Water pumps - when/how do you get cavitation?

[wheming]

Common block 2.5, reverse rotating water pump. Discussion related to issues being observed with MeanMini. But, since this is puzzling, i figured i would fish a bit.

Question: when and how would you expect to get water pump cavitation?
High rpm? High coolant temp & high rpm?

My understanding is Cavitation is mainly caused when at the pump suction, the pressure is lower than the flash point at the given temp. The fluid vaporizes, all or partly and you get vapor at the pump suction and passing through the pump.

Question 2: Does cleaning up the waterpump housing, smoothing the casting, and removing casting flash in the volute and discharge section of the pump, smoothing the angle at the top, etc. have an effect on the pumps likeliness to cavitate?

Question 3: Is the Ed Peters suggested mod of removing every-other blade of the pump impellar only for the early waterpump? Or applicable to the later common block reverse rotating pump? - The impellars are quite different.

Thanks for any insight and discussion.

[GLHNSLHT2]

Wayne, it's pretty easy to just swap on an early pump with a heavily ported housing and 3 fins ground down to see if that fixes your issue. :) While it's off I'd notch the oil pan to give you clearance if you have to take the pan off but don't want to remove the water pump. the 2.5 tall deck pans had this notch. And the Masi 16v's used the older pump but the newer CB and pan and they did a crappy job notching the pans but it works.

My recollection of the cavitation happening was around 3000rpms. Now this is off memory of things that were written either on the SDML or the FMPML way back in the day.


Ok did some digging on thedodgegarage and found this from 5digits

WATER PUMP: Why was the water pump rotation reversed?? A couple of reasons...

The single most important one is that it allowed for a larger impeller to be used. This raises the water pump efficiency at lower engine speeds. Water pumps are primarily designed for peak efficiency at low speeds, to generate enough/greater flow for engine cooling. The downside of this is that a larger impeller will cavitate earlier, at higher speeds. In some previous posts I have mentioned going to the older style pump, for this reason. This can really be found useful in DOHC/Lotus applications. The fan may cycle more at low speed BUT a gain in engine cooling, at high RPM, can be achieved. Owners of later model vehicles may notice that 3rd or 4th gear operation, on the highway, may yield a much higher engine temp. This is regardless of cool ambient temperatures. Utilizing the older style pump will basically achieve what an under drive pulley kit does.

Previous post on water pumps-

If you are willing:
Going to the old L-body water pump will help. The impeller disk is smaller in diameter,thus lowering tip speed. This will reduce the risk of cavitation at high RPM, without going to an under-drive system. This will help most applications, including DOHC engines. Although, the DOHC requires additional mod's.

NOTE: Mod's will/may include: Welding on an additional nipple, for heater hose connection. Fabricating an alternator bracket. All depends on the application.

[wheming]

Thanks Jay. This is interesting because i don't remember seeing alot of discussion from the really fast crowd about this. There are plenty of high hp and fast 2.2/2.5 out there that are common block cars. Are folks doing some other mods to their pumps or impellars?

Mini did have an underdrive pulley previously, but we went back with a stock one because of issues with low voltage at idle. It is a possibility to go back if that would be better. I need a good balance between daily street driving and dragracing in the configuration.

[mopar-tech]

568985689956900

Reliant runs an underdrive pulley and some minor porting in the housing but stock impeller.

I run the early pump, never cared for the later one running off the back of the belt.

Daytona ran the stock 89 CB setup with an underdrive pulley, never gave me any issues.

[shadow88]

Let's say if the coolant entering the water pump is nearing boiling (212f) and the low pressure area at the inlet wasn't under normal pressure like the entire cooling system is, I would think the only way that cavitation could happen is if the radiator is completely not up the the task it's made to do.

[wheming]

I never seen any overheating, and don't see temp even go over 200 normally, since i have the fan come on early. That's what doesn't make sense to me. If the pump was starving at the suction, then maybe?
The other thought i had was, what if there was excessive clearance between the impellar and the housing? Is there a spec clearance if someone wanted to blueprint their water pump?

[wheming]

56898[

Reliant runs an underdrive pulley and some minor porting in the housing but stock impeller.

I run the early pump, never cared for the later one running off the back of the belt.

Daytona ran the stock 89 CB setup with an underdrive pulley, never gave me any issues.

Gary, what are the fittings at the top of the pump discharge used for?

