9 blade impeller versus 12 blade impeller

[PJCruising]

I have a Yanmar 4JH2-HTE engine which takes an impeller that is 9 bladed. It's Yanmar p.n. 129470-42532. Just got a price for a spare from my local Yanmar distributor at $78.60! Good grief, almost $80 for an impeller.
Searching online, I see that there are several manufacturers selling 12 bladed impellers that are compatible with this Yanmar part number for half the cost.
Looking for feedback from our community on how well these alternative impellers work.
thanks

[Lee Jerry]

No experience with those 12-blade impellers, but an observation.

If the two impellers are made out of the same material, then it seems to me that one of two things (or some of both) must be true:

-If the blades are made the same thickness (size and strength), the there is more 'rubber' in there and less water, and thus less water will be pumped with each revolution.

- If the blades are made thinner (so that the entrained water is the same and thus pump capacity), then they will be weaker and won't last as long. (I suppose it could be possible, but seems unlikely, that they are made stronger and also cheaper.)

[RaymondR]

Originally Posted by Lee Jerry

- If the blades are made thinner (so that the entrained water is the same and thus pump capacity), then they will be weaker and won't last as long. (I suppose it could be possible, but seems unlikely, that they are made stronger and also cheaper.)

Maybe not.

More blades will share less load per blade and the bending stress in the blade is considerably decreased by making them thinner.

For that sort of savings I'd give them a try, there's no catastrophic failure mode.

[bil56]

not 80$
https://www.ebay.com/itm/111608376840

[pcmm]

Originally Posted by PJCruising

I have a Yanmar 4JH2-HTE engine which takes an impeller that is 9 bladed. It's Yanmar p.n. 129470-42532. Just got a price for a spare from my local Yanmar distributor at $78.60! Good grief, almost $80 for an impeller.
Searching online, I see that there are several manufacturers selling 12 bladed impellers that are compatible with this Yanmar part number for half the cost.
Looking for feedback from our community on how well these alternative impellers work.
thanks

$80 thats a deal! where I am, the same impeller is $120. I've used the 12 blade knockoff impeller before and it just doesn't seem to pump as well as the 9 bladed. For better or worse I stick with the 9 blade that Yanmar specs for the pump.

[roryboy]

It was a while back. I installed a Beta impeller in the yanmar pump and it cooled fine. Cost less then $30. I think it had 12 blades.

[Tsuru]

I have an industry. Background in pump operation and have rebuilt about a dozen raw water pumps for past boats and for friends. Parts were sourced from OEM, bearing and seal distributors and the Ebay seller in the post above (Marine Parts and Pumps).
https://www.ebay.com/itm/111608376840

The parts from Marine Parts and Pumps were OEM quality and Steve from Marine Parts Pumps is knowledgeable and honest.

I’d recommend contacting Steve and ask the same question. If the answer sounds reasonable give it a shot. Then just to be safe do an inspection after about 10 hours of operation.

My gut feeling is that it will be fine, but do have concerns that other posters have temperature problems. No matter what you decide use impeller lubricant during installation.

[skipperpete]

Originally Posted by PJCruising

I have a Yanmar 4JH2-HTE engine which takes an impeller that is 9 bladed. It's Yanmar p.n. 129470-42532. Just got a price for a spare from my local Yanmar distributor at $78.60! Good grief, almost $80 for an impeller.
Searching online, I see that there are several manufacturers selling 12 bladed impellers that are compatible with this Yanmar part number for half the cost.
Looking for feedback from our community on how well these alternative impellers work.
thanks

Stick with the Yanmar impeller but only if it has the thread into the bronze spline to accommodate the Yanmar impeller removal tool. It’s a bugger of a job when the impeller gets stuck and you have to remove the pump to use the conventional jabsco impeller puller……. Unless you happen to be lucky enough to have the forward facing pump.

[Lee Jerry]

Originally Posted by RaymondR

Maybe not.

More blades will share less load per blade and the bending stress in the blade is considerably decreased by making them thinner.

I don't think the "load per blade" has much (if anything) to do with the process of actually pumping the water. I think it is simply due to the geometry of the pump that forces the blades to bend. It's essentially the same whether fluid is being pumped or not (ignoring potential heat and friction). In other words, I don't think "load per blade" has any real effect on durability of the impeller.

For that sort of savings I'd give them a try, there's no catastrophic failure mode.

