ST4s Water Pump Impeller aka WP Fan compatibility - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 11 (permalink) Old Jul 1st, 2019, 12:33 pm Thread Starter
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Question ST4s Water Pump Impeller aka WP Fan compatibility

I am hoping to draw on some Ducati parts experience to determine part compatibility of water pump impeller also referred to as a water pump fan in Ducati Parts manuals for replacement in my 2002 ST4s.
I have attempted cross reference via https://www.bike-parts-ducati.com/du...le/price/44700 but, I cannot determine the differences. I can however plainly see the different PNs.

Are the differences in impellers due to size or height of the impeller blades or shaft length / shaft diameter? Something else?
If blade height or diameter, could a corresponding water pump housing be used? i.e. pair an impeller from '03/04 with housing from '03/04 and install on '02 ST?

Of note, the Alternator/Generator cover is shown as 24220381BB superseded by PN 24221101A which is shown to fit every ST from 01 to 07 in addition to others.

Ultimately, I am hoping to get better coolant flow in my ST4s. Even if not realized, I also hope to gain knowledge on the differences or compatibility of the the water pumps impellers and housings for the ST series.

Thank you!
Vince



The PNs I am referencing are below:

Water Pump Impeller (fan):
2002 ST4s shows PN 25120024B -- actually 25120014B but is superseded by 25120024B (2001/2002 M S4, 2001 996 + 996S + 996R, 2001 ST2 +ST4, 2002 998 and 2002 ST4 +ST4s)
2003 ST4s shows PN 25120026B
2004 ST4s shows PN 25120026B

Water Pump Cover
2002 ST4s PN 24711141AB
2003 ST4s PN 24722021A
2004 ST4s PN 24722021A


Vinnie R.
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2004 998s FE
2002 ST4s
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post #2 of 11 (permalink) Old Jul 1st, 2019, 5:50 pm
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i think you'd need the alt cover as well. i do recall them changing stuff to make things bigger around 2003, but can't recall specifics. maybe it was 749/999 only?

why do you want it to flow more coolant?

know all wanker
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post #3 of 11 (permalink) Old Jul 2nd, 2019, 12:33 pm Thread Starter
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Hi Belter,

alternator cover is PN 24221101A which is shown to fit every ST from 01 to 07 in addition to others (998/996/748/S4/S4R)


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2004 998s FE
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post #4 of 11 (permalink) Old Jul 2nd, 2019, 3:19 pm
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Desmotimes used to sell a higher capacity fan blade with a manual switch kit so you can keep the fan on at your descretion. Should keep the temps down at idle for you.
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post #5 of 11 (permalink) Old Jul 2nd, 2019, 3:48 pm
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Yeah, there are easier ways to manage temps at idle and in traffic that don't include replacing water pump impeller... These bikes get hot in traffic and at idle, the manual fan switch and better fan blades are probably the most popular and easiest. Using something like Engine Ice as a coolant helps a bit too, but if there is no air moving across the radiator, they get hot fast.

Dan. "Painfully mistaking my big talk for the truth" Samantha Fish.
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post #6 of 11 (permalink) Old Jul 2nd, 2019, 5:16 pm Thread Starter
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made a mod and have dual fans, manually controlled, both with the Muzzy blades, running Engine Ice. (In the day, worked in same office w/brother Snyder at SOCOM) Anyway, ...running BOTH fans at idle in 90F, water temp holds around 220F

So, the question from the original post, specifically to discern the differences of the impellers from the various years STs. Ducati made a change (at least in PN) between 2002 and 2003 in the impeller and the water pump cover but NOT in the alternator cover.

Curious as to the differences in the impellers... "Are the differences in impellers due to size or height of the impeller blades or shaft length / shaft diameter? Something else?"

thanks


Vinnie R.
Tennessee

2004 998s FE
2002 ST4s

Last edited by grimah1w; Jul 2nd, 2019 at 5:20 pm. Reason: clarify purpose of the post...determine impeller differences
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post #7 of 11 (permalink) Old Jul 2nd, 2019, 8:50 pm
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Good question. Maybe some of our Ducati experts may know? Like Brad Black, Ducvet, etc?

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post #8 of 11 (permalink) Old Jul 3rd, 2019, 4:30 am
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Quote:
Originally Posted by grimah1w View Post
made a mod and have dual fans, manually controlled, both with the Muzzy blades, running Engine Ice. (In the day, worked in same office w/brother Snyder at SOCOM) Anyway, ...running BOTH fans at idle in 90F, water temp holds around 220F

So, the question from the original post, specifically to discern the differences of the impellers from the various years STs. Ducati made a change (at least in PN) between 2002 and 2003 in the impeller and the water pump cover but NOT in the alternator cover.

Curious as to the differences in the impellers... "Are the differences in impellers due to size or height of the impeller blades or shaft length / shaft diameter? Something else?"

thanks
Yikes. Two fans running? That does seem hot with two fans running. I have those temps in traffic with the one OEM fan running, but it comes down fast once moving again.

Can't help with the impeller question. Maybe it's time to go on an eBay fishing expedition and grab a few for comparison. Maybe there is a size or shape difference. Question is if it significant enough to make a difference in your situation.

Since you've gone to that extreme, I certainly assume you've made sure the radiator fins aren't packed up with bugs and gunk or blocked up internally.

