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Hey Guys I got a Milodon High Volume water pump to put on my 84 H/O. Then I was reading the book How to Build Max Performance Olds engines and he says not to use HV pumps because normal ones are plenty. So I also picked up an A/C Delco pump. Now the one on the car has the fan covered with a plate like the Milodon, and the new AC has an open impeller. I'm not trying to be picky just looking to use the correct one and maybe save a few bucks. I found a place that list a a Vin9 specific pump I could order that one too. Thanks Jackson
The A/C or heavy duty cooling option have the closed impeller pump like your 307 HO. I like the closed impeller best but make sure whatever pump you decide on is the correct length.
Last edited by olds 307 and 403; Mar 28, 2024 at 07:04 PM.
The cast closed impeller was used by Olds on the original pumps and it supposedly works better than the open stamped steel impeller pumps. With that said, I drive in 110+ summer temps with a parts store open stamped impeller and the engine runs right at the thermostat temperature. So my take is the open stamped impeller moves a sufficient amount of water, and you should focus on the rest of the cooling system (mainly the radiator) to ensure adequate cooling.
The GM p/n callout for the V08 HD cooling water pump is 556283 from as far back as 1975 at least for Olds V8. Casting # 412265. They came from the factory with a closed impeller from every factory VIN 9 water pump I've ever removed. However, OTC new pumps under the same p/n were built with EITHER ONE. I know, I've seen it with my own eyes. I have both versions on hand. Which sorta makes me suspicious that GM was having water pumps rebuilt and putting whatever impeller was available and passing them off as new?
TBH, I don't think it really matters all that much.
Fun71 is correct. I have used open steel impellers and held perfect temps.
This is a little controversial as most think the closed cast impellers work better. Thinking they decrease cavitation and have better cooling abilities..blah..blah.. blah.
I have sold many OEM Waterpumps and it's always the same ?. Does it have the original cast closed impeller ? A lot of the pumps I sell I give the option to send them directly to Mike (the Waterpump Man) to save them time and money. I have had lengthy conversations with Mike over this very same subject. He also believes the open steel impellers are just fine and may infact cool better. This is a man that many of us use and have come to trust for our rebuilds.
People seem to get hung up on this when in fact you may be doing yourself an injustice by using the cast closed impeller.
Why ? Because it's original ! WHO CARES ! It's inside the pump and can't be seen. More important is the housing casting #'s and date.
You rebuild Heads and Motors with modern internals don't you !
Below is a picture of an NOS Olds GM performance Aluminum Waterpump. This pump was engineered and built by the performance division of Olds in the early 80's for use in NASCAR. Original versions had no provisions for water in/out. Shortly after use in NASCAR they were made available through the performance catalog with water nipple threads.
NOTICE the open steel impeller.
Why do you think they engineered it this way. Especially for the beating they take in NASCAR.
Because they didn't know what they were doing or they wanted a change.... I don't think so !
Fun71 is correct. I have used open steel impellers and held perfect temps.
This is a little controversial as most think the closed cast impellers work better. Thinking they decrease cavitation and have better cooling abilities..blah..blah.. blah.
I have sold many OEM Waterpumps and it's always the same ?. Does it have the original cast closed impeller ? A lot of the pumps I sell I give the option to send them directly to Mike (the Waterpump Man) to save them time and money. I have had lengthy conversations with Mike over this very same subject. He also believes the open steel impellers are just fine and may infact cool better. This is a man that many of us use and have come to trust for our rebuilds.
People seem to get hung up on this when in fact you may be doing yourself an injustice by using the cast closed impeller.
Why ? Because it's original ! WHO CARES ! It's inside the pump and can't be seen. More important is the housing casting #'s and date.
You rebuild Heads and Motors with modern internals don't you !
Below is a picture of an NOS Olds GM performance Aluminum Waterpump. This pump was engineered and built by the performance division of Olds in the early 80's for use in NASCAR. Original versions had no provisions for water in/out. Shortly after use in NASCAR they were made available through the performance catalog with water nipple threads.
NOTICE the open steel impeller.
Why do you think they engineered it this way. Especially for the beating they take in NASCAR.
Because they didn't know what they were doing or they wanted a change.... I don't think so !
Your observations can also be taken the other way.
Why do you think GM engineered the closed impellers for the factory units? Because they didn't know what they were doing? The engineering competence question can go both ways. The open impeller OEM units have a pretty beefy set of blades on them anyway. I'd be more hesitant about a rebuilder using something more flimsy or more prone to corrosion/wear material-wise.
I'm not a believer of any of it because the clearances aren't exact enough to worry about closed vs. open impeller anyway. I haven't seen any pump curves on the pumps or any comparison tests, so no real evidence supports either belief for me. As long as you're not cavitating, you should be fine. JMO.
