Cooling System Refresh - Stewart WP?

So the time has finally come to overhaul my cooling system. I just had a question, I was looking into getting the Stewart WP because of the various claimed advantages (SS impeller, good bearings, increased flow). I don't really have a problem with the price but my question is this: the rest of the cooling system will be restored with OEM parts (including behr Rad unless someone can convince me otherwise). Will the Stewart water pump and its increased "flow" make the other parts inclined to fail faster? Or will I be ok with all stock minus the Stewart?

Originally Posted by ianbsmith

So the time has finally come to overhaul my cooling system. I just had a question, I was looking into getting the Stewart WP because of the various claimed advantages (SS impeller, good bearings, increased flow). I don't really have a problem with the price but my question is this: the rest of the cooling system will be restored with OEM parts (including behr Rad unless someone can convince me otherwise). Will the Stewart water pump and its increased "flow" make the other parts inclined to fail faster? Or will I be ok with all stock minus the Stewart?

IMHO science says you are adding additional stress to the belt for additional flow. That being said I would think that the stress is virtually insignificant in relation to total stress exerted on the belt.

If had to wager my guess is the added stress will make a part fail in 9.6 years vs 10 years. This could be offset from the ever so slightly cooler engine.

In other words, no studies have been done on this but I do not hear of any major issues associated with the Stewart Pump.

==> As for me, I'd simply switch to the same OEM pump flow with metal impellers vs the standard plastic impellers. My car was optimized to run at a preset temperature and I want to keep it there. The engineers factored in metal expansion based on heat when they made these cars which is one reason they run smoother AFTER they warm up. Colder does not equate to better. Optimum operating temperature is the target to shoot for.

Well I'm actually having all the belts and tensioners done at the same time so ill be ok there.

And it shouldn't make it run cooler since the thermostat controls that, it should just allow the system to cool more effectively if it desires (???)

I think anyway...

The Stewart water pump has limited advantages. While flowrate is higher, it serves no tangible benefit, since the operating temp is controlled by the thermostat. I would think that the Stewart is built of higher quality components (bearings, shaft, etc.) to greater precision. This should translate to increased durability. Whether that is worth 4X the cost of an alternative WP (Behr, Hepu, etc.) is a subjective matter. I figure an alternative WP is good for about 100K. 2 replacements is the max I figure I will ever need. Hence, I just saved $120 for a different repair. FWIW, I used Hepu.

Kind of like a Bulova versus a Rolex: they both tell time. If the Bulova is quartz, it'll tell more accurate time.

I typed /waterpump in the bestlinks and found this, among others:
- What brand of waterpump to buy (1)

From another forum, same question, and I quote myself:
"I was skeptical at first with the high performace Stewart WP, but I bit the bullet and purchased it. I also purchased the TMS underdrive pulleys. I was thinking lower rpm's & higher flow = stock flow, but longer bearing life on the WP.
The outcome is very positive: I believe I still get a tad more flow than the stock setup. I experience very RARELY temps of 96°C in heavy stop-and-go traffic, and they last only a glimpse - seconds at most. With the stock WP, i experienced 98°C steady in heavy traffic, with the max posted temp staying solid. When the original clutch fan bit the dust, the temps started to creep higher.
For warm weather states, the Stewart WP is a Godsend. Literally."

Originally Posted by ianbsmith

Well I'm actually having all the belts and tensioners done at the same time so ill be ok there.

And it shouldn't make it run cooler since the thermostat controls that, it should just allow the system to cool more effectively if it desires (???)

I think anyway...

You are correct about the thermostat opening at a preset temp. However increased heat transfer rate also impacts operating temp. Earlier this year someone posted before and after pics of the engine temp gauge.

The needle was pointing strait up before the Stewart WP. The needle was almost two needles width left of the center mark after the install.

We must consider the heat sensor is in a fixed location of the engine. Thus the heat was being transferred away from that location at a greater rate.

If you are in a hot climate where even when the thermostat opens the heat exceeds optimum temps the added flow may be the route to go.

So your saying that a pump like the Hepu is probably the way to go? It does get pretty warm here, but it also gets pretty nippy in the winter.

Also my wallet is feeling a little thin today since a construction site curb decided to attack my wheel at speed yesterday.........

I have had the HEPU now for 6 years, zero problems.

Save your money for beers!

People often spend serious money for good looking wheels or other cosmetic enhancements for these cars. Spending $100 more for a heavy duty water pump with a lifetime warranty doesn't seem unreasonable. I've gone through several water pumps in the 12 years I've had my 528. The peace of mind of not having to worry about it any more is worth it to me. The extra output is a bonus.

Well, I really appreciate the input everyone! I ended up getting the HEPU WP because it seemed like it was the best combination of benefit to cost. Although the Stewart may have been a little bit better, I feel like that money could be better spent on some other maintainance or improvement (because the list never really ends does it?)

Ill keep you guys posted as to my impressions once I get the work done (also having all the belt related stuff done at the same time).

Originally Posted by daw

Spending $100 more for a heavy duty water pump with a lifetime warranty doesn't seem unreasonable.

Personally, I wouldn't spend a penny for a so-called 'lifetime warranty'.

Details here:
- Deciding whether or not a replacement-part lifetime warranty make sense (1)

And, I'd use whatever water pump cn90 uses!

But here's a summary early on from the referenced thread ...

BMW E39 Water Pump Suppliers:
--- top tier (I think) ---
1. Stewart EMP (some say they beef up the bearings to handle the metal)
2. Hepu (Cam like's em but I don't know much about 'em)
3. Geba (heavy cast metal impeller, bearings sometimes fail)
4. Graf welded steel impeller (better but also occasional bearing failure)
5. GMB (I think this is OE with composite plastic impellers???)
--- lower tier (I think) ---
6. Hella (I think this is OEM with composite plastic impellers)
7. Bosch (I don't know of any users who reported back on these)
8. Beck Arnley (they sell 'em but I don't know anyone using them)
9. Airtex (again, they sell 'em, but we'd have to hear from users first)
10. AC Delco (same as the last two above, they sell 'em)
11. A1 Cardone (they sell 'em, don't know much about 'em)
12. ??? please correct this list as needed so we all benefit ???