[4 l-bodies]

Wayne,
For what it is worth, I use early pumps on all performance enhanced motors whether they be early block, common block, SOHC or DOHC. My housings are always fully ported and most of the time have crank underdrive pulley. I do not remove any impellers (per Ed Peters suggestion). I also have pressurized coolant from waterpump outlet feeding the #4 core plug with a 3/8" hard line, as well as the core plug in head (ASA's fitting) removing coolant from #4 chamber. I do not have coolant issues at all. My belief is the pump needs to be moving coolant somewhere, whether it is at idle RPM, or WOT & 7K, or whether thermostat is open or closed, otherwise cavitation can occur.
I used to watch many vehicles on the chassis dyno and their water temps would simulate the RPM on the tach during a pull. Dyno operators I know say they see this all the time.
Todd

[Force Fed Mopar]

Hmm, I wonder if this is why I've always had overheating issues in the Lebaron on mountain runs. I've never, ever had a problem with it on interstate runs, even when pulling WOT all the way from 2nd gear to the speed limiter in 5th (120mph currently). But after 10 mins of running in the mountains, it's starting to get hot, and will climb to 3/4 gauge if I keep pushing it. Speeds are obviously slower in the mountains but still moving 30-60mph. Could be the radiator possibly, but my old GLHS had the same rad (full-width single-core V6 rad) and never gave me a problem. Granted it was a lighter car, but it also had a non-CB bored .030" and the early style pump. Lebaron has a 2.5 CB bored .040" and the newer CB water pump. Neither had a ported housing. Both stock swirl heads (in fact, Lebaron is using the same exact head lol). Both 2-piece intake, stock turbo, 3" exhaust, etc etc.

[wheming]

Todd, do you have any pics of that pump discharge line to the #4 block plug? I don't think I've seen that before.
The suggestions you made, and the notable history of several builds like this are encouraging.

I'm not sure yet which direction we'll go. I do have Asa's mod on the head, and it is setup to go to the heater valve, which normally bypasses back to the pump.

What size is your fitting on your Asa kit?

[mopar-tech]

56911569125691356914
Gary, what are the fittings at the top of the pump discharge used for?

As the power level rose I had issues with the headgasket going out on the back of cylinder one and the front of cylinder three.

Note- This is with the coolant mod "t-stat" relocated on the back of the head.

So I simply fed cool coolant to these locations right off the water pump.

[4 l-bodies]

Wayne,
Here is a pic of coolant hard line. I made three core plugs up, 1) 3/8 NPT to 45° flare, 2) #3/8" to -6 AN fitting, 3) 3/8' NPT to 3/8" hose barb. This is obviously #1. Steel plug with fitting brazed.
My ASA # 4 was tapped originally 3/8" NPT. I was going to re-drill and tap for 1/2' NPT but haven't done that yet.
Todd

[4 l-bodies]

...I do have Asa's mod on the head, and it is setup to go to the heater valve, which normally bypasses back to the pump.

What size is your fitting on your Asa kit?

Wayne,
If I didn't retain the factory hard line running to heater core (see pic previous post), I would have re-drilled and tapped ASA fitting for 1/2" NPT if I were going to feed heater core with it. Then use 1/2" to 5/8" hose end fitting.
Todd

[wheming]

Thanks Todd.
That looks pretty slick. I can't remember seeing that before. Very neatly executed.

My Asa #4 is unmodified from how he packaged it, but i'm thinking to upsize that fitting.

I'll have to discuss this with Brian. I think i have some 3/8 SS tube as scrap. Might even have some Swagelock fittings

[wheming]

Oh, and have you changed the alternator pulley with your underdrive crank pulley?

[4 l-bodies]

Oh, and have you changed the alternator pulley with your underdrive crank pulley?
I run a 90 amp ND alt. with shortened early block lower alt. bracket. This is really only helpful in cramped L-body engine bay. The 90 amp seems to be okay at idle, but the original 6? amp L-body alt. didn't like the under drive crank pulley. Those original l-body alts are like the first thing I change every time I buy a new L-body.
Todd

[wheming]

I run a 90 amp ND alt. with shortened early block lower alt. bracket. This is really only helpful in cramped L-body engine bay. The 90 amp seems to be okay at idle, but the original 6? amp L-body alt. didn't like the under drive crank pulley. Those original l-body alts are like the first thing I change every time I buy a new L-body.
Todd

Ok, thanks Todd. I know i visited this once before when i was first starting Mini's restoration. I seem to think i already had the higher amp alt. But with headlights, rad fan, and heater blower on with the underdrive i was negative every time at idle.
Someone had posted to me the part number for a different alt pulley, can't remember the application, maybe some mazda or something.

I know i can bump my idle target a bit, and that wouldn't necessarily be bad, but don't know what it would need to be to always stay positive without some testing. I'd rather have a pulley change, and not have to worry though.

Also, I do have an A/C bracket though i need to work around with these changes to the cooling system or with a different alt.