Edit. Thinking about this. I have two bikes in the garage with DQ engines. The 1995 916 has a single phase generator and the 4 bolt water pump cover. The 2003 ST4s has the three phase generator and the 5 bolt cover, also it is in the model year range of parts you're looking at for as a possible improvement to your bike. The heating characteristics are pretty much identical between the two bikes. I am running OEM fans that come on at the OEM prescribe temp (210 ish) and both happily get to 220 ish while sitting miserably in traffic. Both bike's thermostats open around 150 and they settle in between 170 and 190 while moving depending on ambient temps. Running Engine Ice in both.

I too would expect lower temps with two fans running, but I've personally never tried it. Although it seems very hot, I'm not sure being at 220 when sitting at idle is really that big of a deal to the engine, to us yeah, it seems like a melt down is in progress. I'd hope Ducati would have designed the cooling system to prevent those temps if it was dangerous, but...

Dan. "Painfully mistaking my big talk for the truth" Samantha Fish.
2003 ST4s (The Truck)
1995 916 (Junk Yard Dog)

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post #9 of 11 (permalink) Old Jul 3rd, 2019, 11:12 am Thread Starter
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(Dan, What you describe is consistent with what I am seeing on my '02 ST4s.)

I have been quite diligent with the maintenance of the bike and have paid special attention to the cooling system including removing the radiator and straightening fins as necessary and of course keeping them clean of debris. It is hard to assess the internal condition of the radiator but, every two years it gets a flush with solution of water and vinegar, rinsed, then refilled with Engine Ice. A few years back replaced the thermostat (Ducati OEM), plus have replaced temp sending units and run SAMCO silicon hoses w/ their clamps.

I do not recall experiencing elevated coolant temps as now, when the bike was early in its life. I've lived in Savannah GA, middle TN and Tampa FL, had plenty of hot days in the summer, although I did and still do avoid city riding as much as possible. Like most of us in this discussion and on the ST forum, I know that these machines (and I) are happier when moving along briskly...when doing so I see coolant temps at about 187F while ambient temps are in the 70's to 80's; when ambient temps are higher 80's to 90's, 60-70ish MPH yields about 194F coolant temp, with variations based on throttle application. BTW, I have measured radiator temps at idle in my garage with a quality pyrometer and have verified my temp sending units.

The addition of the second fan and being able to activate both manually does have a pronounced effect on cooling at idle when I encounter elevated temps. When I am greater than 195 and know I am going to be crawling (less than 25 MPH) I activate the fans. When idling in traffic or at lights, with the fans on, at ambient temps of 80-90F my coolant temp reads about 220F, I cannot imagine what I'd see if I did not have the second fan and counted on one only and solely ECU controlled...I don't want to risk engine damage by experimenting to find out; like you say to me it seems way hotter than most road going ICEs. (it is notable that the temperatures and humidity are usually a bit higher here in Middle TN than say, Killington VT, Coventry CT, or Worcester MA Dan, thanks for sharing your observations on your 916 and '03 ST4s! Did they always behave that way, or has that become a new normal? To me, and I may just have a rose colored memory about it, it seems that with age the engine temps seem higher, despite the maintenance efforts.

I cannot help but speculate that Ducati made a change in the ST4s from '02 to '03 to the water pump impeller and housing for a reason...I hypothesize it was to improve the pump's flow but I cannot discern from photos on the web what the differences are. I am guessing that the fins may be taller and or maybe slightly greater in diameter, or that their shape was altered to produce better rate of circulation even at low engine RPM. Maybe they just got a new supplier with different tooling!!!

I've read Shazaam's informative writings on the design of the Ducati water cooling system and I understand and appreciate theory and application of the laws of thermodynamics. I am curious to know what Ducati changed and why in the water pump, and IF it was to improve low speed/low RPM engine cooling, I'd like see if I can apply it to my beloved '02 ST4s!

I may just break down a set of WP impeller and cover...will share what I find.

Thanks all for your interest and information.


Vince


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post #10 of 11 (permalink) Old Jul 3rd, 2019, 3:55 pm
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Vince.

I've owned my ST4s since May of 2005. Had just under 4K miles on it when I got it, well over 50K now. I lived in SE Virginia at the time and commuted daily with it for a few years before moving on to my current situation. I don't feel it was any different to be honest. I encountered more traffic back then. My commute was 50 miles one way. Much of it on the heavy traffic prone RT64 between Va Beach where I worked and Suffolk where I lived. I made the change to Engine Ice just a few years ago because I felt the need to get it closer to the target 180 at speed on really hot days. Maybe it helped a bit, maybe not. I still see 190 at speed on days where it's probably too hot to ride. I don't think it was any change in the bike's behavior that made me want to do it, maybe it was reading Shazaam's post!

The 916, I can't say. It's a parts bike built up from pretty much every year and model of the series with a fair share of aftermarket stuff tossed in... Aside from the rims and side fairings, no two parts are from the same bike. The bike has behaved as I describe since its beginning. Given the two bikes exhibit the same thermal characteristics, I figure I am at least in a safe operating condition. All the cooling system stuff, except the Engine Ice, is factory spec. No mods.

Let us know how it works out, maybe you're on to something. Everyone focuses on moving more air across the radiator, I don't recall anyone working on coolant flow. There was a guy in the Superbike forum that stuffed a huge radiator in his 998. He said made a big improvement, not very elegant looking, but it worked for him. I have settled on the probability that it's not an issue, but I certainly get where people are coming from here. These things get hot, seems really bad but I can't recall anyone having heat relayed failures, or at lease chronic ones from a bike operating normally.

Dan. "Painfully mistaking my big talk for the truth" Samantha Fish.
2003 ST4s (The Truck)
1995 916 (Junk Yard Dog)
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