I strongly disagree with this. There are (at least) two potential catastrophic failure modes possible. First is loss of cooling water and overheating of the engine. This is of course bad, and there are measures taken to prevent this before the major damage occurs (such as temp gauges and alarms, and seeing / hearing the cooling water coming out of the engine). Second is the impeller coming apart and little bits of rubber clogging the downstream cooling passages. This can (will!) lead to the first problem, but is a pain to fix, and the only prevention is to replace the impeller before it happens (i.e. at regular intervals).

[RaymondR]

I've had two Yanmars in my life and whilst they are great motors Yanmars parts pricing policies are a national scandal.

Years ago I had a 3GM30 which needed a replacement raw water pump. I was quoted $850 for the Yanmar pump which was basically a Johnston pump with a flange mounting onto a steel bracket. The same Johnston pump with a pedestal mount was $300. I purchased the pedestal pump and fabricated a bracket from a small piece of aluminium angle iron. It's about fifteen years later now and I still feel good about the $500 saving every time I remember the incident.

I had a similar experience with the alternator on the same engine which had a Nickendenso alternator on it which I was quoted around $1,000 to replace. I altered the mount and replaced the original with a larger capacity Bosch Universal for about $160.

Now, if I was replacing the mains or big end bearings I would probably use genuine Yanmar parts but for those bolt on items where the risk is slight and the savings significant I accept the risk. Particularly if the item is one which is replaced regularly at relatively short intervals.

[skipperpete]

Interesting about the relative stiffness of the blades, I just recently replaced a Yanmar 12 blade impeller after a huge battle, it was stuck on the spline…..this was a non genuine 12 blade impeller and in round 1 of the extraction, 2 of the blades tore off ( ya can’t lever em out on a 4JH because of the fragile oring groove) in the vycegrip jaws. Half a day later with the pump on the dock I put in a new 12 blade impeller with the internal thread so next time it will only take 10 mins to change…….. but here’s the point, the 12 blade impeller is very flexible and easy to install by hand with a slurp of dishwashing liquid but the 9 blade ones are much stiffer and always put up a fight, often needing a zip tie to get em started in to the housing…. I suspect that the stiffer impellers are capable of higher pressures while the 12 blade ones bend as the restriction to flow increases but I’ve noticed that 9 blade impellers fail more frequently than the softer 12’s.

[PJCruising]

Thanks to everyone for their feedback on these impellers. Note the Ebay link is for the 12 blade impeller; my $80 comment was the pricing given by my local Yanmar dealer for the 9 blade impeller. My R/W pump faces aft and is in a tough spot to access, right under the alternator. What was the design engineer thinking! My old Perkins R/W pump was a belt drive mounted right in front; could change an impeller or the whole pump itself in a jiffy. Not so with this Yanmar.
I'll have to pick up the impeller removal tool mentioned, I can see where that would be a great assist in getting the old one out. Not a heck of a lot of room to access the pump location.
I do also have a wet exhaust temp alarm on the this motor that I added. Just a temperature "button" one clamps to the wet exhaust hose right after the injection elbow. If the impeller fails or water intake gets plugged, this alarm kicks off before the engine temp alarms. An inexpensive alarm to add and saved my bacon once years ago in the South Pacific.

[pcmm]

I think the aft facing impeller access on the 4JH series was brilliant thinking on Yanmars part! For my application anyway. My center cockpit has great access from the side doors to the engine room. The impeller is right there, if it had been on the front of the engine, it would have been a pain to deal with! I like the idea of the "Yanmar tool" but since the superseded part number no longer has the threads, its of little use to me. I just use a pair of hose pliers to grab the hub and lever it out.

[NBs]

As far as I remember, in my northen light generator, the original impellee had abundant wings and it often broke down. I replaced it with a cheap 6 wing one used on a volvo 2003 machine and they now last for years / +600 hours vs half a year and about 150-200 hours

[David Mathis]

As to capacity, is 9/9 more than 12/12? I've used the cheaper aftermarket impellers on my Yanmar generator for many years without issue. The impeller gets changed about every 4-5 years with no failures or heating issues. The generator runs a lot since we have 120V refrigerator, freezer, ice maker, dual air conditioners, etc. We live on the boat much of the summer and anchor often. As to difficulty in removing the impeller, the first time changing was challenging until a sharp chisel was used to remove the vanes then it came off without difficulty. Now, Neverseize (an incredibly messy graphite/grease product) is applied to the shaft before installing the new one which greatly eases the removal.