the coolant to yield the best operating conditions and not worry about any cavitation possibilities. I would also use a 50-50 mix of ethylene glycol and water, without any additives. Remember that a "water wetter" compound is nothing more than an ionic surfactant which reduces the surface tension of the water, just like "FINISH" in your wife's dishwasher. Just my opinion of course....
BOB RENTON
All great points Bob! Thanks for your insight.
The only way to know for sure with my setup is for me to try it and if any new higher RPM issues show up, I can always swap the other pump back in.
 
Hello everyone. Sorry I didn't report back sooner. I replaced the water pump. What I had on was a 6 vane pump. I replaced the pump with an 8 vane pump.
None of the parts stores and water pump manufacturers have the 6 vane water pumps for a/c cars.
Did alot of research on this. They all produce pumps for non a/c cars. Dayco; they list both a pump for a/c cars and one for non a/c cars. Both pictures in their parts catalog show both pumps being exactly the same with 8 vane impellers.
The pump bodies that are used are correct for an a/c equipped car. It has the bypass fitting and heater hose fitting. Next to the heater hose fitting the pump is recessed to accept the bracket for the R-V2 compressor and it has the 8 vane impeller.
I ran the car and it cools just as good as the 6 vane pump I had before. With the a/c on cooling is very good. Where the guage needle is sitting is where it always is and has been for as long as I had the car.
So, what's going on,the pump manufacturers are just producing 8 vane pumps that will work for a/c and non a/c cars.
I hope this helps others in this same dilemma.

Temp guage.jpg
 
Hello everyone. Sorry I didn't report back sooner. I replaced the water pump. What I had on was a 6 vane pump. I replaced the pump with an 8 vane pump.
None of the parts stores and water pump manufacturers have the 6 vane water pumps for a/c cars.
Did alot of research on this. They all produce pumps for non a/c cars. Dayco; they list both a pump for a/c cars and one for non a/c cars. Both pictures in their parts catalog show both pumps being exactly the same with 8 vane impellers.
The pump bodies that are used are correct for an a/c equipped car. It has the bypass fitting and heater hose fitting. Next to the heater hose fitting the pump is recessed to accept the bracket for the R-V2 compressor and it has the 8 vane impeller.
I ran the car and it cools just as good as the 6 vane pump I had before. With the a/c on cooling is very good. Where the guage needle is sitting is where it always is and has been for as long as I had the car.
So, what's going on,the pump manufacturers are just producing 8 vane pumps that will work for a/c and non a/c cars.
I hope this helps others in this same dilemma.

View attachment 1327193
Real world results! I'm surprised both cooled about the same. Is this at idle and all speeds? Thanks for sharing.
 
I've been running the eight blade since the beginning in my 440 non a/c. Never had any overheating issues, even on a hot day in stop and go traffic.
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